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Varieties
Heavy body acrylics are typically found in the Artist and Student Grade paints. "Heavy Body" refers to the viscosity or thickness of the paint. They are the best choice for impasto or heavier paint applications and will hold a brush or knife stroke and even a medium stiff peak. Gel Mediums ("pigment-less paints") are also available in various viscosities and used to thicken or thin paints, as well as extend paints and add transparency.
Examples of Heavy Body Acrylics are Matisse Structure Acrylic Colors, Lukas Pastos Acrylics, Liquitex Heavy Body Acrylics and Golden Heavy Body Acrylics.
Medium viscosity acrylics – Fluid acrylics, Soft body acrylics, or High Flow acrylics – have a lower viscosity but generally the same pigmentation as the Heavy Body acrylics. Available in either Artist quality or Craft quality, the cost and quality vary accordingly. These paints are good for watercolor techniques, airbrush application, or when smooth coverage is desired. Fluid acrylics can be mixed with any medium to thicken them for impasto work, or to thin them for glazing applications.
Examples of fluid acrylics include Lukascryl Liquid, Lukascryl Studio, Liquitex Soft Body and Golden Fluid acrylics.
Open acrylics were created to address the one major difference between oil and acrylic paints: the shortened time it takes acrylic paints to dry. Designed by Golden Artist Colors, Inc. with a hydrophilic acrylic resin, these paints can take anywhere from a few hours to a few days, or even weeks, to dry completely, depending on paint thickness, support characteristics, temperature, and humidity.
Iridescent, pearl and interference acrylic colors combine conventional pigments with powdered mica (aluminium silicate) or powdered bronze to achieve complex visual effects. Colors have shimmering or reflective characteristics, depending on the coarseness or fineness of the powder. Iridescent colors are used in fine arts and crafts. | Acrylic paint | Wikipedia | 432 | 2838 | https://en.wikipedia.org/wiki/Acrylic%20paint | Technology | Artist's and drafting tools | null |
Acrylic gouache is like traditional gouache because it dries to a matte, opaque finish. However, unlike traditional gouache, the acrylic binder makes it water-resistant once it dries. Like craft paint, it will adhere to a variety of surfaces, not only canvas and paper. This paint is typically used by water-colorists, cartoonists, or illustrators, and for decorative or folk art applications.
Examples of acrylic gouache are Lascaux Gouache and Turner Acryl Gouache.
Craft acrylics can be used on surfaces besides canvas, such as wood, metal, fabrics, and ceramics. They are used in decorative painting techniques and faux finishes to decorate objects of ordinary life. Although colors can be mixed, pigments are often not specified. Each color line is formulated instead to achieve a wide range of premixed colors. Craft paints usually employ vinyl or PVA resins to increase adhesion and lower cost.
Interactive acrylics are all-purpose acrylic artists' colors which have the characteristic fast-drying nature of artists' acrylics, but are formulated to allow artists to delay drying when they need more working time, or re-wet their work when they want to do more wet blending.
Exterior acrylics are paints that can withstand outdoor conditions. Like craft acrylics, they adhere to many surfaces. They are more resistant to both water and ultraviolet light. This makes them the acrylic of choice for architectural murals, outdoor signs, and many faux-finishing techniques.
Acrylic glass paint is water-based and semi-permanent, making it a suitable paint for temporary displays on glass windows.
Acrylic enamel paint creates a smooth, hard shell. It can be oven-baked or air dried. It can be permanent if kept away from harsh conditions such as dishwashing. | Acrylic paint | Wikipedia | 386 | 2838 | https://en.wikipedia.org/wiki/Acrylic%20paint | Technology | Artist's and drafting tools | null |
Differences between acrylic and oil paint
The vehicle and binder of oil paints is linseed oil (or another drying oil), whereas acrylic paint has water as the vehicle for an emulsion (suspension) of acrylic polymer, which serves as the binder. Thus, oil paint is said to be "oil-based", whereas acrylic paint is "water-based" (or sometimes "water-borne").
The main practical difference between most acrylics and oil paints is the inherent drying time. Oils allow for more time to blend colors and apply even glazes over underpaintings. This slow-drying aspect of oil can be seen as an advantage for certain techniques, but it impedes an artist trying to work quickly. The fast evaporation of water from regular acrylic paint films can be slowed with the use of acrylic retarders. Retarders are generally glycol or glycerin-based additives. The addition of a retarder slows the evaporation rate of the water.
Oil paints may require the use of solvents such as mineral spirits or turpentine to thin the paint and clean up. These solvents generally have some level of toxicity and can be found objectionable. Relatively recently, water-miscible oil paints have been developed for artists' use. Oil paint films can gradually yellow and lose their flexibility over time creating cracks in the paint film; the "fat over lean" rule must be observed to ensure its durability.
Oil paint has a higher pigment load than acrylic paint. As linseed oil contains a smaller molecule than acrylic paint, oil paint is able to absorb substantially more pigment. Oil provides a refractive index that is less clear than acrylic dispersions, which imparts a unique "look and feel" to the resultant paint film. Not all the pigments of oil paints are available in acrylics and vice versa, as each medium has different chemical sensitivities. Some historical pigments are alkali sensitive, and therefore cannot be made in an acrylic emulsion; others are just too difficult to formulate. Approximate "hue" color formulations, that do not contain the historical pigments, are typically offered as substitutes. | Acrylic paint | Wikipedia | 474 | 2838 | https://en.wikipedia.org/wiki/Acrylic%20paint | Technology | Artist's and drafting tools | null |
Because of acrylic paint's more flexible nature and more consistent drying time between layers, an artist does not have to follow the same rules of oil painting, where more medium must be applied to each layer to avoid cracking. It usually takes 10–20 minutes for one to two layers of acrylic paint to dry, depending on the brand, quality, and humidity levels of the surrounding environment. Some professional grades of acrylic paint can take 20–30 minutes or even more than an hour. Although canvas needs to be properly primed before painting with oils to prevent the paint medium from eventually rotting the canvas, acrylic can be safely applied straight to the canvas. The rapid drying of acrylic paint tends to discourage blending of color and use of wet-in-wet technique as in oil painting. Even though acrylic retarders can slow drying time to several hours, it remains a relatively fast-drying medium and adding too much acrylic retarder can prevent the paint from ever drying properly.
Meanwhile, acrylic paint is very elastic, which prevents cracking from occurring. Acrylic paint's binder is acrylic polymer emulsion – as this binder dries, the paint remains flexible.
Another difference between oil and acrylic paints is the versatility offered by acrylic paints. Acrylics are very useful in mixed media, allowing the use of pastel (oil and chalk), charcoal and pen (among others) on top of the dried acrylic painted surface. Mixing other bodies into the acrylic is possible—sand, rice, and even pasta may be incorporated in the artwork. Mixing artist or student grade acrylic paint with household acrylic emulsions is possible, allowing the use of premixed tints straight from the tube or tin, and thereby presenting the painter with a vast color range at their disposal. This versatility is also illustrated by the variety of additional artistic uses for acrylics. Specialized acrylics have been manufactured and used for linoblock printing (acrylic block printing ink has been produced by Derivan since the early 1980s), face painting, airbrushing, watercolor-like techniques, and fabric screen printing. | Acrylic paint | Wikipedia | 457 | 2838 | https://en.wikipedia.org/wiki/Acrylic%20paint | Technology | Artist's and drafting tools | null |
Another difference between oil and acrylic paint is the cleanup. Acrylic paint can be cleaned out of a brush with any soap, while oil paint needs a specific type to be sure to get all the oil out of the brushes. Also, it is easier to let a palette with oil paint dry and then scrape the paint off, whereas one can easily clean wet acrylic paint with water.
Difference between acrylic and watercolor paint
The biggest difference is that acrylic paint is opaque, whereas watercolor paint is translucent in nature. Watercolors take about 5 to 15 minutes to dry while acrylics take about 10 to 20 minutes. In order to change the tone or shade of a watercolor pigment, one changes the percentage of water mixed in to the color. For brighter colors, one adds more water. For darker colors, one adds less water. In order to create lighter or darker colors with acrylic paints, one adds white or black.
Another difference is that watercolors must be painted onto a porous surface, primarily watercolor paper. Acrylic paints can be used on many different surfaces.
Both acrylic and watercolor are easy to clean up with water. Acrylic paint should be cleaned with soap and water immediately following use. Watercolor paint can be cleaned with just water. | Acrylic paint | Wikipedia | 270 | 2838 | https://en.wikipedia.org/wiki/Acrylic%20paint | Technology | Artist's and drafting tools | null |
Angular momentum (sometimes called moment of momentum or rotational momentum) is the rotational analog of linear momentum. It is an important physical quantity because it is a conserved quantity – the total angular momentum of a closed system remains constant. Angular momentum has both a direction and a magnitude, and both are conserved. Bicycles and motorcycles, flying discs, rifled bullets, and gyroscopes owe their useful properties to conservation of angular momentum. Conservation of angular momentum is also why hurricanes form spirals and neutron stars have high rotational rates. In general, conservation limits the possible motion of a system, but it does not uniquely determine it.
The three-dimensional angular momentum for a point particle is classically represented as a pseudovector , the cross product of the particle's position vector (relative to some origin) and its momentum vector; the latter is in Newtonian mechanics. Unlike linear momentum, angular momentum depends on where this origin is chosen, since the particle's position is measured from it.
Angular momentum is an extensive quantity; that is, the total angular momentum of any composite system is the sum of the angular momenta of its constituent parts. For a continuous rigid body or a fluid, the total angular momentum is the volume integral of angular momentum density (angular momentum per unit volume in the limit as volume shrinks to zero) over the entire body.
Similar to conservation of linear momentum, where it is conserved if there is no external force, angular momentum is conserved if there is no external torque. Torque can be defined as the rate of change of angular momentum, analogous to force. The net external torque on any system is always equal to the total torque on the system; the sum of all internal torques of any system is always 0 (this is the rotational analogue of Newton's third law of motion). Therefore, for a closed system (where there is no net external torque), the total torque on the system must be 0, which means that the total angular momentum of the system is constant.
The change in angular momentum for a particular interaction is called angular impulse, sometimes twirl. Angular impulse is the angular analog of (linear) impulse.
Examples
The trivial case of the angular momentum of a body in an orbit is given by
where is the mass of the orbiting object, is the orbit's frequency and is the orbit's radius.
The angular momentum of a uniform rigid sphere rotating around its axis, instead, is given by | Angular momentum | Wikipedia | 493 | 2839 | https://en.wikipedia.org/wiki/Angular%20momentum | Physical sciences | Classical mechanics | null |
where is the sphere's mass, is the frequency of rotation and is the sphere's radius.
Thus, for example, the orbital angular momentum of the Earth with respect to the Sun is about 2.66 × 1040 kg⋅m2⋅s−1, while its rotational angular momentum is about 7.05 × 1033 kg⋅m2⋅s−1.
In the case of a uniform rigid sphere rotating around its axis, if, instead of its mass, its density is known, the angular momentum is given by
where is the sphere's density, is the frequency of rotation and is the sphere's radius.
In the simplest case of a spinning disk, the angular momentum is given by
where is the disk's mass, is the frequency of rotation and is the disk's radius.
If instead the disk rotates about its diameter (e.g. coin toss), its angular momentum is given by
Definition in classical mechanics
Just as for angular velocity, there are two special types of angular momentum of an object: the spin angular momentum is the angular momentum about the object's centre of mass, while the orbital angular momentum is the angular momentum about a chosen center of rotation. The Earth has an orbital angular momentum by nature of revolving around the Sun, and a spin angular momentum by nature of its daily rotation around the polar axis. The total angular momentum is the sum of the spin and orbital angular momenta. In the case of the Earth the primary conserved quantity is the total angular momentum of the solar system because angular momentum is exchanged to a small but important extent among the planets and the Sun. The orbital angular momentum vector of a point particle is always parallel and directly proportional to its orbital angular velocity vector ω, where the constant of proportionality depends on both the mass of the particle and its distance from origin. The spin angular momentum vector of a rigid body is proportional but not always parallel to the spin angular velocity vector Ω, making the constant of proportionality a second-rank tensor rather than a scalar.
Orbital angular momentum in two dimensions | Angular momentum | Wikipedia | 415 | 2839 | https://en.wikipedia.org/wiki/Angular%20momentum | Physical sciences | Classical mechanics | null |
Angular momentum is a vector quantity (more precisely, a pseudovector) that represents the product of a body's rotational inertia and rotational velocity (in radians/sec) about a particular axis. However, if the particle's trajectory lies in a single plane, it is sufficient to discard the vector nature of angular momentum, and treat it as a scalar (more precisely, a pseudoscalar). Angular momentum can be considered a rotational analog of linear momentum. Thus, where linear momentum is proportional to mass and linear speed
angular momentum is proportional to moment of inertia and angular speed measured in radians per second.
Unlike mass, which depends only on amount of matter, moment of inertia depends also on the position of the axis of rotation and the distribution of the matter. Unlike linear velocity, which does not depend upon the choice of origin, orbital angular velocity is always measured with respect to a fixed origin. Therefore, strictly speaking, should be referred to as the angular momentum relative to that center.
In the case of circular motion of a single particle, we can use and to expand angular momentum as reducing to:
the product of the radius of rotation and the linear momentum of the particle , where is the linear (tangential) speed.
This simple analysis can also apply to non-circular motion if one uses the component of the motion perpendicular to the radius vector:
where is the perpendicular component of the motion. Expanding, rearranging, and reducing, angular momentum can also be expressed,
where is the length of the moment arm, a line dropped perpendicularly from the origin onto the path of the particle. It is this definition, , to which the term moment of momentum refers.
Scalar angular momentum from Lagrangian mechanics
Another approach is to define angular momentum as the conjugate momentum (also called canonical momentum) of the angular coordinate expressed in the Lagrangian of the mechanical system. Consider a mechanical system with a mass constrained to move in a circle of radius in the absence of any external force field. The kinetic energy of the system is
And the potential energy is
Then the Lagrangian is
The generalized momentum "canonically conjugate to" the coordinate is defined by
Orbital angular momentum in three dimensions | Angular momentum | Wikipedia | 458 | 2839 | https://en.wikipedia.org/wiki/Angular%20momentum | Physical sciences | Classical mechanics | null |
To completely define orbital angular momentum in three dimensions, it is required to know the rate at which the position vector sweeps out angle, the direction perpendicular to the instantaneous plane of angular displacement, and the mass involved, as well as how this mass is distributed in space. By retaining this vector nature of angular momentum, the general nature of the equations is also retained, and can describe any sort of three-dimensional motion about the center of rotation – circular, linear, or otherwise. In vector notation, the orbital angular momentum of a point particle in motion about the origin can be expressed as:
where
is the moment of inertia for a point mass,
is the orbital angular velocity of the particle about the origin,
is the position vector of the particle relative to the origin, and ,
is the linear velocity of the particle relative to the origin, and
is the mass of the particle.
This can be expanded, reduced, and by the rules of vector algebra, rearranged:
which is the cross product of the position vector and the linear momentum of the particle. By the definition of the cross product, the vector is perpendicular to both and . It is directed perpendicular to the plane of angular displacement, as indicated by the right-hand rule – so that the angular velocity is seen as counter-clockwise from the head of the vector. Conversely, the vector defines the plane in which and lie.
By defining a unit vector perpendicular to the plane of angular displacement, a scalar angular speed results, where
and
where is the perpendicular component of the motion, as above.
The two-dimensional scalar equations of the previous section can thus be given direction:
and for circular motion, where all of the motion is perpendicular to the radius .
In the spherical coordinate system the angular momentum vector expresses as
Analogy to linear momentum
Angular momentum can be described as the rotational analog of linear momentum. Like linear momentum it involves elements of mass and displacement. Unlike linear momentum it also involves elements of position and shape.
Many problems in physics involve matter in motion about some certain point in space, be it in actual rotation about it, or simply moving past it, where it is desired to know what effect the moving matter has on the point—can it exert energy upon it or perform work about it? Energy, the ability to do work, can be stored in matter by setting it in motion—a combination of its inertia and its displacement. Inertia is measured by its mass, and displacement by its velocity. Their product, | Angular momentum | Wikipedia | 503 | 2839 | https://en.wikipedia.org/wiki/Angular%20momentum | Physical sciences | Classical mechanics | null |
is the matter's momentum. Referring this momentum to a central point introduces a complication: the momentum is not applied to the point directly. For instance, a particle of matter at the outer edge of a wheel is, in effect, at the end of a lever of the same length as the wheel's radius, its momentum turning the lever about the center point. This imaginary lever is known as the moment arm. It has the effect of multiplying the momentum's effort in proportion to its length, an effect known as a moment. Hence, the particle's momentum referred to a particular point,
is the angular momentum, sometimes called, as here, the moment of momentum of the particle versus that particular center point. The equation combines a moment (a mass turning moment arm ) with a linear (straight-line equivalent) speed . Linear speed referred to the central point is simply the product of the distance and the angular speed versus the point: another moment. Hence, angular momentum contains a double moment: Simplifying slightly, the quantity is the particle's moment of inertia, sometimes called the second moment of mass. It is a measure of rotational inertia.
The above analogy of the translational momentum and rotational momentum can be expressed in vector form:
for linear motion
for rotation
The direction of momentum is related to the direction of the velocity for linear movement. The direction of angular momentum is related to the angular velocity of the rotation.
Because moment of inertia is a crucial part of the spin angular momentum, the latter necessarily includes all of the complications of the former, which is calculated by multiplying elementary bits of the mass by the squares of their distances from the center of rotation. Therefore, the total moment of inertia, and
the angular momentum, is a complex function of the configuration of the matter about the center of rotation and the orientation of the rotation for the various bits.
For a rigid body, for instance a wheel or an asteroid, the orientation of rotation is simply the position of the rotation axis versus the matter of the body. It may or may not pass through the center of mass, or it may lie completely outside of the body. For the same body, angular momentum may take a different value for every possible axis about which rotation may take place. It reaches a minimum when the axis passes through the center of mass. | Angular momentum | Wikipedia | 479 | 2839 | https://en.wikipedia.org/wiki/Angular%20momentum | Physical sciences | Classical mechanics | null |
For a collection of objects revolving about a center, for instance all of the bodies of the Solar System, the orientations may be somewhat organized, as is the Solar System, with most of the bodies' axes lying close to the system's axis. Their orientations may also be completely random.
In brief, the more mass and the farther it is from the center of rotation (the longer the moment arm), the greater the moment of inertia, and therefore the greater the angular momentum for a given angular velocity. In many cases the moment of inertia, and hence the angular momentum, can be simplified by,
where is the radius of gyration, the distance from the axis at which the entire mass may be considered as concentrated.
Similarly, for a point mass the moment of inertia is defined as,
where is the radius of the point mass from the center of rotation, and for any collection of particles as the sum,
Angular momentum's dependence on position and shape is reflected in its units versus linear momentum: kg⋅m2/s or N⋅m⋅s for angular momentum versus kg⋅m/s or N⋅s for linear momentum. When calculating angular momentum as the product of the moment of inertia times the angular velocity, the angular velocity must be expressed in radians per second, where the radian assumes the dimensionless value of unity. (When performing dimensional analysis, it may be productive to use orientational analysis which treats radians as a base unit, but this is not done in the International system of units). The units if angular momentum can be interpreted as torque⋅time. An object with angular momentum of can be reduced to zero angular velocity by an angular impulse of .
The plane perpendicular to the axis of angular momentum and passing through the center of mass is sometimes called the invariable plane, because the direction of the axis remains fixed if only the interactions of the bodies within the system, free from outside influences, are considered. One such plane is the invariable plane of the Solar System.
Angular momentum and torque
Newton's second law of motion can be expressed mathematically,
or force = mass × acceleration. The rotational equivalent for point particles may be derived as follows:
which means that the torque (i.e. the time derivative of the angular momentum) is
Because the moment of inertia is , it follows that , and which, reduces to | Angular momentum | Wikipedia | 492 | 2839 | https://en.wikipedia.org/wiki/Angular%20momentum | Physical sciences | Classical mechanics | null |
This is the rotational analog of Newton's second law. Note that the torque is not necessarily proportional or parallel to the angular acceleration (as one might expect). The reason for this is that the moment of inertia of a particle can change with time, something that cannot occur for ordinary mass.
Conservation of angular momentum
General considerations
A rotational analog of Newton's third law of motion might be written, "In a closed system, no torque can be exerted on any matter without the exertion on some other matter of an equal and opposite torque about the same axis." Hence, angular momentum can be exchanged between objects in a closed system, but total angular momentum before and after an exchange remains constant (is conserved).
Seen another way, a rotational analogue of Newton's first law of motion might be written, "A rigid body continues in a state of uniform rotation unless acted upon by an external influence." Thus with no external influence to act upon it, the original angular momentum of the system remains constant.
The conservation of angular momentum is used in analyzing central force motion. If the net force on some body is directed always toward some point, the center, then there is no torque on the body with respect to the center, as all of the force is directed along the radius vector, and none is perpendicular to the radius. Mathematically, torque because in this case and are parallel vectors. Therefore, the angular momentum of the body about the center is constant. This is the case with gravitational attraction in the orbits of planets and satellites, where the gravitational force is always directed toward the primary body and orbiting bodies conserve angular momentum by exchanging distance and velocity as they move about the primary. Central force motion is also used in the analysis of the Bohr model of the atom.
For a planet, angular momentum is distributed between the spin of the planet and its revolution in its orbit, and these are often exchanged by various mechanisms. The conservation of angular momentum in the Earth–Moon system results in the transfer of angular momentum from Earth to Moon, due to tidal torque the Moon exerts on the Earth. This in turn results in the slowing down of the rotation rate of Earth, at about 65.7 nanoseconds per day, and in gradual increase of the radius of Moon's orbit, at about 3.82 centimeters per year. | Angular momentum | Wikipedia | 475 | 2839 | https://en.wikipedia.org/wiki/Angular%20momentum | Physical sciences | Classical mechanics | null |
The conservation of angular momentum explains the angular acceleration of an ice skater as they bring their arms and legs close to the vertical axis of rotation. By bringing part of the mass of their body closer to the axis, they decrease their body's moment of inertia. Because angular momentum is the product of moment of inertia and angular velocity, if the angular momentum remains constant (is conserved), then the angular velocity (rotational speed) of the skater must increase.
The same phenomenon results in extremely fast spin of compact stars (like white dwarfs, neutron stars and black holes) when they are formed out of much larger and slower rotating stars.
Conservation is not always a full explanation for the dynamics of a system but is a key constraint. For example, a spinning top is subject to gravitational torque making it lean over and change the angular momentum about the nutation axis, but neglecting friction at the point of spinning contact, it has a conserved angular momentum about its spinning axis, and another about its precession axis. Also, in any planetary system, the planets, star(s), comets, and asteroids can all move in numerous complicated ways, but only so that the angular momentum of the system is conserved.
Noether's theorem states that every conservation law is associated with a symmetry (invariant) of the underlying physics. The symmetry associated with conservation of angular momentum is rotational invariance. The fact that the physics of a system is unchanged if it is rotated by any angle about an axis implies that angular momentum is conserved.
Relation to Newton's second law of motion
While angular momentum total conservation can be understood separately from Newton's laws of motion as stemming from Noether's theorem in systems symmetric under rotations, it can also be understood simply as an efficient method of calculation of results that can also be otherwise arrived at directly from Newton's second law, together with laws governing the forces of nature (such as Newton's third law, Maxwell's equations and Lorentz force). Indeed, given initial conditions of position and velocity for every point, and the forces at such a condition, one may use Newton's second law to calculate the second derivative of position, and solving for this gives full information on the development of the physical system with time. Note, however, that this is no longer true in quantum mechanics, due to the existence of particle spin, which is angular momentum that cannot be described by the cumulative effect of point-like motions in space. | Angular momentum | Wikipedia | 504 | 2839 | https://en.wikipedia.org/wiki/Angular%20momentum | Physical sciences | Classical mechanics | null |
As an example, consider decreasing of the moment of inertia, e.g. when a figure skater is pulling in their hands, speeding up the circular motion. In terms of angular momentum conservation, we have, for angular momentum L, moment of inertia I and angular velocity ω:
Using this, we see that the change requires an energy of:
so that a decrease in the moment of inertia requires investing energy.
This can be compared to the work done as calculated using Newton's laws. Each point in the rotating body is accelerating, at each point of time, with radial acceleration of:
Let us observe a point of mass m, whose position vector relative to the center of motion is perpendicular to the z-axis at a given point of time, and is at a distance z. The centripetal force on this point, keeping the circular motion, is:
Thus the work required for moving this point to a distance dz farther from the center of motion is:
For a non-pointlike body one must integrate over this, with m replaced by the mass density per unit z. This gives:
which is exactly the energy required for keeping the angular momentum conserved.
Note, that the above calculation can also be performed per mass, using kinematics only. Thus the phenomena of figure skater accelerating tangential velocity while pulling their hands in, can be understood as follows in layman's language: The skater's palms are not moving in a straight line, so they are constantly accelerating inwards, but do not gain additional speed because the accelerating is always done when their motion inwards is zero. However, this is different when pulling the palms closer to the body: The acceleration due to rotation now increases the speed; but because of the rotation, the increase in speed does not translate to a significant speed inwards, but to an increase of the rotation speed.
Stationary-action principle
In classical mechanics it can be shown that the rotational invariance of action functionals implies conservation of angular momentum. The action is defined in classical physics as a functional of positions, often represented by the use of square brackets, and the final and initial times. It assumes the following form in cartesian coordinates:where the repeated indices indicate summation over the index. If the action is invariant of an infinitesimal transformation, it can be mathematically stated as: .
Under the transformation, , the action becomes:
where we can employ the expansion of the terms up-to first order in :
giving the following change in action: | Angular momentum | Wikipedia | 512 | 2839 | https://en.wikipedia.org/wiki/Angular%20momentum | Physical sciences | Classical mechanics | null |
Since all rotations can be expressed as matrix exponential of skew-symmetric matrices, i.e. as where is a skew-symmetric matrix and is angle of rotation, we can express the change of coordinates due to the rotation , up-to first order of infinitesimal angle of rotation, as:
Combining the equation of motion and rotational invariance of action, we get from the above equations that:Since this is true for any matrix that satisfies it results in the conservation of the following quantity:
as . This corresponds to the conservation of angular momentum throughout the motion.
Lagrangian formalism
In Lagrangian mechanics, angular momentum for rotation around a given axis, is the conjugate momentum of the generalized coordinate of the angle around the same axis. For example, , the angular momentum around the z axis, is:
where is the Lagrangian and is the angle around the z axis.
Note that , the time derivative of the angle, is the angular velocity . Ordinarily, the Lagrangian depends on the angular velocity through the kinetic energy: The latter can be written by separating the velocity to its radial and tangential part, with the tangential part at the x-y plane, around the z-axis, being equal to:
where the subscript i stands for the i-th body, and m, vT and ωz stand for mass, tangential velocity around the z-axis and angular velocity around that axis, respectively.
For a body that is not point-like, with density ρ, we have instead:
where integration runs over the area of the body, and Iz is the moment of inertia around the z-axis.
Thus, assuming the potential energy does not depend on ωz (this assumption may fail for electromagnetic systems), we have the angular momentum of the ith object:
We have thus far rotated each object by a separate angle; we may also define an overall angle θz by which we rotate the whole system, thus rotating also each object around the z-axis, and have the overall angular momentum:
From Euler–Lagrange equations it then follows that:
Since the lagrangian is dependent upon the angles of the object only through the potential, we have:
which is the torque on the ith object. | Angular momentum | Wikipedia | 472 | 2839 | https://en.wikipedia.org/wiki/Angular%20momentum | Physical sciences | Classical mechanics | null |
Suppose the system is invariant to rotations, so that the potential is independent of an overall rotation by the angle θz (thus it may depend on the angles of objects only through their differences, in the form ). We therefore get for the total angular momentum:
And thus the angular momentum around the z-axis is conserved.
This analysis can be repeated separately for each axis, giving conversation of the angular momentum vector. However, the angles around the three axes cannot be treated simultaneously as generalized coordinates, since they are not independent; in particular, two angles per point suffice to determine its position. While it is true that in the case of a rigid body, fully describing it requires, in addition to three translational degrees of freedom, also specification of three rotational degrees of freedom; however these cannot be defined as rotations around the Cartesian axes (see Euler angles). This caveat is reflected in quantum mechanics in the non-trivial commutation relations of the different components of the angular momentum operator.
Hamiltonian formalism
Equivalently, in Hamiltonian mechanics the Hamiltonian can be described as a function of the angular momentum. As before, the part of the kinetic energy related to rotation around the z-axis for the ith object is:
which is analogous to the energy dependence upon momentum along the z-axis, .
Hamilton's equations relate the angle around the z-axis to its conjugate momentum, the angular momentum around the same axis:
The first equation gives
And so we get the same results as in the Lagrangian formalism.
Note, that for combining all axes together, we write the kinetic energy as:
where pr is the momentum in the radial direction, and the moment of inertia is a 3-dimensional matrix; bold letters stand for 3-dimensional vectors.
For point-like bodies we have:
This form of the kinetic energy part of the Hamiltonian is useful in analyzing central potential problems, and is easily transformed to a quantum mechanical work frame (e.g. in the hydrogen atom problem).
Angular momentum in orbital mechanics
While in classical mechanics the language of angular momentum can be replaced by Newton's laws of motion, it is particularly useful for motion in central potential such as planetary motion in the solar system. Thus, the orbit of a planet in the solar system is defined by its energy, angular momentum and angles of the orbit major axis relative to a coordinate frame.
In astrodynamics and celestial mechanics, a quantity closely related to angular momentum is defined as | Angular momentum | Wikipedia | 510 | 2839 | https://en.wikipedia.org/wiki/Angular%20momentum | Physical sciences | Classical mechanics | null |
called specific angular momentum. Note that Mass is often unimportant in orbital mechanics calculations, because motion of a body is determined by gravity. The primary body of the system is often so much larger than any bodies in motion about it that the gravitational effect of the smaller bodies on it can be neglected; it maintains, in effect, constant velocity. The motion of all bodies is affected by its gravity in the same way, regardless of mass, and therefore all move approximately the same way under the same conditions.
Solid bodies
Angular momentum is also an extremely useful concept for describing rotating rigid bodies such as a gyroscope or a rocky planet.
For a continuous mass distribution with density function ρ(r), a differential volume element dV with position vector r within the mass has a mass element dm = ρ(r)dV. Therefore, the infinitesimal angular momentum of this element is:
and integrating this differential over the volume of the entire mass gives its total angular momentum:
In the derivation which follows, integrals similar to this can replace the sums for the case of continuous mass.
Collection of particles
For a collection of particles in motion about an arbitrary origin, it is informative to develop the equation of angular momentum by resolving their motion into components about their own center of mass and about the origin. Given,
is the mass of particle ,
is the position vector of particle w.r.t. the origin,
is the velocity of particle w.r.t. the origin,
is the position vector of the center of mass w.r.t. the origin,
is the velocity of the center of mass w.r.t. the origin,
is the position vector of particle w.r.t. the center of mass,
is the velocity of particle w.r.t. the center of mass,
The total mass of the particles is simply their sum,
The position vector of the center of mass is defined by,
By inspection,
and
The total angular momentum of the collection of particles is the sum of the angular momentum of each particle,
Expanding ,
Expanding ,
It can be shown that (see sidebar),
and
therefore the second and third terms vanish,
The first term can be rearranged,
and total angular momentum for the collection of particles is finally, | Angular momentum | Wikipedia | 461 | 2839 | https://en.wikipedia.org/wiki/Angular%20momentum | Physical sciences | Classical mechanics | null |
The first term is the angular momentum of the center of mass relative to the origin. Similar to , below, it is the angular momentum of one particle of mass M at the center of mass moving with velocity V. The second term is the angular momentum of the particles moving relative to the center of mass, similar to , below. The result is general—the motion of the particles is not restricted to rotation or revolution about the origin or center of mass. The particles need not be individual masses, but can be elements of a continuous distribution, such as a solid body.
Rearranging equation () by vector identities, multiplying both terms by "one", and grouping appropriately,
gives the total angular momentum of the system of particles in terms of moment of inertia and angular velocity ,
Single particle case
In the case of a single particle moving about the arbitrary origin,
and equations () and () for total angular momentum reduce to,
Case of a fixed center of mass
For the case of the center of mass fixed in space with respect to the origin,
and equations () and () for total angular momentum reduce to,
Angular momentum in general relativity
In modern (20th century) theoretical physics, angular momentum (not including any intrinsic angular momentum – see below) is described using a different formalism, instead of a classical pseudovector. In this formalism, angular momentum is the 2-form Noether charge associated with rotational invariance. As a result, angular momentum is generally not conserved locally for general curved spacetimes, unless they have rotational symmetry; whereas globally the notion of angular momentum itself only makes sense if the spacetime is asymptotically flat. If the spacetime is only axially symmetric like for the Kerr metric, the total angular momentum is not conserved but is conserved which is related to the invariance of rotating around the symmetry-axis, where note that where is the metric, is the rest mass, is the four-velocity, and is the four-position in spherical coordinates.
In classical mechanics, the angular momentum of a particle can be reinterpreted as a plane element:
in which the exterior product (∧) replaces the cross product (×) (these products have similar characteristics but are nonequivalent). This has the advantage of a clearer geometric interpretation as a plane element, defined using the vectors x and p, and the expression is true in any number of dimensions. In Cartesian coordinates:
or more compactly in index notation: | Angular momentum | Wikipedia | 506 | 2839 | https://en.wikipedia.org/wiki/Angular%20momentum | Physical sciences | Classical mechanics | null |
The angular velocity can also be defined as an anti-symmetric second order tensor, with components ωij. The relation between the two anti-symmetric tensors is given by the moment of inertia which must now be a fourth order tensor:
Again, this equation in L and ω as tensors is true in any number of dimensions. This equation also appears in the geometric algebra formalism, in which L and ω are bivectors, and the moment of inertia is a mapping between them.
In relativistic mechanics, the relativistic angular momentum of a particle is expressed as an anti-symmetric tensor of second order:
in terms of four-vectors, namely the four-position X and the four-momentum P, and absorbs the above L together with the moment of mass, i.e., the product of the relativistic mass of the particle and its centre of mass, which can be thought of as describing the motion of its centre of mass, since mass–energy is conserved.
In each of the above cases, for a system of particles the total angular momentum is just the sum of the individual particle angular momenta, and the centre of mass is for the system.
Angular momentum in quantum mechanics
In quantum mechanics, angular momentum (like other quantities) is expressed as an operator, and its one-dimensional projections have quantized eigenvalues. Angular momentum is subject to the Heisenberg uncertainty principle, implying that at any time, only one projection (also called "component") can be measured with definite precision; the other two then remain uncertain. Because of this, the axis of rotation of a quantum particle is undefined. Quantum particles do possess a type of non-orbital angular momentum called "spin", but this angular momentum does not correspond to a spinning motion. In relativistic quantum mechanics the above relativistic definition becomes a tensorial operator.
Spin, orbital, and total angular momentum
The classical definition of angular momentum as can be carried over to quantum mechanics, by reinterpreting r as the quantum position operator and p as the quantum momentum operator. L is then an operator, specifically called the orbital angular momentum operator. The components of the angular momentum operator satisfy the commutation relations of the Lie algebra so(3). Indeed, these operators are precisely the infinitesimal action of the rotation group on the quantum Hilbert space. ( | Angular momentum | Wikipedia | 490 | 2839 | https://en.wikipedia.org/wiki/Angular%20momentum | Physical sciences | Classical mechanics | null |
The plum pudding model was the first scientific model of the atom to describe an internal structure. It was first proposed by J. J. Thomson in 1904 following his discovery of the electron in 1897, and was rendered obsolete by Ernest Rutherford's discovery of the atomic nucleus in 1911. The model tried to account for two properties of atoms then known: that there are electrons, and that atoms have no net electric charge. Logically there had to be an equal amount of positive charge to balance out the negative charge of the electrons. As Thomson had no idea as to the source of this positive charge, he tentatively proposed that it was everywhere in the atom, and that the atom was spherical. This was the mathematically simplest hypothesis to fit the available evidence, or lack thereof. In such a sphere, the negatively charged electrons would distribute themselves in a more or less even manner throughout the volume, simultaneously repelling each other while being attracted to the positive sphere's center.
Despite Thomson's efforts, his model couldn't account for emission spectra and valencies. Based on experimental studies of alpha particle scattering (in the gold foil experiment), Ernest Rutherford developed an alternative model for the atom featuring a compact nucleus where the positive charge is concentrated.
Thomson's model is popularly referred to as the "plum pudding model" with the notion that the electrons are distributed uniformly like raisins in a plum pudding. Neither Thomson nor his colleagues ever used this analogy. It seems to have been coined by popular science writers to make the model easier to understand for the layman. The analogy is perhaps misleading because Thomson likened the positive sphere to a liquid rather than a solid since he thought the electrons moved around in it.
Significance
Thomson's model marks the moment when the development of atomic theory passed from chemists to physicists. While atomic theory was widely accepted by chemists by the end of the 19th century, physicists remained skeptical because the atomic model lacked any properties which concerned their field, such as electric charge, magnetic moment, volume, or absolute mass. Thomson himself was a physicist and his atomic model was a byproduct of his investigations of cathode rays, by which he discovered electrons. Thomson hypothesized that the quantity, arrangement, and motions of electrons in the atom could explain its physical and chemical properties, such as emission spectra, valencies, reactivity, and ionization. He was on the right track, though his approach was based on classical mechanics and he did not have the insight to incorporate quantized energy into it. | Plum pudding model | Wikipedia | 512 | 2840 | https://en.wikipedia.org/wiki/Plum%20pudding%20model | Physical sciences | Atomic physics | Physics |
Background
Throughout the 19th century evidence from chemistry and statistical mechanics accumulated that matter was composed of atoms. The structure of the atom was discussed, and by the end of the century the leading model was the vortex theory of the atom, proposed by William Thomson (later Lord Kelvin) in 1867. By 1890, J.J. Thomson had his own version called the "nebular atom" hypothesis, in which atoms were composed of immaterial vortices and suggested similarities between the arrangement of vortices and periodic regularity found among the chemical elements.
Thomson's discovery of the electron in 1897 changed his views. Thomson called them "corpuscles" (particles), but they were more commonly called "electrons", the name G. J. Stoney had coined for the "fundamental unit quantity of electricity" in 1891. However even late in 1899, few scientists believed in subatomic particles.
Another emerging scientific theme of the 19th century was the discovery and study of radioactivity. Thomson discovered the electron by studying cathode rays, and in 1900 Henri Becquerel determined that the radiation from uranium, now called beta particles, had the same charge/mass ratio as cathode rays. These beta particles were believed to be electrons travelling at high speed. The particles were used by Thomson to probe atoms to find evidence for his atomic theory. The other form of radiation critical to this era of atomic models was alpha particles. Heavier and slower than beta particles, these were the key tool used by Rutherford to find evidence against Thomson's model.
In addition to the emerging atomic theory, the electron, and radiation, the last element of history was the many studies of atomic spectra published in the late 19th century. Part of the attraction of the vortex model was its possible role in describing the spectral data as vibrational responses to electromagnetic radiation. Neither Thomson's model nor its successor, Rutherford's model, made progress towards understanding atomic spectra. That would have to wait until Niels Bohr built the first quantum-based atom model. | Plum pudding model | Wikipedia | 411 | 2840 | https://en.wikipedia.org/wiki/Plum%20pudding%20model | Physical sciences | Atomic physics | Physics |
Development
Thomson's model was the first to assign a specific inner structure to an atom, though his earliest descriptions did not include mathematical formulas.
From 1897 through 1913, Thomson proposed a series of increasingly detailed polyelectron models for the atom. His first versions were qualitative culminating in his 1906 paper and follow on summaries. Thomson's model changed over the course of its initial publication, finally becoming a model with much more mobility containing electrons revolving in the dense field of positive charge rather than a static structure. Thomson attempted unsuccessfully to reshape his model to account for some of the major spectral lines experimentally known for several elements.
1897 Corpuscles inside atoms
In a paper titled Cathode Rays, Thomson demonstrated that cathode rays are not light but made of negatively charged particles which he called corpuscles. He observed that cathode rays can be deflected by electric and magnetic fields, which does not happen with light rays. In a few paragraphs near the end of this long paper Thomson discusses the possibility that atoms were made of these corpuscles, calling them primordial atoms. Thomson believed that the intense electric field around the cathode caused the surrounding gas molecules to split up into their component corpuscles, thereby generating cathode rays. Thomson thus showed evidence that atoms were divisible, though he did not attempt to describe their structure at this point.
Thomson notes that he was not the first scientist to propose that atoms are divisible, making reference to William Prout who in 1815 found that the atomic weights of various elements were multiples of hydrogen's atomic weight and hypothesised that all atoms were made of hydrogen atoms fused together. Prout's hypothesis was dismissed by chemists when by the 1830s it was found that some elements seemed to have a non-integer atomic weight—e.g. chlorine has an atomic weight of about 35.45. But the idea continued to intrigue scientists. The discrepancies were eventually explained with the discovery of isotopes in 1912.
A few months after Thomson's paper appeared, George FitzGerald suggested that the corpuscle identified by Thomson from cathode rays and proposed as parts of an atom was a "free electron", as described by physicist Joseph Larmor and Hendrik Lorentz. While Thomson did not adopt the terminology, the connection convinced other scientists that cathode rays were particles, an important step in their eventual acceptance of an atomic model based on sub-atomic particles. | Plum pudding model | Wikipedia | 504 | 2840 | https://en.wikipedia.org/wiki/Plum%20pudding%20model | Physical sciences | Atomic physics | Physics |
In 1899 Thomson reiterated his atomic model in a paper that showed that negative electricity created by ultraviolet light landing on a metal (known now as the photoelectric effect) has the same mass-to-charge ratio as cathode rays; then he applied his previous method for determining the charge on ions to the negative electric particles created by ultraviolet light. He estimated that the electron's mass was 0.0014 times that of the hydrogen ion (as a fraction: ). In the conclusion of this paper he writes:
1904 Mechanical model of the atom
Thomson provided his first detailed description of the atom in his 1904 paper On the Structure of the Atom.
Thomson starts with a short description of his model
... the atoms of the elements consist of a number of negatively electrified corpuscles enclosed in a sphere of uniform positive electrification, ...
Primarily focused on the electrons, Thomson adopted the positive sphere from Kelvin's atom model proposed a year earlier.
He then gives a detailed mechanical analysis of such a system, distributing the electrons uniformly around a ring. The attraction of the positive electrification is balanced by the mutual repulsion of the electrons. His analysis focuses on stability, looking for cases where small changes in position are countered by restoring forces.
After discussing his many formulae for stability he turned to analysing patterns in the number of electrons in various concentric rings of stable configurations. These regular patterns Thomson argued are analogous to the periodic law of chemistry behind the structure of the periodic table. This concept, that a model based on subatomic particles could account for chemical trends, encouraged interest in Thomson's model and influenced future work even if the details Thomson's electron assignments turned out to be incorrect.
Thomson at this point believed that all the mass of the atom was carried by the electrons. This would mean that even a small atom would have to contain thousands of electrons, and the positive electrification that encapsulated them was without mass.
1905 lecture on electron arrangements
In a lecture delivered to the Royal Institution of Great Britain in 1905, Thomson explained that it was too computationally difficult for him to calculate the movements of large numbers of electrons in the positive sphere, so he proposed a practical experiment. This involved magnetised pins pushed into cork discs and set afloat in a basin of water. The pins were oriented such that they repelled each other. Above the centre of the basin was suspended an electromagnet that attracted the pins. The equilibrium arrangement the pins took informed Thomson on what arrangements the electrons in an atom might take. | Plum pudding model | Wikipedia | 509 | 2840 | https://en.wikipedia.org/wiki/Plum%20pudding%20model | Physical sciences | Atomic physics | Physics |
For instance, he observed that while five pins would arrange themselves in a stable pentagon around the centre, six pins could not form a stable hexagon. Instead, one pin would move to the centre and the other five would form a pentagon around the centre pin, and this arrangement was stable. As he added more pins, they would arrange themselves in concentric rings around the centre.
The experiment functioned in two dimensions instead of three, but Thomson inferred the electrons in the atom arranged themselves in concentric shells and the could move within these shells but did not move from one shell to another them except when electrons were added or subtracted from the atom.
1906 Estimating electrons per atom
Before 1906 Thomson considered the atomic weight to be due to the mass of the electrons (which he continued to call "corpuscles"). Based on his own estimates of the electron mass, an atom would need tens of thousands electrons to account for the mass. In 1906 he used three different methods, X-ray scattering, beta ray absorption, or optical properties of gases, to estimate that "number of corpuscles is not greatly different from the atomic weight". This reduced the number of electrons to tens or at most a couple of hundred and that in turn meant that the positive sphere in Thomson's model contained most of the mass of the atom. This meant that Thomson's mechanical stability work from 1904 and the comparison to the periodic table were no longer valid. Moreover, the alpha particle, so important to the next advance in atomic theory by Rutherford, would no longer be viewed as an atom containing thousands of electrons.
In 1907, Thomson published The Corpuscular Theory of Matter which reviewed his ideas on the atom's structure and proposed further avenues of research.
In Chapter 6, he further elaborates his experiment using magnetised pins in water, providing an expanded table. For instance, if 59 pins were placed in the pool, they would arrange themselves in concentric rings of the order 20-16-13-8-2 (from outermost to innermost). | Plum pudding model | Wikipedia | 414 | 2840 | https://en.wikipedia.org/wiki/Plum%20pudding%20model | Physical sciences | Atomic physics | Physics |
In Chapter 7, Thomson summarised his 1906 results on the number of electrons in an atom. He included one important correction: he replaced the beta-particle analysis with one based on the cathode ray experiments of August Becker, giving a result in better agreement with other approaches to the problem. Experiments by other scientists in this field had shown that atoms contain far fewer electrons than Thomson previously thought. Thomson now believed the number of electrons in an atom was a small multiple of its atomic weight: "the number of corpuscles in an atom of any element is proportional to the atomic weight of the element — it is a multiple, and not a large one, of the atomic weight of the element." This meant that almost all of the atom's mass had to be carried by the positive sphere, whatever it was made of.
Thomson in this book estimated that a hydrogen atom is 1,700 times heavier than an electron (the current measurement is 1,837). Thomson noted that no scientist had yet found a positively charged particle smaller than a hydrogen ion. He also wrote that the positive charge of an atom is a multiple of a basic unit of positive charge, equal to the negative charge of an electron. Thomson refused to jump to the conclusion that the basic unit of positive charge has a mass equal to that of the hydrogen ion, arguing that scientists first had to know how many electrons an atom contains. For all he could tell, a hydrogen ion might still contain a few electrons—perhaps two electrons and three units of positive charge.
1910 Multiple scattering
Thomson's difficulty with beta scattering in 1906 lead him to renewed interest in the topic. He encouraged J. Arnold Crowther to experiment with beta scattering through thin foils and, in 1910, Thomson produced a new theory of beta scattering. The two innovations in this paper was the introduction of scattering from the positive sphere of the atom and analysis that multiple or compound scattering was critical to the final results. This theory and Crowther's experimental results would be confronted by Rutherford's theory and Geiger and Mardsen new experiments with alpha particles. | Plum pudding model | Wikipedia | 422 | 2840 | https://en.wikipedia.org/wiki/Plum%20pudding%20model | Physical sciences | Atomic physics | Physics |
Another innovation in Thomson's 1910 paper was that he modelled how an atom might deflect an incoming beta particle if the positive charge of the atom existed in discrete units of equal but arbitrary size, spread evenly throughout the atom, separated by empty space, with each unit having a positive charge equal to the electron's negative charge. Thomson therefore came close to deducing the existence of the proton, which was something Rutherford eventually did. In Rutherford's model of the atom, the protons are clustered in a very small nucleus, but in Thomson's alternative model, the positive units were spread throughout the atom.
Thomson's 1910 scattering model
In his 1910 paper "On the Scattering of rapidly moving Electrified Particles", Thomson presented equations that modelled how beta particles scatter in a collision with an atom. His work was based on beta scattering studies by James Crowther.
Deflection by the positive sphere
Thomson typically assumed the positive charge in the atom was uniformly distributed throughout its volume, encapsulating the electrons. In his 1910 paper, Thomson presented the following equation which isolated the effect of this positive sphere:
where k is the Coulomb constant, qe is the charge of the beta particle, qg is the charge of the positive sphere, m is the mass of the beta particle, and R is the radius of the sphere. Because the atom is many thousands of times heavier than the beta particle, no correction for recoil is needed.
Thomson did not explain how this equation was developed, but the historian John L. Heilbron provided an educated guess he called a "straight-line" approximation. Consider a beta particle passing through the positive sphere with its initial trajectory at a lateral distance b from the centre. The path is assumed to have a very small deflection and therefore is treated here as a straight line.
Inside a sphere of uniformly distributed positive charge the force exerted on the beta particle at any point along its path through the sphere would be directed along the radius with magnitude:
The component of force perpendicular to the trajectory and thus deflecting the path of the particle would be:
The lateral change in momentum py is therefore
The resulting angular deflection, , is given by
where px is the average horizontal momentum taken to be equal to the incoming momentum. Since we already know the deflection is very small, we can treat as being equal to . | Plum pudding model | Wikipedia | 482 | 2840 | https://en.wikipedia.org/wiki/Plum%20pudding%20model | Physical sciences | Atomic physics | Physics |
To find the average deflection angle , the angle for each value of b and the corresponding L are added across the face sphere, then divided by the cross-section area. per Pythagorean theorem.
This matches Thomson's formula in his 1910 paper.
Deflection by the electrons
Thomson modelled the collisions between a beta particle and the electrons of an atom by calculating the deflection of one collision then multiplying by a factor for the number of collisions as the particle crosses the atom.
For the electrons within an arbitrary distance s of the beta particle's path, their mean distance will be . Therefore, the average deflection per electron will be
where qe is the elementary charge, k is the Coulomb constant, m and v are the mass and velocity of the beta particle.
The factor for the number of collisions was known to be the square root of the number of possible electrons along path. The number of electrons depends upon the density of electrons along the particle path times the path length L.
The net deflection caused by all the electrons within this arbitrary cylinder of effect around the beta particle's path is
where N0 is the number of electrons per unit volume and is the volume of this cylinder.
Since Thomson calculated the deflection would be very small, he treats L as a straight line. Therefore where b is the distance of this chord from the centre. The mean of is given by the integral
We can now replace in the equation for to obtain the mean deflection :
where N is the number of electrons in the atom, equal to .
Deflection by the positive charge in discrete units
In his 1910 paper, Thomson proposed an alternative model in which the positive charge exists in discrete units separated by empty space, with those units being evenly distributed throughout the atom's volume.
In this concept, the average scattering angle of the beta particle is given by:
where σ is the ratio of the volume occupied by the positive charge to the volume of the whole atom. Thomson did not explain how he arrived at this equation.
Net deflection
To find the combined effect of the positive charge and the electrons on the beta particle's path, Thomson provided the following equation:
Demise of the plum pudding model | Plum pudding model | Wikipedia | 453 | 2840 | https://en.wikipedia.org/wiki/Plum%20pudding%20model | Physical sciences | Atomic physics | Physics |
Thomson probed the structure of atoms through beta particle scattering, whereas his former student Ernest Rutherford was interested in alpha particle scattering. Beta particles are electrons emitted by radioactive decay, whereas alpha particles are essentially helium atoms, also emitted in process of decay. Alpha particles have considerably more momentum than beta particles and Rutherford found that matter scatters alpha particles in ways that Thomson's plum pudding model could not predict.
Between 1908 and 1913, Ernest Rutherford, Hans Geiger, and Ernest Marsden collaborated on a series of experiments in which they bombarded thin metal foils with a beam of alpha particles and measured the intensity versus scattering angle of the particles. They found that the metal foil could scatter alpha particles by more than 90°. This should not have been possible according to the Thomson model: the scattering into large angles should have been negligible. The odds of a beta particle being scattered by more than 90° under such circumstances is astronomically small, and since alpha particles typically have much more momentum than beta particles, their deflection should be smaller still. The Thomson models simply could not produce electrostatic forces of sufficient strength to cause such large deflection. The charges in the Thomson model were too diffuse. This led Rutherford to discard the Thomson for a new model where the positive charge of the atom is concentrated in a tiny nucleus.
Rutherford went on to make more compelling discoveries. In Thomson's model, the positive charge sphere was just an abstract component, but Rutherford found something concrete to attribute the positive charge to: particles he dubbed "protons". Whereas Thomson believed that the electron count was roughly correlated to the atomic weight, Rutherford showed that (in a neutral atom) it is exactly equal to the atomic number.
Thomson hypothesised that the arrangement of the electrons in the atom somehow determined the spectral lines of a chemical element. He was on the right track, but it had nothing to do with how atoms circulated in a sphere of positive charge. Scientists eventually discovered that it had to do with how electrons absorb and release energy in discrete quantities, moving through energy levels which correspond to emission and absorption spectra. Thomson had not incorporated quantum mechanics into his atomic model, which at the time was a very new field of physics. Niels Bohr and Erwin Schroedinger later incorporated quantum mechanics into the atomic model.
Rutherford's nuclear model | Plum pudding model | Wikipedia | 471 | 2840 | https://en.wikipedia.org/wiki/Plum%20pudding%20model | Physical sciences | Atomic physics | Physics |
Rutherford's 1911 paper on alpha particle scattering showed that Thomson's scattering model could not explain the large angle scattering and it showed that multiple scattering was not necessary to explain the data. However, in the years immediately following its publication few scientists took note. The scattering model predictions were not considered definitive evidence against Thomson's plum pudding model. Thomson and Rutherford had pioneered scattering as a technique to probe atoms, its reliability and value were unproven. Before Rutherford's paper the alpha particle was considered an atom, not a compact mass. It was not clear why it should be a good probe. Moreover, Rutherford's paper did not discuss the atomic electrons vital to practical problems like chemistry or atomic spectroscopy. Rutherford's nuclear model would only become widely accepted after the work of Niels Bohr.
Mathematical Thomson problem
The Thomson problem in mathematics seeks the optimal distribution of equal point charges on the surface of a sphere. Unlike the original Thomson atomic model, the sphere in this purely mathematical model does not have a charge, and this causes all the point charges to move to the surface of the sphere by their mutual repulsion. There is still no general solution to Thomson's original problem of how electrons arrange themselves within a sphere of positive charge.
Origin of the nickname
The first known writer to compare Thomson's model to a plum pudding was an anonymous reporter in an article for the British pharmaceutical magazine The Chemist and Druggist in August 1906.
The analogy was never used by Thomson nor his colleagues. It seems to have been a conceit of popular science writers to make the model easier to understand for the layman. | Plum pudding model | Wikipedia | 324 | 2840 | https://en.wikipedia.org/wiki/Plum%20pudding%20model | Physical sciences | Atomic physics | Physics |
Atomic theory is the scientific theory that matter is composed of particles called atoms. The definition of the word "atom" has changed over the years in response to scientific discoveries. Initially, it referred to a hypothetical concept of there being some fundamental particle of matter, too small to be seen by the naked eye, that could not be divided. Then the definition was refined to being the basic particles of the chemical elements, when chemists observed that elements seemed to combine with each other in ratios of small whole numbers. Then physicists discovered that these particles had an internal structure of their own and therefore perhaps did not deserve to be called "atoms", but renaming atoms would have been impractical by that point.
Atomic theory is one of the most important scientific developments in history, crucial to all the physical sciences. At the start of The Feynman Lectures on Physics, physicist and Nobel laureate Richard Feynman offers the atomic hypothesis as the single most prolific scientific concept.
Philosophical atomism
The basic idea that matter is made up of tiny indivisible particles is an old idea that appeared in many ancient cultures. The word atom is derived from the ancient Greek word atomos, which means "uncuttable". This ancient idea was based in philosophical reasoning rather than scientific reasoning. Modern atomic theory is not based on these old concepts. In the early 19th century, the scientist John Dalton noticed that chemical substances seemed to combine with each other by discrete and consistent units of weight, and he decided to use the word atom to refer to these units. | History of atomic theory | Wikipedia | 309 | 2844 | https://en.wikipedia.org/wiki/History%20of%20atomic%20theory | Physical sciences | Atomic physics | null |
Groundwork
Working in the late 17th century, Robert Boyle developed the concept of a chemical element as substance different from a compound.
Near the end of the 18th century, a number of important developments in chemistry emerged without referring to the notion of an atomic theory. The first was Antoine Lavoisier who showed that compounds consist of elements in constant proportion, redefining an element as a substance which scientists could not decompose into simpler substances by experimentation. This brought an end to the ancient idea of the elements of matter being fire, earth, air, and water, which had no experimental support. Lavoisier showed that water can be decomposed into hydrogen and oxygen, which in turn he could not decompose into anything simpler, thereby proving these are elements. Lavoisier also defined the law of conservation of mass, which states that in a chemical reaction, matter does not appear nor disappear into thin air; the total mass remains the same even if the substances involved were transformed. Finally, there was the law of definite proportions, established by the French chemist Joseph Proust in 1797, which states that if a compound is broken down into its constituent chemical elements, then the masses of those constituents will always have the same proportions by weight, regardless of the quantity or source of the original compound. This definition distinguished compounds from mixtures.
Dalton's law of multiple proportions
John Dalton studied data gathered by himself and by other scientists. He noticed a pattern that later came to be known as the law of multiple proportions: in compounds which contain two particular elements, the amount of Element A per measure of Element B will differ across these compounds by ratios of small whole numbers. This suggested that each element combines with other elements in multiples of a basic quantity. | History of atomic theory | Wikipedia | 354 | 2844 | https://en.wikipedia.org/wiki/History%20of%20atomic%20theory | Physical sciences | Atomic physics | null |
In 1804, Dalton explained his atomic theory to his friend and fellow chemist Thomas Thomson, who published an explanation of Dalton's theory in his book A System of Chemistry in 1807. According to Thomson, Dalton's idea first occurred to him when experimenting with "olefiant gas" (ethylene) and "carburetted hydrogen gas" (methane). Dalton found that "carburetted hydrogen gas" contains twice as much hydrogen per measure of carbon as "olefiant gas", and concluded that a molecule of "olefiant gas" is one carbon atom and one hydrogen atom, and a molecule of "carburetted hydrogen gas" is one carbon atom and two hydrogen atoms. In reality, an ethylene molecule has two carbon atoms and four hydrogen atoms (C2H4), and a methane molecule has one carbon atom and four hydrogen atoms (CH4). In this particular case, Dalton was mistaken about the formulas of these compounds, and it wasn't his only mistake. But in other cases, he got their formulas right, as in the following examples:
Example 1 — tin oxides: Dalton identified two types of tin oxide. One is a grey powder that Dalton referred to as "the protoxide of tin", which is 88.1% tin and 11.9% oxygen. The other is a white powder which Dalton referred to as "the deutoxide of tin", which is 78.7% tin and 21.3% oxygen. Adjusting these figures, in the grey powder there is about 13.5 g of oxygen for every 100 g of tin, and in the white powder there is about 27 g of oxygen for every 100 g of tin. 13.5 and 27 form a ratio of 1:2. These compounds are known today as tin(II) oxide (SnO) and tin(IV) oxide (SnO2). In Dalton's terminology, a "protoxide" is a molecule containing a single oxygen atom, and a "deutoxide" molecule has two. The modern equivalents of his terms would be monoxide and dioxide. | History of atomic theory | Wikipedia | 434 | 2844 | https://en.wikipedia.org/wiki/History%20of%20atomic%20theory | Physical sciences | Atomic physics | null |
Example 2 — iron oxides: Dalton identified two oxides of iron. There is one type of iron oxide that is a black powder which Dalton referred to as "the protoxide of iron", which is 78.1% iron and 21.9% oxygen. The other iron oxide is a red powder, which Dalton referred to as "the intermediate or red oxide of iron" which is 70.4% iron and 29.6% oxygen. Adjusting these figures, in the black powder there is about 28 g of oxygen for every 100 g of iron, and in the red powder there is about 42 g of oxygen for every 100 g of iron. 28 and 42 form a ratio of 2:3. These compounds are iron(II) oxide and iron(III) oxide and their formulas are Fe2O2 and Fe2O3 respectively (iron(II) oxide's formula is normally written as FeO, but here it is written as Fe2O2 to contrast it with the other oxide). Dalton described the "intermediate oxide" as being "2 atoms protoxide and 1 of oxygen", which adds up to two atoms of iron and three of oxygen. That averages to one and a half atoms of oxygen for every iron atom, putting it midway between a "protoxide" and a "deutoxide".
Example 3 — nitrogen oxides: Dalton was aware of three oxides of nitrogen: "nitrous oxide", "nitrous gas", and "nitric acid". These compounds are known today as nitrous oxide, nitric oxide, and nitrogen dioxide respectively. "Nitrous oxide" is 63.3% nitrogen and 36.7% oxygen, which means it has 80 g of oxygen for every 140 g of nitrogen. "Nitrous gas" is 44.05% nitrogen and 55.95% oxygen, which means there is 160 g of oxygen for every 140 g of nitrogen. "Nitric acid" is 29.5% nitrogen and 70.5% oxygen, which means it has 320 g of oxygen for every 140 g of nitrogen. 80 g, 160 g, and 320 g form a ratio of 1:2:4. The formulas for these compounds are N2O, NO, and NO2. | History of atomic theory | Wikipedia | 465 | 2844 | https://en.wikipedia.org/wiki/History%20of%20atomic%20theory | Physical sciences | Atomic physics | null |
Dalton defined an atom as being the "ultimate particle" of a chemical substance, and he used the term "compound atom" to refer to "ultimate particles" which contain two or more elements. This is inconsistent with the modern definition, wherein an atom is the basic particle of a chemical element and a molecule is an agglomeration of atoms. The term "compound atom" was confusing to some of Dalton's contemporaries as the word "atom" implies indivisibility, but he responded that if a carbon dioxide "atom" is divided, it ceases to be carbon dioxide. The carbon dioxide "atom" is indivisible in the sense that it cannot be divided into smaller carbon dioxide particles.
Dalton made the following assumptions on how "elementary atoms" combined to form "compound atoms" (what we today refer to as molecules). When two elements can only form one compound, he assumed it was one atom of each, which he called a "binary compound". If two elements can form two compounds, the first compound is a binary compound and the second is a "ternary compound" consisting of one atom of the first element and two of the second. If two elements can form three compounds between them, then the third compound is a "quaternary" compound containing one atom of the first element and three of the second. Dalton thought that water was a "binary compound", i.e. one hydrogen atom and one oxygen atom. Dalton did not know that in their natural gaseous state, the ultimate particles of oxygen, nitrogen, and hydrogen exist in pairs (O2, N2, and H2). Nor was he aware of valencies. These properties of atoms were discovered later in the 19th century. | History of atomic theory | Wikipedia | 353 | 2844 | https://en.wikipedia.org/wiki/History%20of%20atomic%20theory | Physical sciences | Atomic physics | null |
Because atoms were too small to be directly weighed using the methods of the 19th century, Dalton instead expressed the weights of the myriad atoms as multiples of the hydrogen atom's weight, which Dalton knew was the lightest element. By his measurements, 7 grams of oxygen will combine with 1 gram of hydrogen to make 8 grams of water with nothing left over, and assuming a water molecule to be one oxygen atom and one hydrogen atom, he concluded that oxygen's atomic weight is 7. In reality it is 16. Aside from the crudity of early 19th century measurement tools, the main reason for this error was that Dalton didn't know that the water molecule in fact has two hydrogen atoms, not one. Had he known, he would have doubled his estimate to a more accurate 14. This error was corrected in 1811 by Amedeo Avogadro. Avogadro proposed that equal volumes of any two gases, at equal temperature and pressure, contain equal numbers of molecules (in other words, the mass of a gas's particles does not affect the volume that it occupies). Avogadro's hypothesis, now usually called Avogadro's law, provided a method for deducing the relative weights of the molecules of gaseous elements, for if the hypothesis is correct relative gas densities directly indicate the relative weights of the particles that compose the gases. This way of thinking led directly to a second hypothesis: the particles of certain elemental gases were pairs of atoms, and when reacting chemically these molecules often split in two. For instance, the fact that two liters of hydrogen will react with just one liter of oxygen to produce two liters of water vapor (at constant pressure and temperature) suggested that a single oxygen molecule splits in two in order to form two molecules of water. The formula of water is H2O, not HO. Avogadro measured oxygen's atomic weight to be 15.074. | History of atomic theory | Wikipedia | 392 | 2844 | https://en.wikipedia.org/wiki/History%20of%20atomic%20theory | Physical sciences | Atomic physics | null |
Opposition to atomic theory
Dalton's atomic theory attracted widespread interest but not everyone accepted it at first. The law of multiple proportions was shown not to be a universal law when it came to organic substances, whose molecules can be quite large. For instance, in oleic acid there is 34 g of hydrogen for every 216 g of carbon, and in methane there is 72 g of hydrogen for every 216 g of carbon. 34 and 72 form a ratio of 17:36, which is not a ratio of small whole numbers. We know now that carbon-based substances can have very large molecules, larger than any the other elements can form. Oleic acid's formula is C18H34O2 and methane's is CH4. The law of multiple proportions by itself was not complete proof, and atomic theory was not universally accepted until the end of the 19th century.
One problem was the lack of uniform nomenclature. The word "atom" implied indivisibility, but Dalton defined an atom as being the ultimate particle of any chemical substance, not just the elements or even matter per se. This meant that "compound atoms" such as carbon dioxide could be divided, as opposed to "elementary atoms". Dalton disliked the word "molecule", regarding it as "diminutive". Amedeo Avogadro did the opposite: he exclusively used the word "molecule" in his writings, eschewing the word "atom", instead using the term "elementary molecule". Jöns Jacob Berzelius used the term "organic atoms" to refer to particles containing three or more elements, because he thought this only existed in organic compounds. Jean-Baptiste Dumas used the terms "physical atoms" and "chemical atoms"; a "physical atom" was a particle that cannot be divided by physical means such as temperature and pressure, and a "chemical atom" was a particle that could not be divided by chemical reactions.
The modern definitions of atom and molecule—an atom being the basic particle of an element, and a molecule being an agglomeration of atoms—were established in the late half of the 19th century. A key event was the Karlsruhe Congress in Germany in 1860. As the first international congress of chemists, its goal was to establish some standards in the community. A major proponent of the modern distinction between atoms and molecules was Stanislao Cannizzaro. | History of atomic theory | Wikipedia | 485 | 2844 | https://en.wikipedia.org/wiki/History%20of%20atomic%20theory | Physical sciences | Atomic physics | null |
Cannizzaro criticized past chemists such as Berzelius for not accepting that the particles of certain gaseous elements are actually pairs of atoms, which led to mistakes in their formulation of certain compounds. Berzelius believed that hydrogen gas and chlorine gas particles are solitary atoms. But he observed that when one liter of hydrogen reacts with one liter of chlorine, they form two liters of hydrogen chloride instead of one. Berzelius decided that Avogadro's law does not apply to compounds. Cannizzaro preached that if scientists just accepted the existence of single-element molecules, such discrepancies in their findings would be easily resolved. But Berzelius did not even have a word for that. Berzelius used the term "elementary atom" for a gas particle which contained just one element and "compound atom" for particles which contained two or more elements, but there was nothing to distinguish H2 from H since Berzelius did not believe in H2. So Cannizzaro called for a redefinition so that scientists could understand that a hydrogen molecule can split into two hydrogen atoms in the course of a chemical reaction.
A second objection to atomic theory was philosophical. Scientists in the 19th century had no way of directly observing atoms. They inferred the existence of atoms through indirect observations, such as Dalton's law of multiple proportions. Some scientists adopted positions aligned with the philosophy of positivism, arguing that scientists should not attempt to deduce the deeper reality of the universe, but only systemize what patterns they could directly observe.
This generation of anti-atomists can be grouped in two camps.
The "equivalentists", like Marcellin Berthelot, believed the theory of equivalent weights was adequate for scientific purposes. This generalization of Proust's law of definite proportions summarized observations. For example, 1 gram of hydrogen will combine with 8 grams of oxygen to form 9 grams of water, therefore the "equivalent weight" of oxygen is 8 grams. The "energeticist", like Ernst Mach and Wilhelm Ostwald, were philosophically opposed to hypothesis about reality altogether. In their view, only energy as part of thermodynamics should be the basis of physical models.
These positions were eventually quashed by two important advancements that happened later in the 19th century: the development of the periodic table and the discovery that molecules have an internal architecture that determines their properties. | History of atomic theory | Wikipedia | 503 | 2844 | https://en.wikipedia.org/wiki/History%20of%20atomic%20theory | Physical sciences | Atomic physics | null |
Isomerism
Scientists discovered some substances have the exact same chemical content but different properties. For instance, in 1827, Friedrich Wöhler discovered that silver fulminate and silver cyanate are both 107 parts silver, 12 parts carbon, 14 parts nitrogen, and 16 parts oxygen (we now know their formulas as both AgCNO). In 1830 Jöns Jacob Berzelius introduced the term isomerism to describe the phenomenon. In 1860, Louis Pasteur hypothesized that the molecules of isomers might have the same set of atoms but in different arrangements.
In 1874, Jacobus Henricus van 't Hoff proposed that the carbon atom bonds to other atoms in a tetrahedral arrangement. Working from this, he explained the structures of organic molecules in such a way that he could predict how many isomers a compound could have. Consider, for example, pentane (C5H12). In van 't Hoff's way of modelling molecules, there are three possible configurations for pentane, and scientists did go on to discover three and only three isomers of pentane.
Isomerism was not something that could be fully explained by alternative theories to atomic theory, such as radical theory and the theory of types.
Mendeleev's periodic table
Dmitrii Mendeleev noticed that when he arranged the elements in a row according to their atomic weights, there was a certain periodicity to them. For instance, the second element, lithium, had similar properties to the ninth element, sodium, and the sixteenth element, potassium — a period of seven. Likewise, beryllium, magnesium, and calcium were similar and all were seven places apart from each other on Mendeleev's table. Using these patterns, Mendeleev predicted the existence and properties of new elements, which were later discovered in nature: scandium, gallium, and germanium. Moreover, the periodic table could predict how many atoms of other elements that an atom could bond with — e.g., germanium and carbon are in the same group on the table and their atoms both combine with two oxygen atoms each (GeO2 and CO2). Mendeleev found these patterns validated atomic theory because it showed that the elements could be categorized by their atomic weight. Inserting a new element into the middle of a period would break the parallel between that period and the next, and would also violate Dalton's law of multiple proportions. | History of atomic theory | Wikipedia | 505 | 2844 | https://en.wikipedia.org/wiki/History%20of%20atomic%20theory | Physical sciences | Atomic physics | null |
The elements on the periodic table were originally arranged in order of increasing atomic weight. However, in a number of places chemists chose to swap the positions of certain adjacent elements so that they appeared in a group with other elements with similar properties. For instance, tellurium is placed before iodine even though tellurium is heavier (127.6 vs 126.9) so that iodine can be in the same column as the other halogens. The modern periodic table is based on atomic number, which is equivalent to the nuclear charge, a change had to wait for the discovery of the nucleus.
In addition, an entire row of the table was not shown
because the noble gases had not been discovered when Mendeleev devised his table.
Statistical mechanics
In 1738, Swiss physicist and mathematician Daniel Bernoulli postulated that the pressure of gases and heat were both caused by the underlying motion of particles. Using his model he could predict the ideal gas law at constant temperature and suggested that the temperature was proportional to the velocity of the particles. These results were largely ignored for a century.
James Clerk Maxwell, a vocal proponent of atomism, revived the kinetic theory in 1860 and 1867. His key insight was that the velocity of particles in a gas would vary around an average value, introducing the concept of a distribution function. Ludwig Boltzmann and Rudolf Clausius expanded his work on gases and the laws of thermodynamics especially the second law relating to entropy. In the 1870s, Josiah Willard Gibbs extended the laws of entropy and thermodynamics and coined the term "statistical mechanics."
Boltzmann defended the atomistic hypothesis against major detractors from the time like Ernst Mach or energeticists like Wilhelm Ostwald, who considered that energy was the elementary quantity of reality.
At the beginning of the 20th century, Albert Einstein independently reinvented Gibbs' laws, because they had only been printed in an obscure American journal. Einstein later commented that had he known of Gibbs' work, he would "not have published those papers at all, but confined myself to the treatment of some few points [that were distinct]." All of statistical mechanics and the laws of heat, gas, and entropy took the existence of atoms as a necessary postulate. | History of atomic theory | Wikipedia | 456 | 2844 | https://en.wikipedia.org/wiki/History%20of%20atomic%20theory | Physical sciences | Atomic physics | null |
Brownian motion
In 1827, the British botanist Robert Brown observed that dust particles inside pollen grains floating in water constantly jiggled about for no apparent reason. In 1905, Einstein theorized that this Brownian motion was caused by the water molecules continuously knocking the grains about, and developed a mathematical model to describe it. This model was validated experimentally in 1908 by French physicist Jean Perrin, who used Einstein's equations to measure the size of atoms.
Discovery of the electron
Atoms were thought to be the smallest possible division of matter until 1899 when J. J. Thomson discovered the electron through his work on cathode rays.
A Crookes tube is a sealed glass container in which two electrodes are separated by a vacuum. When a voltage is applied across the electrodes, cathode rays are generated, creating a glowing patch where they strike the glass at the opposite end of the tube. Through experimentation, Thomson discovered that the rays could be deflected by electric fields and magnetic fields, which meant that these rays were not a form of light but were composed of very light charged particles, and their charge was negative. Thomson called these particles "corpuscles". He measured their mass-to-charge ratio to be several orders of magnitude smaller than that of the hydrogen atom, the smallest atom. This ratio was the same regardless of what the electrodes were made of and what the trace gas in the tube was.
In contrast to those corpuscles, positive ions created by electrolysis or X-ray radiation had mass-to-charge ratios that varied depending on the material of the electrodes and the type of gas in the reaction chamber, indicating they were different kinds of particles. | History of atomic theory | Wikipedia | 339 | 2844 | https://en.wikipedia.org/wiki/History%20of%20atomic%20theory | Physical sciences | Atomic physics | null |
In 1898, Thomson measured the charge on ions to be roughly 6 × 10−10 electrostatic units (2 × 10−19 Coulombs). In 1899, he showed that negative electricity created by ultraviolet light landing on a metal (known now as the photoelectric effect) has the same mass-to-charge ratio as cathode rays; then he applied his previous method for determining the charge on ions to the negative electric particles created by ultraviolet light. By this combination he showed that electron's mass was 0.0014 times that of hydrogen ions. These "corpuscles" were so light yet carried so much charge that Thomson concluded they must be the basic particles of electricity, and for that reason other scientists decided that these "corpuscles" should instead be called electrons following an 1894 suggestion by George Johnstone Stoney for naming the basic unit of electrical charge.
In 1904, Thomson published a paper describing a new model of the atom. Electrons reside within atoms, and they transplant themselves from one atom to the next in a chain in the action of an electrical current. When electrons do not flow, their negative charge logically must be balanced out by some source of positive charge within the atom so as to render the atom electrically neutral. Having no clue as to the source of this positive charge, Thomson tentatively proposed that the positive charge was everywhere in the atom, the atom being shaped like a sphere—this was the mathematically simplest model to fit the available evidence (or lack of it). The balance of electrostatic forces would distribute the electrons throughout this sphere in a more or less even manner. Thomson further explained that ions are atoms that have a surplus or shortage of electrons.
Thomson's model is popularly known as the plum pudding model, based on the idea that the electrons are distributed throughout the sphere of positive charge with the same density as raisins in a plum pudding. Neither Thomson nor his colleagues ever used this analogy. It seems to have been a conceit of popular science writers. The analogy suggests that the positive sphere is like a solid, but Thomson likened it to a liquid, as he proposed that the electrons moved around in it in patterns governed by the electrostatic forces. More to the point, the positive electrification in Thomson's model was an abstraction, he did not propose anything concrete like a particle. Thomson's model was incomplete, it could not predict any of the known properties of the atom such as emission spectra or valencies. | History of atomic theory | Wikipedia | 497 | 2844 | https://en.wikipedia.org/wiki/History%20of%20atomic%20theory | Physical sciences | Atomic physics | null |
In 1906, Robert A. Millikan and Harvey Fletcher performed the oil drop experiment in which they measured the charge of an electron to be about -1.6 × 10−19, a value now defined as -1 e. Since the hydrogen ion and the electron were known to be indivisible and a hydrogen atom is neutral in charge, it followed that the positive charge in hydrogen was equal to this value, i.e. 1 e.
Discovery of the nucleus
Thomson's plum pudding model was challenged in 1911 by one of his former students, Ernest Rutherford, who presented a new model to explain new experimental data. The new model proposed a concentrated center of charge and mass that was later dubbed the atomic nucleus.
Ernest Rutherford and his colleagues Hans Geiger and Ernest Marsden came to have doubts about the Thomson model after they encountered difficulties when they tried to build an instrument to measure the charge-to-mass ratio of alpha particles (these are positively-charged particles emitted by certain radioactive substances such as radium). The alpha particles were being scattered by the air in the detection chamber, which made the measurements unreliable. Thomson had encountered a similar problem in his work on cathode rays, which he solved by creating a near-perfect vacuum in his instruments. Rutherford didn't think he'd run into this same problem because alpha particles usually have much more momentum than electrons. According to Thomson's model of the atom, the positive charge in the atom is not concentrated enough to produce an electric field strong enough to deflect an alpha particle. Yet there was scattering, so Rutherford and his colleagues decided to investigate this scattering carefully. | History of atomic theory | Wikipedia | 331 | 2844 | https://en.wikipedia.org/wiki/History%20of%20atomic%20theory | Physical sciences | Atomic physics | null |
Between 1908 and 1913, Rutherford and his colleagues performed a series of experiments in which they bombarded thin foils of metal with a beam of alpha particles. They spotted alpha particles being deflected by angles greater than 90°. According to Thomson's model, all of the alpha particles should have passed through with negligible deflection. Rutherford deduced that the positive charge of the atom is not distributed throughout the atom's volume as Thomson believed, but is concentrated in a tiny nucleus at the center. This nucleus also carries most of the atom's mass. Only such an intense concentration of charge, anchored by its high mass, could produce an electric field strong enough to deflect the alpha particles as observed. Rutherford's model, being supported primarily by scattering data unfamiliar to many scientists, did not catch on until Niels Bohr joined Rutherford's lab and developed a new model for the electrons.
Rutherford model predicted that the scattering of alpha particles would be proportional to the square of the atomic charge. Geiger and Marsden's based their analysis on setting the charge to half of the atomic weight of the foil's material (gold, aluminium, etc.). Amateur physicist Antonius van den Broek noted that there was a more precise relation between the charge and the element's numeric sequence in the order of atomic weights. The sequence number came be called the atomic number and it replaced atomic weight in organizing the periodic table.
Bohr model
Rutherford deduced the existence of the atomic nucleus through his experiments but he had nothing to say about how the electrons were arranged around it. In 1912, Niels Bohr joined Rutherford's lab and began his work on a quantum model of the atom. | History of atomic theory | Wikipedia | 348 | 2844 | https://en.wikipedia.org/wiki/History%20of%20atomic%20theory | Physical sciences | Atomic physics | null |
Max Planck in 1900 and Albert Einstein in 1905 had postulated that light energy is emitted or absorbed in discrete amounts known as quanta (singular, quantum). This led to a series of atomic models with some quantum aspects, such as that of Arthur Erich Haas in 1910 and the 1912 John William Nicholson atomic model with quantized angular momentum as h/2. The dynamical structure of these models was still classical, but in 1913, Bohr abandon the classical approach. He started his Bohr model of the atom with a quantum hypothesis: an electron could only orbit the nucleus in particular circular orbits with fixed angular momentum and energy, its distance from the nucleus (i.e., their radii) being proportional to its energy. Under this model an electron could not lose energy in a continuous manner; instead, it could only make instantaneous "quantum leaps" between the fixed energy levels. When this occurred, light was emitted or absorbed at a frequency proportional to the change in energy (hence the absorption and emission of light in discrete spectra).
In a trilogy of papers Bohr described and applied his model to derive the Balmer series of lines in the atomic spectrum of hydrogen and the related spectrum of He+. He also used he model to describe the structure of the periodic table and aspects of chemical bonding. Together these results lead to Bohr's model being widely accepted by the end of 1915.
Bohr's model was not perfect. It could only predict the spectral lines of hydrogen, not those of multielectron atoms. Worse still, it could not even account for all features of the hydrogen spectrum: as spectrographic technology improved, it was discovered that applying a magnetic field caused spectral lines to multiply in a way that Bohr's model couldn't explain. In 1916, Arnold Sommerfeld added elliptical orbits to the Bohr model to explain the extra emission lines, but this made the model very difficult to use, and it still couldn't explain more complex atoms.
Discovery of isotopes
While experimenting with the products of radioactive decay, in 1913 radiochemist Frederick Soddy discovered that there appeared to be more than one variety of some elements. The term isotope was coined by Margaret Todd as a suitable name for these varieties. | History of atomic theory | Wikipedia | 455 | 2844 | https://en.wikipedia.org/wiki/History%20of%20atomic%20theory | Physical sciences | Atomic physics | null |
That same year, J. J. Thomson conducted an experiment in which he channeled a stream of neon ions through magnetic and electric fields, striking a photographic plate at the other end. He observed two glowing patches on the plate, which suggested two different deflection trajectories. Thomson concluded this was because some of the neon ions had a different mass. The nature of this differing mass would later be explained by the discovery of neutrons in 1932: all atoms of the same element contain the same number of protons, while different isotopes have different numbers of neutrons.
Discovery of the proton
Back in 1815, William Prout observed that the atomic weights of the known elements were multiples of hydrogen's atomic weight, so he hypothesized that all atoms are agglomerations of hydrogen, a particle which he dubbed "the protyle". Prout's hypothesis was put into doubt when some elements were found to deviate from this pattern—e.g. chlorine atoms on average weigh 35.45 daltons—but when isotopes were discovered in 1913, Prout's observation gained renewed attention.
In 1898, J. J. Thomson found that the positive charge of a hydrogen ion was equal to the negative charge of a single electron.
In an April 1911 paper concerning his studies on alpha particle scattering, Ernest Rutherford estimated that the charge of an atomic nucleus, expressed as a multiplier of hydrogen's nuclear charge (qe), is roughly half the atom's atomic weight.
In June 1911, Van den Broek noted that on the periodic table, each successive chemical element increased in atomic weight on average by 2, which in turn suggested that each successive element's nuclear charge increased by 1 qe. In 1913, van den Broek further proposed that the electric charge of an atom's nucleus, expressed as a multiplier of the elementary charge, is equal to the element's sequential position on the periodic table. Rutherford defined this position as being the element's atomic number.
In 1913, Henry Moseley measured the X-ray emissions of all the elements on the periodic table and found that the frequency of the X-ray emissions was a mathematical function of the element's atomic number and the charge of a hydrogen nucleus .
In 1917 Rutherford bombarded nitrogen gas with alpha particles and observed hydrogen ions being emitted from the gas. Rutherford concluded that the alpha particles struck the nuclei of the nitrogen atoms, causing hydrogen ions to split off. | History of atomic theory | Wikipedia | 507 | 2844 | https://en.wikipedia.org/wiki/History%20of%20atomic%20theory | Physical sciences | Atomic physics | null |
These observations led Rutherford to conclude that the hydrogen nucleus was a singular particle with a positive charge equal to that of the electron's negative charge. The name "proton" was suggested by Rutherford at an informal meeting of fellow physicists in Cardiff in 1920.
The charge number of an atomic nucleus was found to be equal to the element's ordinal position on the periodic table. The nuclear charge number thus provided a simple and clear-cut way of distinguishing the chemical elements from each other, as opposed to Lavoisier's classic definition of a chemical element being a substance that cannot be broken down into simpler substances by chemical reactions. The charge number or proton number was thereafter referred to as the atomic number of the element. In 1923, the International Committee on Chemical Elements officially declared the atomic number to be the distinguishing quality of a chemical element.
During the 1920s, some writers defined the atomic number as being the number of "excess protons" in a nucleus. Before the discovery of the neutron, scientists believed that the atomic nucleus contained a number of "nuclear electrons" which cancelled out the positive charge of some of its protons. This explained why the atomic weights of most atoms were higher than their atomic numbers. Helium, for instance, was thought to have four protons and two nuclear electrons in the nucleus, leaving two excess protons and a net nuclear charge of 2+. After the neutron was discovered, scientists realized the helium nucleus in fact contained two protons and two neutrons.
Discovery of the neutron
Physicists in the 1920s believed that the atomic nucleus contained protons plus a number of "nuclear electrons" that reduced the overall charge. These "nuclear electrons" were distinct from the electrons that orbited the nucleus. This incorrect hypothesis would have explained why the atomic numbers of the elements were less than their atomic weights, and why radioactive elements emit electrons (beta radiation) in the process of nuclear decay. Rutherford even hypothesized that a proton and an electron could bind tightly together into a "neutral doublet". Rutherford wrote that the existence of such "neutral doublets" moving freely through space would provide a more plausible explanation for how the heavier elements could have formed in the genesis of the Universe, given that it is hard for a lone proton to fuse with a large atomic nucleus because of the repulsive electric field. | History of atomic theory | Wikipedia | 472 | 2844 | https://en.wikipedia.org/wiki/History%20of%20atomic%20theory | Physical sciences | Atomic physics | null |
In 1928, Walter Bothe observed that beryllium emitted a highly penetrating, electrically neutral radiation when bombarded with alpha particles. It was later discovered that this radiation could knock hydrogen atoms out of paraffin wax. Initially it was thought to be high-energy gamma radiation, since gamma radiation had a similar effect on electrons in metals, but James Chadwick found that the ionization effect was too strong for it to be due to electromagnetic radiation, so long as energy and momentum were conserved in the interaction. In 1932, Chadwick exposed various elements, such as hydrogen and nitrogen, to the mysterious "beryllium radiation", and by measuring the energies of the recoiling charged particles, he deduced that the radiation was actually composed of electrically neutral particles which could not be massless like the gamma ray, but instead were required to have a mass similar to that of a proton. Chadwick called this new particle "the neutron" and believed that it to be a proton and electron fused together because the neutron had about the same mass as a proton and an electron's mass is negligible by comparison. Neutrons are not in fact a fusion of a proton and an electron.
Modern quantum mechanical models
In 1924, Louis de Broglie proposed that all particles—particularly subatomic particles such as electrons—have an associated wave. Erwin Schrödinger, fascinated by this idea, developed an equation that describes an electron as a wave function instead of a point. This approach predicted many of the spectral phenomena that Bohr's model failed to explain, but it was difficult to visualize, and faced opposition. One of its critics, Max Born, proposed instead that Schrödinger's wave function did not describe the physical extent of an electron (like a charge distribution in classical electromagnetism), but rather gave the probability that an electron would, when measured, be found at a particular point. This reconciled the ideas of wave-like and particle-like electrons: the behavior of an electron, or of any other subatomic entity, has both wave-like and particle-like aspects, and whether one aspect or the other is observed depend upon the experiment.
A consequence of describing particles as waveforms rather than points is that it is mathematically impossible to calculate with precision both the position and momentum of a particle at a given point in time. This became known as the uncertainty principle, a concept first introduced by Werner Heisenberg in 1927. | History of atomic theory | Wikipedia | 498 | 2844 | https://en.wikipedia.org/wiki/History%20of%20atomic%20theory | Physical sciences | Atomic physics | null |
Schrödinger's wave model for hydrogen replaced Bohr's model, with its neat, clearly defined circular orbits. The modern model of the atom describes the positions of electrons in an atom in terms of probabilities. An electron can potentially be found at any distance from the nucleus, but, depending on its energy level and angular momentum, exists more frequently in certain regions around the nucleus than others; this pattern is referred to as its atomic orbital. The orbitals come in a variety of shapes—sphere, dumbbell, torus, etc.—with the nucleus in the middle. The shapes of atomic orbitals are found by solving the Schrödinger equation. Analytic solutions of the Schrödinger equation are known for very few relatively simple model Hamiltonians including the hydrogen atom and the hydrogen molecular ion. Beginning with the helium atom—which contains just two electrons—numerical methods are used to solve the Schrödinger equation.
Qualitatively the shape of the atomic orbitals of multi-electron atoms resemble the states of the hydrogen atom. The Pauli principle requires the distribution of these electrons within the atomic orbitals such that no more than two electrons are assigned to any one orbital; this requirement profoundly affects the atomic properties and ultimately the bonding of atoms into molecules. | History of atomic theory | Wikipedia | 261 | 2844 | https://en.wikipedia.org/wiki/History%20of%20atomic%20theory | Physical sciences | Atomic physics | null |
An anxiolytic (; also antipanic or anti-anxiety agent) is a medication or other intervention that reduces anxiety. This effect is in contrast to anxiogenic agents which increase anxiety. Anxiolytic medications are used for the treatment of anxiety disorders and their related psychological and physical symptoms.
Nature of anxiety
Anxiety is a naturally-occurring emotion and response. When anxiety levels exceed the tolerability of a person, anxiety disorders may occur. People with anxiety disorders can exhibit fear responses, such as defensive behaviors, high levels of alertness, and negative emotions. Those with anxiety disorders may have concurrent psychological disorders, such as depression. Anxiety disorders are classified using six possible clinical assessments:
Different types of anxiety disorders will share some general symptoms while having their own distinctive symptoms. This explains why people with different types of anxiety disorders will respond differently to different classes of anti-anxiety medications.
Etiology
The etiology of anxiety disorder remains unknown. There are several contributing factors that are still yet to be proved to cause anxiety disorders. These factors include childhood anxiety, drug induction by central stimulant drugs, metabolic diseases or having depressive disorder.
Medications
Anti-anxiety medication is any drug that can be taken or prescribed for the treatment of anxiety disorders, which may be mediated by neurotransmitters like norepinephrine, serotonin, dopamine, and gamma-aminobutyric acid (GABA) in the central nervous system. Anti-anxiety medication can be classified into six types according to their different mechanisms: antidepressants, benzodiazepines, azapirones, antiepileptics, antipsychotics, and beta blockers. | Anxiolytic | Wikipedia | 345 | 2869 | https://en.wikipedia.org/wiki/Anxiolytic | Biology and health sciences | Psychiatric drugs | Health |
Antidepressants include selective serotonin reuptake inhibitors (SSRIs), serotonin–norepinephrine reuptake inhibitors (SNRIs), tricyclic antidepressants (TCAs), and monoamine oxidase inhibitors (MAOIs). SSRIs are used in all types of anxiety disorders while SNRIs are used for generalized anxiety disorder (GAD). Both of them are considered as first-line anti-anxiety medications. TCAs are second-line treatment as they cause more significant adverse effects when compared to the first-line treatment. Benzodiazepines are effective in emergent and short-term treatment of anxiety disorders due to their fast onset but carry the risk of dependence. Buspirone is indicated for GAD, which has much slower onset but with the advantage of less sedating and withdrawal effects.
History
The first monoamine oxidase inhibitor (MAOI), iproniazid, was discovered accidentally when developing the new antitubercular drug isoniazid. The drug was found to induce euphoria and improve the patient's appetite and sleep quality.
The first tricyclic antidepressant, imipramine, was originally developed and studied to be an antihistamine alongside other first-generation antihistamines of the time, such as promethazine. TCAs can increase the level of norepinephrine and serotonin by inhibiting their reuptake transport proteins. The majority of TCAs exert greater effect on norepinephrine, which leads to side effects like drowsiness and memory loss.
In order to be more effective on serotonin agonism and avoid anticholinergic and antihistaminergic side effects, selective serotonin reuptake inhibitors (SSRI) were researched and introduced to treat anxiety disorders. The first SSRI, fluoxetine (Prozac), was discovered in 1974 and approved by FDA in 1987. After that, other SSRIs like sertraline (Zoloft), paroxetine (Paxil), and escitalopram (Lexapro) have entered the market. | Anxiolytic | Wikipedia | 456 | 2869 | https://en.wikipedia.org/wiki/Anxiolytic | Biology and health sciences | Psychiatric drugs | Health |
The first serotonin norepinephrine reuptake inhibitor (SNRI), venlafaxine (Effexor), entered the market in 1993. SNRIs can target serotonin and norepinephrine transporters while avoiding imposing significant effects on other adrenergic (α1, α2, and β), histamine (H1), muscarinic, dopamine, or postsynaptic serotonin receptors.
Classifications
There are six groups of anti-anxiety medications available that have been proven to be clinically significant in treatment of anxiety disorders. The groups of medications are as follows.
Antidepressants
Medications that are indicated for both anxiety disorders and depression. Selective serotonin reuptake inhibitors (SSRIs) and serotonin–norepinephrine reuptake inhibitors (SNRIs) are new generations of antidepressants. They have a much lower adverse effect profile than older antidepressants like monoamine oxidase inhibitors (MAOIs) and tricyclic antidepressants (TCAs). Therefore, SSRIs and SNRIs are now the first-line agent in treating long term anxiety disorders, given their applications and significance in all six types of disorders.
Benzodiazepines
Benzodiazepines are used for acute anxiety and could be added along with current use of SSRIs to stabilize a treatment. Long-term use in treatment plans is not recommended. Different kinds of benzodiazepine will vary in its pharmacological profile, including its strength of effect and time taken for metabolism. The choice of the benzodiazepine will depend on the corresponding profiles.
Benzodiazepines are used for emergent or short-term management. They are not recommended as the first-line anti-anxiety drugs, but they can be used in combination with SSRIs/SNRIs during the initial treatment stage. Indications include panic disorder, sleep disorders, seizures, acute behavioral disturbance, muscle spasm and premedication and sedation for procedures.
Azapirones
Buspirone can be useful in GAD but not particularly effective in treating phobias, panic disorder or social anxiety disorders. It is a safer option for long-term use as it does not cause dependence like benzodiazepines. | Anxiolytic | Wikipedia | 485 | 2869 | https://en.wikipedia.org/wiki/Anxiolytic | Biology and health sciences | Psychiatric drugs | Health |
Antiepileptics
Antiepileptics are rarely prescribed as an off-label treatment for anxiety disorders and post-traumatic stress disorders. There have been some suggestions that they may help with anxiety symptoms but there is generally a lack of research on its use.
One antiepileptic, pregabalin, has been found to be better at treating GAD than a placebo, and comparable effects to benzodiazepines. It has also been shown be potentially efficient in treating social anxiety disorder. Gabapentin has been prescribed off-label for anxiety despite a lack of research evidence supporting such use, although some studies have indicated that it may relieve anxiety symptoms. The potential anxiolytic effect of tiagabine has been observed in some pre-clinical trials, but its effectiveness has not yet been proved. Similarly, there is a lack of research on valproate for the treatment of anxiety disorders.
Antipsychotics
Olanzapine and risperidone are atypical antipsychotics which are also effective in GAD and PTSD treatment. However, there is a higher chance of experiencing adverse effects than the other anti-anxiety medications.
Beta-adrenoceptor antagonists
Propranolol is originally used for high blood pressure and heart diseases. It can also be used to treat anxiety with symptoms like tremor or increased heart rate. They work on the nervous system and alleviate the symptoms as a relief. Propranolol is also commonly used for public speaking when one is nervous.
Mechanism of action | Anxiolytic | Wikipedia | 312 | 2869 | https://en.wikipedia.org/wiki/Anxiolytic | Biology and health sciences | Psychiatric drugs | Health |
SSRIs and SNRIs
Both selective serotonin reuptake inhibitors (SSRI) and serotonin and norepinephrine reuptake inhibitors (SNRI) are reuptake inhibitors of a class of nerve signal transduction chemical called neurotransmitters. Serotonin and norepinephrine are neurotransmitters that are related to nervous control in mood regulation. The level of these neurotransmitters is regulated by the nerve through reuptake to avoid accumulation of the neurotransmitter at the endings of nerve fibers. By reuptaking the neurotransmitter, the level of neuronal activity will go back down and be ready to go back up upon excitation from a new nerve signal. However the neurotransmitter level of patients with anxiety disorders is usually low or the patients’ nerve fibers are insensitive to the neurotransmitters. SSRIs and SNRIs will then block the channel of reuptake and increase the level of the neurotransmitter. The nerve fibers will inhibit further production of neurotransmitters upon the increase. However the prolonged increase will eventually desensitize the nerve about the change in level. Therefore, the action of both SSRIs and SNRIs will take 4–6 weeks to exert their full effect.
Benzodiazepine
Benzodiazepines bind selectively to the GABA receptor, which is the receptor protein found in the nervous system and is in control of the nervous response. Benzodiazepine will increase the entry of chloride ions into the cells by improving the binding between GABA and GABA receptors and then the better opening of the channel for chloride ion passage. The high level of chloride ion inside the nerve cells makes the nerve more difficult to depolarize and inhibit further nerve signal transduction. The excitability of the nerves then reduces and the nervous system slows down. Therefore, the drug can alleviate symptoms of anxiety disorder and make the person less nervous.
Clinical use | Anxiolytic | Wikipedia | 430 | 2869 | https://en.wikipedia.org/wiki/Anxiolytic | Biology and health sciences | Psychiatric drugs | Health |
Selective serotonin reuptake inhibitors
Selective serotonin reuptake inhibitors (SSRIs) are a class of medications used in the treatment of depression, anxiety disorders, OCD and some personality disorders. SSRIs are the first-line anti-anxiety medications. Serotonin is one of the crucial neurotransmitters in mood enhancement, and increasing serotonin level produces an anti-anxiety effect. SSRIs increase the serotonin level in the brain by inhibiting serotonin uptake pumps on serotonergic systems, without interactions with other receptors and ion channels. SSRIs are beneficial in both acute response and long-term maintenance treatment for both depression and anxiety disorder.
SSRIs can increase anxiety initially due to negative feedback through the serotonergic autoreceptors; for this reason a concurrent benzodiazepine can be used until the anxiolytic effect of the SSRI occurs.
The SSRIs paroxetine and escitalopram are USFDA approved to treat generalized anxiety disorder.
Therapeutic use
Adverse effect
The common early side effects of SSRIs include nausea and loose stool, which can be solved by discontinuing the treatment. Headache, dizziness, insomnia are the common early side effects as well.
Sexual dysfunction, anorgasmia, erectile dysfunction, and reduced libido are common adverse side effects of SSRIs. Sometimes they may persist after the cessation of treatment.
Withdrawal symptoms like dizziness, headache and flu-like symptoms (fatigue/myalgia/loose stool) may occur if SSRI is stopped suddenly. The brain is incapable of upregulating the receptors to sufficient levels especially after discontinuation of the drugs with short half life like paroxetine. Both fluoxetine and its active metabolite have a long half life therefore it causes the least withdrawal symptoms.
Serotonin–norepinephrine reuptake inhibitors
Serotonin–norepinephrine reuptake inhibitor (SNRIs) include venlafaxine and duloxetine drugs. Venlafaxine, in extended release form, and duloxetine, are indicated for the treatment of GAD. SNRIs are as effective as SSRIs in the treatment of anxiety disorders. | Anxiolytic | Wikipedia | 475 | 2869 | https://en.wikipedia.org/wiki/Anxiolytic | Biology and health sciences | Psychiatric drugs | Health |
Tricyclic antidepressants
Tricyclic antidepressants (TCAs) have anxiolytic effects; however, side effects are often more troubling or severe and overdose is dangerous. They are considered effective, but have generally been replaced by antidepressants that cause different adverse effects. Examples include imipramine, doxepin, amitriptyline, nortriptyline and desipramine.
Therapeutic use
Contraindication
TCAs may cause drug poisoning in patients with hypotension, cardiovascular diseases and arrhythmias.
Tetracyclic antidepressants
Mirtazapine has demonstrated anxiolytic effect comparable to SSRIs while rarely causing or exacerbating anxiety. Mirtazapine's anxiety reduction tends to occur significantly faster than SSRIs.
Monoamine oxidase inhibitors
Monoamine oxidase inhibitors (MAOIs) are first-generation antidepressants effective for anxiety treatment but their dietary restrictions, adverse effect profile and availability of newer medications have limited their use. MAOIs include phenelzine, isocarboxazid and tranylcypromine. Pirlindole is a reversible MAOI that lacks dietary restriction.
Barbiturates
Barbiturates are powerful anxiolytics but the risk of abuse and addiction is high. Many experts consider these drugs obsolete for treating anxiety but valuable for the short-term treatment of severe insomnia, though only after benzodiazepines or non-benzodiazepines have failed.
Benzodiazepines
Benzodiazepines are prescribed to quell panic attacks. Benzodiazepines are also prescribed in tandem with an antidepressant for the latent period of efficacy associated with many ADs for anxiety disorder. There is risk of benzodiazepine withdrawal and rebound syndrome if BZDs are rapidly discontinued. Tolerance and dependence may occur. The risk of abuse in this class of medication is smaller than in that of barbiturates. Cognitive and behavioral adverse effects are possible. | Anxiolytic | Wikipedia | 430 | 2869 | https://en.wikipedia.org/wiki/Anxiolytic | Biology and health sciences | Psychiatric drugs | Health |
Benzodiazepines include:
alprazolam (Xanax), bromazepam,
chlordiazepoxide (Librium),
clonazepam (Klonopin),
diazepam (Valium),
lorazepam (Ativan),
oxazepam,
temazepam, and Triazolam.
Therapeutic use
Adverse effect
Benzodiazepines lead to central nervous system depression, resulting in common adverse effects like drowsiness, oversedation, light-headedness. Memory impairment can be a common adverse effect especially in elderly, hypersalivation, ataxia, slurred speech, psychomotor effects.
Sympatholytics
Sympatholytics are a group of anti-hypertensives which inhibit activity of the sympathetic nervous system. Beta blockers reduce anxiety by decreasing heart rate and preventing shaking. Beta blockers include propranolol, oxprenolol, and metoprolol. The alpha-1 antagonist prazosin could be effective for PTSD. The alpha-2 agonists clonidine and guanfacine have demonstrated both anxiolytic and anxiogenic effects.
Miscellaneous
Buspirone
Buspirone (Buspar) is a 5-HT1A receptor agonist used to treated generalized anxiety disorder. If an individual has only recently stopped taking benzodiazepines, buspirone will be less effective.
Pregabalin
Pregabalin (Lyrica) produces anxiolytic effect after one week of use comparable to lorazepam, alprazolam, and venlafaxine with more consistent psychic and somatic anxiety reduction. Unlike BZDs, it does not disrupt sleep architecture nor does it cause
cognitive or psychomotor impairment.
Hydroxyzine
Hydroxyzine (Atarax) is an antihistamine originally approved for clinical use by the FDA in 1956. Hydroxyzine has a calming effect which helps ameliorate anxiety. Hydroxyzine efficacy is comparable to benzodiazepines in the treatment of generalized anxiety disorder. | Anxiolytic | Wikipedia | 447 | 2869 | https://en.wikipedia.org/wiki/Anxiolytic | Biology and health sciences | Psychiatric drugs | Health |
Phenibut
Phenibut (Anvifen, Fenibut, Noofen) is an anxiolytic used in Russia. Phenibut is a GABAB receptor agonist, as well as an antagonist at α2δ subunit-containing voltage-dependent calcium channels (VDCCs), similarly to gabapentinoids like gabapentin and pregabalin. The medication is not approved by the FDA for use in the United States, but is sold online as a supplement.
Temgicoluril
Temgicoluril (Mebicar) is an anxiolytic produced in Latvia and used in Eastern Europe. Temgicoluril has an effect on the structure of limbic-reticular activity, particularly on the hypothalamus, as well as on all four basic neuromediator systems – γ aminobutyric acid (GABA), choline, serotonin and adrenergic activity. Temgicoluril decreases noradrenaline, increases serotonin, and exerts no effect on dopamine.
Fabomotizole
Fabomotizole (Afobazole) is an anxiolytic drug launched in Russia in the early 2000s. Its mechanism of action is poorly-defined, with GABAergic, NGF and BDNF release promoting, MT1 receptor agonism, MT3 receptor antagonism, and sigma receptor agonism thought to have some involvement.
Bromantane
Bromantane is a stimulant drug with anxiolytic properties developed in Russia during the late 1980s. Bromantane acts mainly by facilitating the biosynthesis of dopamine, through indirect genomic upregulation of relevant enzymes (tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AAAD)).
Emoxypine
Emoxypine is an antioxidant that is also a purported anxiolytic. Its chemical structure resembles that of pyridoxine, a form of vitamin B6.
Menthyl isovalerate
Menthyl isovalerate is a flavoring food additive marketed as a sedative and anxiolytic drug in Russia under the name Validol.
Racetams
Some racetam based drugs such as aniracetam can have an antianxiety effect. | Anxiolytic | Wikipedia | 500 | 2869 | https://en.wikipedia.org/wiki/Anxiolytic | Biology and health sciences | Psychiatric drugs | Health |
Alpidem
Alpidem is a nonbenzodiazepine anxiolytic with similar anxiolytic effectiveness as benzodiazepines but reduced sedation and cognitive, memory, and motor impairment. It was marketed briefly in France but was withdrawn from the market due to liver toxicity.
Etifoxine
Etifoxine has similar anxiolytic effects as benzodiazepine drugs, but does not produce the same levels of sedation and ataxia. Further, etifoxine does not affect memory and vigilance, and does not induce rebound anxiety, drug dependence, or withdrawal symptoms.
Alcohol
Alcohol is sometimes used as an anxiolytic by self-medication. fMRI can measure the anxiolytic effects of alcohol in the human brain.
Alternatives to medication
Cognitive behavioral therapy (CBT) is an effective treatment for panic disorder, social anxiety disorder, generalized anxiety disorder, and obsessive–compulsive disorder, while exposure therapy is the recommended treatment for anxiety related phobias. Healthcare providers can guide those with anxiety disorder by referring them to self-help resources. Sometimes medication is combined with psychotherapy but research has not found a benefit of combined pharmacotherapy and psychotherapy versus monotherapy.
If CBT is found ineffective, both the Canadian and American medical associations then suggest the use of medication. | Anxiolytic | Wikipedia | 277 | 2869 | https://en.wikipedia.org/wiki/Anxiolytic | Biology and health sciences | Psychiatric drugs | Health |
Antipsychotics, previously known as neuroleptics and major tranquilizers, are a class of psychotropic medication primarily used to manage psychosis (including delusions, hallucinations, paranoia or disordered thought), principally in schizophrenia but also in a range of other psychotic disorders. They are also the mainstay, together with mood stabilizers, in the treatment of bipolar disorder. Moreover, they are also used as adjuncts in the treatment of treatment-resistant major depressive disorder.
Use of antipsychotics is associated with reductions in brain tissue volumes, including white matter reduction, an effect which is dose-dependent and time-dependent. A recent controlled trial suggests that second generation antipsychotics combined with intensive psychosocial therapy may potentially prevent pallidal brain volume loss in first episode psychosis.
The use of antipsychotics may result in many unwanted side effects such as involuntary movement disorders, gynecomastia, impotence, weight gain and metabolic syndrome. Long-term use can produce adverse effects such as tardive dyskinesia, tardive dystonia, and tardive akathisia.
First-generation antipsychotics (e.g., chlorpromazine, haloperidol, etc.), known as typical antipsychotics, were first introduced in the 1950s, and others were developed until the early 1970s. Second-generation antipsychotics, known as atypical antipsychotics, arrived with the introduction of clozapine in the early 1970s followed by others (e.g., risperidone, olanzapine, etc.). Both generations of medication block receptors in the brain for dopamine, but atypicals block serotonin receptors as well. Third-generation antipsychotics were introduced in the 2000s and offer partial agonism, rather than blockade, of dopamine receptors. Neuroleptic, originating from (neuron) and (take hold of)—thus meaning "which takes the nerve"—refers to both common neurological effects and side effects. | Antipsychotic | Wikipedia | 437 | 2870 | https://en.wikipedia.org/wiki/Antipsychotic | Biology and health sciences | Psychiatric drugs | Health |
Medical uses
Antipsychotics are most frequently used for the following conditions:
Schizophrenia
Schizoaffective disorder most commonly in conjunction with either an antidepressant (in the case of the depressive subtype) or a mood stabilizer (in the case of the bipolar subtype). Antipsychotics possess mood stabilizing properties and thus they may be used as standalone medication to treat mood dysregulation.
Bipolar disorder (acute mania and mixed episodes) may be treated with either typical or atypical antipsychotics, although atypical antipsychotics are usually preferred because they tend to have more favourable adverse effect profiles and, according to a recent meta-analysis, they tend to have a lower liability for causing conversion from mania to depression.
Psychotic depression. In this indication it is a common practice for the psychiatrist to prescribe a combination of an atypical antipsychotic and an antidepressant as this practice is best supported by the evidence.
Treatment-resistant depression as an adjunct to standard antidepressant therapy.
Given the limited options available to treat the behavioral problems associated with dementia, other pharmacological and non-pharmacological interventions are usually attempted before using antipsychotics. A risk-to-benefit analysis is performed to weigh the risk of the adverse effects of antipsychotics versus: the potential benefit, the adverse effects of alternative interventions, and the risk of failing to intervene when a patient's behavior becomes unsafe. The same can be said for insomnia, in which they are not recommended as first-line therapy. There are evidence-based indications for using antipsychotics in children (e.g., tic disorder, bipolar disorder, psychosis), but the use of antipsychotics outside of those contexts (e.g., to treat behavioral problems) warrants significant caution.
Antipsychotics are used to treat tics associated with Tourette syndrome. Aripiprazole, an atypical antipsychotic, is used as add-on medication to ameliorate sexual dysfunction as a symptom of selective serotonin reuptake inhibitor (SSRI) antidepressants in women. Quetiapine is used to treat generalized anxiety disorder.
Schizophrenia | Antipsychotic | Wikipedia | 469 | 2870 | https://en.wikipedia.org/wiki/Antipsychotic | Biology and health sciences | Psychiatric drugs | Health |
Antipsychotic drug treatment is a key component of schizophrenia treatment recommendations by the National Institute of Health and Care Excellence (NICE), the American Psychiatric Association, and the British Society for Psychopharmacology. The main aim of treatment with antipsychotics is to reduce the positive symptoms of psychosis, that include delusions and hallucinations. There is mixed evidence to support a significant impact of antipsychotic use on primary negative symptoms (such as apathy, lack of emotional affect, and lack of interest in social interactions) or on cognitive symptoms (memory impairments, reduced ability to plan and execute tasks). In general, the efficacy of antipsychotic treatment in reducing positive symptoms appears to increase with the severity of baseline symptoms. All antipsychotic medications work relatively the same way: by antagonizing D2 dopamine receptors. However, there are some differences when it comes to typical and atypical antipsychotics. For example, atypical antipsychotic medications have been seen to lower the neurocognitive impairment associated with schizophrenia more than conventional antipsychotics, although the reasoning and mechanics of this are still unclear to researchers.
Applications of antipsychotic drugs in the treatment of schizophrenia include prophylaxis for those showing symptoms that suggest that they are at high risk of developing psychosis; treatment of first-episode psychosis; maintenance therapy (a form of prophylaxis, maintenance therapy aims to maintain therapeutic benefit and prevent symptom relapse); and treatment of recurrent episodes of acute psychosis. A recent 2024 study found that using high doses of antipsychotics for schizophrenia was linked to a higher risk of mortality. Researchers analyzed data from 32,240 individuals aged 17 to 64 diagnosed with schizophrenia between 2002 and 2012 to arrive at this conclusion. | Antipsychotic | Wikipedia | 375 | 2870 | https://en.wikipedia.org/wiki/Antipsychotic | Biology and health sciences | Psychiatric drugs | Health |
Prevention of psychosis and symptom improvement
Test batteries such as the PACE (Personal Assessment and Crisis Evaluation Clinic) and COPS (Criteria of Prodromal Syndromes), which measure low-level psychotic symptoms and cognitive disturbances, are used to evaluate people with early, low-level symptoms of psychosis. Test results are combined with family history information to identify patients in the "high-risk" group; they are considered to have a 20–40% risk of progression to frank psychosis within two years. These patients are often treated with low doses of antipsychotic drugs with the goal of reducing their symptoms and preventing progression to frank psychosis. While generally useful for reducing symptoms, clinical trials to date show little evidence that early use of antipsychotics improves long-term outcomes in those with prodromal symptoms, either alone or in combination with cognitive-behavioral therapy.
First-episode psychosis
First-episode psychosis (FEP) is the first time that psychotic symptoms are presented. NICE recommends that all people presenting with first-episode psychosis be treated with both an antipsychotic drug and cognitive behavioral therapy (CBT). NICE further recommends that those expressing a preference for CBT alone be informed that combination treatment is more effective. A diagnosis of schizophrenia is not made at this time as it takes longer to be determined by both DSM-5 and ICD-11, and only around 60% of those presenting with a first episode of psychosis will later be diagnosed with schizophrenia.
The conversion rate for a first episode of drug induced psychosis to bipolar disorder or schizophrenia is lower, with 30% of people converting to either bipolar disorder or schizophrenia. NICE makes no distinction between substance-induced psychosis and any other form of psychosis. The rate of conversion differs for different classes of drugs.
Pharmacological options for the specific treatment of FEP have been discussed in recent reviews. The goals of treatment for FEP include reducing symptoms and potentially improving long-term treatment outcomes. Randomized clinical trials have provided evidence for the efficacy of antipsychotic drugs in achieving the former goal, with first-generation and second generation antipsychotics showing about equal efficacy. The evidence that early treatment has a favorable effect on long-term outcomes is equivocal. | Antipsychotic | Wikipedia | 463 | 2870 | https://en.wikipedia.org/wiki/Antipsychotic | Biology and health sciences | Psychiatric drugs | Health |
Recurrent psychotic episodes
Placebo-controlled trials of both first- and second-generation antipsychotic drugs consistently demonstrate the superiority of active drugs over placebos in suppressing psychotic symptoms. A large meta-analysis of 38 trials of antipsychotic drugs in schizophrenia with acute psychotic episodes showed an effect size of about 0.5. There is little or no difference in efficacy among approved antipsychotic drugs, including both first- and second-generation agents. The efficacy of such drugs is suboptimal. Few patients achieve complete resolution of symptoms. Response rates, calculated using various cutoff values for symptom reduction, are low, and their interpretation is complicated by high placebo response rates and selective publication of clinical trial results.
Maintenance therapy
The majority of patients treated with an antipsychotic drug will experience a response within four weeks. The goals of continuing treatment are to maintain suppression of symptoms, prevent relapse, improve quality of life, and support engagement in psychosocial therapy.
Maintenance therapy with antipsychotic drugs is clearly superior to placebo in preventing relapse but is associated with weight gain, movement disorders, and high dropout rates. A 3-year trial following persons receiving maintenance therapy after an acute psychotic episode found that 33% obtained long-lasting symptom reduction, 13% achieved remission, and only 27% experienced satisfactory quality of life. The effect of relapse prevention on long term outcomes is uncertain, as historical studies show little difference in long term outcomes before and after the introduction of antipsychotic drugs.
While maintenance therapy clearly reduces the rate of relapses requiring hospitalization, a large observational study in Finland found that, in people that eventually discontinued antipsychotics, the risk of being hospitalized again for a mental health problem or dying increased the longer they were dispensed (and presumably took) antipsychotics prior to stopping therapy. If people did not stop taking antipsychotics, they remained at low risk for relapse and hospitalization compared to those that did. The authors speculated that the difference may be because the people that discontinued treatment after a longer time had more severe mental illness than those that discontinued antipsychotic therapy sooner. | Antipsychotic | Wikipedia | 453 | 2870 | https://en.wikipedia.org/wiki/Antipsychotic | Biology and health sciences | Psychiatric drugs | Health |
A significant challenge in the use of antipsychotic drugs for the prevention of relapse is the poor rate of adherence. In spite of the relatively high rates of adverse effects associated with these drugs, some evidence, including higher dropout rates in placebo arms compared to treatment arms in randomized clinical trials, suggests that most patients who discontinue treatment do so because of suboptimal efficacy. If someone experiences psychotic symptoms due to nonadherence, they may be compelled to receive treatment through a process called involuntary commitment, in which they can be forced to accept treatment (including antipsychotics). A person can also be committed to treatment outside of a hospital, called outpatient commitment.
Antipsychotics in long-acting injectable (LAI), or "depot", form have been suggested as a method of decreasing medication nonadherence (sometimes also called non-compliance). NICE advises LAIs be offered to patients when preventing covert, intentional nonadherence is a clinical priority. LAIs are used to ensure adherence in outpatient commitment. A meta-analysis found that LAIs resulted in lower rates of rehospitalization with a hazard ratio of 0.83; however, these results were not statistically significant (the 95% confidence interval was 0.62 to 1.11).
Bipolar disorder
Antipsychotics are routinely used, often in conjunction with mood stabilizers such as lithium/valproate, as a first-line treatment for manic and mixed episodes associated with bipolar disorder. The reason for this combination is the therapeutic delay of the aforementioned mood stabilizers (for valproate therapeutic effects are usually seen around five days after treatment is commenced whereas lithium usually takes at least a week before the full therapeutic effects are seen) and the comparatively rapid antimanic effects of antipsychotic drugs. The antipsychotics have a documented efficacy when used alone in acute mania/mixed episodes. | Antipsychotic | Wikipedia | 397 | 2870 | https://en.wikipedia.org/wiki/Antipsychotic | Biology and health sciences | Psychiatric drugs | Health |
At least five atypical antipsychotics (lumateperone, cariprazine, lurasidone, olanzapine, and quetiapine) have also been found to possess efficacy in the treatment of bipolar depression as a monotherapy, whereas only olanzapine and quetiapine have been proven to be effective broad-spectrum (i.e., against all three types of relapse—manic, mixed and depressive) prophylactic (or maintenance) treatments in patients with bipolar disorder. A recent Cochrane review also found that olanzapine had a less favourable risk/benefit ratio than lithium as a maintenance treatment for bipolar disorder.
The American Psychiatric Association and the UK National Institute for Health and Care Excellence recommend antipsychotics for managing acute psychotic episodes in schizophrenia or bipolar disorder, and as a longer-term maintenance treatment for reducing the likelihood of further episodes. They state that response to any given antipsychotic can be variable so that trials may be necessary, and that lower doses are to be preferred where possible. A number of studies have looked at levels of "compliance" or "adherence" with antipsychotic regimes and found that discontinuation (stopping taking them) by patients is associated with higher rates of relapse, including hospitalization.
Dementia
Psychosis and agitation develop in as many as 80 percent of people living in nursing homes. Despite a lack of FDA approval and black-box warnings, atypical antipsychotics are very often prescribed to people with dementia. An assessment for an underlying cause of behavior is needed before prescribing antipsychotic medication for symptoms of dementia. Antipsychotics in old age dementia showed a modest benefit compared to placebo in managing aggression or psychosis, but this is combined with a fairly large increase in serious adverse events. Thus, antipsychotics should not be used routinely to treat dementia with aggression or psychosis, but may be an option in a few cases where there is severe distress or risk of physical harm to others. Psychosocial interventions may reduce the need for antipsychotics. In 2005, the FDA issued an advisory warning of an increased risk of death when atypical antipsychotics are used in dementia. In the subsequent 5 years, the use of atypical antipsychotics to treat dementia decreased by nearly 50%. | Antipsychotic | Wikipedia | 482 | 2870 | https://en.wikipedia.org/wiki/Antipsychotic | Biology and health sciences | Psychiatric drugs | Health |
Major depressive disorder
A number of atypical antipsychotics have some benefits when used in addition to other treatments in major depressive disorder. Aripiprazole, quetiapine extended-release, and olanzapine (when used in conjunction with fluoxetine) have received the Food and Drug Administration (FDA) labelling for this indication. There is, however, a greater risk of side effects with their use compared to using traditional antidepressants. The greater risk of serious side effects with antipsychotics is why, e.g., quetiapine was denied approval as monotherapy for major depressive disorder or generalized anxiety disorder, and instead was only approved as an adjunctive treatment in combination with traditional antidepressants.
A recent study on the use of antipychotics in unipolar depression concluded that the use of those drugs in addition to antidepressants alone leads to a worse disease outcome. This effect is especially pronounced in younger patients with psychotic unipolar depression. Considering the wide use of such combination therapies, further studies on the side effects of antipychotics as an add-on therapy are warranted. | Antipsychotic | Wikipedia | 240 | 2870 | https://en.wikipedia.org/wiki/Antipsychotic | Biology and health sciences | Psychiatric drugs | Health |
Other
Global antipsychotic utilization has seen a steady growth since the introduction of atypical (second-generation) antipsychotics and this is ascribed to off-label use for many other unapproved disorders. Besides the above uses antipsychotics may be used for obsessive–compulsive disorder, post-traumatic stress disorder, personality disorders, Tourette syndrome, autism and agitation in those with dementia. Evidence however does not support the use of atypical antipsychotics in eating disorders or personality disorder. The atypical antipsychotic risperidone may be useful for obsessive–compulsive disorder. The use of low doses of antipsychotics for insomnia, while common, is not recommended as there is little evidence of benefit as well as concern regarding adverse effects. Some of the more serious adverse effects may also occur at the low doses used, such as dyslipidemia and neutropenia, and a recent network meta-analysis of 154 double-blind, randomized controlled trials of drug therapies vs. placebo for insomnia in adults found that quetiapine did not demonstrated any short-term benefits in sleep quality. Low dose antipsychotics may also be used in treatment of impulse-behavioural and cognitive-perceptual symptoms of borderline personality disorder. Despite the lack of evidence supporting the benefit of antipsychotics in people with personality disorders, 1 in 4 who do not have a serious mental illness are prescribed them in UK primary care. Many people receive these medication for over a year, contrary to NICE guidelines. | Antipsychotic | Wikipedia | 334 | 2870 | https://en.wikipedia.org/wiki/Antipsychotic | Biology and health sciences | Psychiatric drugs | Health |
In children they may be used in those with disruptive behavior disorders, mood disorders and pervasive developmental disorders or intellectual disability. Antipsychotics are only weakly recommended for Tourette syndrome, because although they are effective, side effects are common. The situation is similar for those on the autism spectrum.
Much of the evidence for the off-label use of antipsychotics (for example, for dementia, OCD, PTSD, personality disorders, Tourette's) was of insufficient scientific quality to support such use, especially as there was strong evidence of increased risks of stroke, tremors, significant weight gain, sedation, and gastrointestinal problems. A UK review of unlicensed usage in children and adolescents reported a similar mixture of findings and concerns. A survey of children with pervasive developmental disorder found that 16.5% were taking an antipsychotic drug, most commonly for irritability, aggression, and agitation. Both risperidone and aripiprazole have been approved by the US FDA for the treatment of irritability in autistic children and adolescents. A review in the UK found that the use of antipsychotics in England doubled between 2000 and 2019. Children were prescribed antipsychotics for conditions for which there is no approval, such as autism.
Aggressive challenging behavior in adults with intellectual disability is often treated with antipsychotic drugs despite lack of an evidence base. A recent randomized controlled trial, however, found no benefit over placebo and recommended that the use of antipsychotics in this way should no longer be regarded as an acceptable routine treatment.
Antipsychotics may be an option, together with stimulants, in people with ADHD and aggressive behavior when other treatments have not worked. They have not been found to be useful for the prevention of delirium among those admitted to hospital.
Typicals vs atypicals
Aside from reduced extrapyramidal symptoms, and with the clear exception of clozapine, it is unclear whether the atypical (second-generation) antipsychotics offer advantages over older, first generation antipsychotics. Amisulpride, olanzapine, risperidone and clozapine may be more effective but are associated with greater side effects. Typical antipsychotics have equal drop-out and symptom relapse rates to atypicals when used at low to moderate dosages. | Antipsychotic | Wikipedia | 500 | 2870 | https://en.wikipedia.org/wiki/Antipsychotic | Biology and health sciences | Psychiatric drugs | Health |
Clozapine is an effective treatment for those who respond poorly to other drugs ("treatment-resistant" or "refractory" schizophrenia), but it has the potentially serious side effect of agranulocytosis (lowered white blood cell count) in less than 4% of people.
Due to bias in the research the accuracy of comparisons of atypical antipsychotics is a concern.
In 2005, a US government body, the National Institute of Mental Health published the results of a major independent study (the CATIE project). No other atypical studied (risperidone, quetiapine, and ziprasidone) did better than the first-generation antipsychotic perphenazine on the measures used, nor did they produce fewer adverse effects than the typical antipsychotic perphenazine, although more patients discontinued perphenazine owing to extrapyramidal effects compared to the atypical agents (8% vs. 2% to 4%). This is significant because any patient with tardive dyskinesia was specifically excluded from randomization to perphenazine; i.e., in the CATIE study the patient cohort randomized to receive perphenazne was at lower risk of having extrapyramidal symptoms.
Atypical antipsychotics do not appear to lead to improved rates of medication adherence compared to typical antipsychotics.
Many researchers question the first-line prescribing of atypicals over typicals, and some even question the distinction between the two classes. In contrast, other researchers point to the significantly higher risk of tardive dyskinesia and other extrapyramidal symptoms with the typicals and for this reason alone recommend first-line treatment with the atypicals, notwithstanding a greater propensity for metabolic adverse effects in the latter. The UK government organization NICE recently revised its recommendation favoring atypicals, to advise that the choice should be an individual one based on the particular profiles of the individual drug and on the patient's preferences.
The re-evaluation of the evidence has not necessarily slowed the bias toward prescribing the atypicals. | Antipsychotic | Wikipedia | 453 | 2870 | https://en.wikipedia.org/wiki/Antipsychotic | Biology and health sciences | Psychiatric drugs | Health |
Other uses
Antipsychotics, such as risperidone, quetiapine, and olanzapine, have been used as hallucinogen antidotes or "trip killers" to block the effects of serotonergic psychedelics like psilocybin and lysergic acid diethylamide (LSD).
Adverse effects
Generally, more than one antipsychotic drug should not be used at a time because of increased adverse effects.
Some atypicals are associated with considerable weight gain, diabetes and the risk of metabolic syndrome. Unwanted side effects cause people to stop treatment, resulting in relapses. Risperidone (atypical) has a similar rate of extrapyramidal symptoms to haloperidol (typical). A rare but potentially lethal condition of neuroleptic malignant syndrome (NMS) has been associated with the use of antipsychotics. Through its early recognition, and timely intervention rates have declined. However, an awareness of the syndrome is advised to enable intervention. Another less rare condition of tardive dyskinesia can occur due to long-term use of antipsychotics, developing after months or years of use. It is more often reported with use of typical antipsychotics. Very rarely antipsychotics may cause tardive psychosis.
Clozapine is associated with side effects that include weight gain, tiredness, and hypersalivation. More serious adverse effects include seizures, NMS, neutropenia, and agranulocytosis (lowered white blood cell count) and its use needs careful monitoring. | Antipsychotic | Wikipedia | 333 | 2870 | https://en.wikipedia.org/wiki/Antipsychotic | Biology and health sciences | Psychiatric drugs | Health |
Clozapine is also associated with thromboembolism (including pulmonary embolism), myocarditis, and cardiomyopathy. A systematic review of clozapine-associated pulmonary embolism indicates that this adverse effect can often be fatal, and that it has an early onset, and is dose-dependent. The findings advised the consideration of using a prevention therapy for venous thromboembolism after starting treatment with clozapine, and continuing this for six months. Constipation is three times more likely to occur with the use of clozapine, and severe cases can lead to ileus and bowel ischemia resulting in many fatalities. Very rare clozapine adverse effects include periorbital edema due to several possible mechanisms (e.g., inhibition of platelet-derived growth factor receptors leading to increased vascular permeability, antagonism of renal dopamine receptors with electrolyte and fluid imbalance and immune-mediated hypersensitivity reactions).
However, the risk of serious adverse effects from clozapine is low, and there are the beneficial effects to be gained of a reduced risk of suicide, and aggression. Typical antipsychotics and atypical risperidone can have a side effect of sexual dysfunction. Clozapine, olanzapine, and quetiapine are associated with beneficial effects on sexual functioning helped by various psychotherapies. | Antipsychotic | Wikipedia | 295 | 2870 | https://en.wikipedia.org/wiki/Antipsychotic | Biology and health sciences | Psychiatric drugs | Health |
By rate
Common (≥ 1% and up to 50% incidence for most antipsychotic drugs) adverse effects of antipsychotics include:
Dysphoria and apathy (due to dopamine receptor blockade)
Sedation (particularly common with asenapine, clozapine, olanzapine, quetiapine, chlorpromazine and zotepine)
Headaches
Dizziness
Diarrhea
Anxiety
Extrapyramidal side effects (particularly common with first-generation antipsychotics), which include:
Akathisia, an often distressing sense of inner restlessness.
Dystonia, an abnormal muscle contraction
Pseudoparkinsonism, symptoms that are similar to what people with Parkinson's disease experience, including tremulousness and drooling
Hyperprolactinaemia (rare for those treated with clozapine, quetiapine and aripiprazole), which can cause:
Galactorrhoea, the unusual secretion of breast milk.
Gynaecomastia, abnormal growth of breast tissue
Sexual dysfunction (in both sexes)
Osteoporosis
Orthostatic hypotension
Weight gain (particularly prominent with clozapine, olanzapine, quetiapine and zotepine, can be counteracted by starting the drug with metformin)
Anticholinergic side-effects (common for olanzapine, clozapine; less likely on risperidone) such as:
Blurred vision
Constipation
Dry mouth (although hypersalivation may also occur)
Reduced perspiration
Tardive dyskinesia appears to be more frequent with high-potency first-generation antipsychotics, such as haloperidol, and tends to appear after chronic and not acute treatment. It is characterized by slow (hence the tardive) repetitive, involuntary and purposeless movements, most often of the face, lips, legs, or torso, which tend to resist treatment and are frequently irreversible. The rate of appearance of TD is about 5% per year of use of antipsychotic drug (whatever the drug used)
Breast cancer: a systematic review and meta-analysis of observational studies with over 2 million individuals estimated an association between antipsychotic use and breast cancer by over 30%. | Antipsychotic | Wikipedia | 476 | 2870 | https://en.wikipedia.org/wiki/Antipsychotic | Biology and health sciences | Psychiatric drugs | Health |
Rare/Uncommon (<1% incidence for most antipsychotic drugs) adverse effects of antipsychotics include:
Blood dyscrasias (e.g., agranulocytosis, leukopenia, and neutropaenia), which is more common in patients on clozapine.
Metabolic syndrome and other metabolic problems such as type II diabetes mellitus — particularly common with clozapine, olanzapine and zotepine. In American studies African Americans appeared to be at a heightened risk for developing type II diabetes mellitus. Evidence suggests that females are more sensitive to the metabolic side effects of first-generation antipsychotic drugs than males. Metabolic adverse effects appear to be mediated by antagonizing the histamine H1 and serotonin 5-HT2C receptors and perhaps by interacting with other neurochemical pathways in the central nervous system.
Neuroleptic malignant syndrome, a potentially fatal condition characterized by:
Autonomic instability, which can manifest with tachycardia, nausea, vomiting, diaphoresis, etc.
Hyperthermia — elevated body temperature.
Mental status change (confusion, hallucinations, coma, etc.)
Muscle rigidity
Laboratory abnormalities (e.g., elevated creatine kinase, reduced iron plasma levels, electrolyte abnormalities, etc.)
Pancreatitis
QT interval prolongation — more prominent in those treated with amisulpride, pimozide, sertindole, thioridazine and ziprasidone.
Torsades de pointes
Seizures, particularly in people treated with chlorpromazine and clozapine.
Thromboembolism
Myocardial infarction
Stroke
Pisa syndrome
Long-term effects | Antipsychotic | Wikipedia | 364 | 2870 | https://en.wikipedia.org/wiki/Antipsychotic | Biology and health sciences | Psychiatric drugs | Health |
Some studies have found decreased life expectancy associated with the use of antipsychotics, and argued that more studies are needed. Antipsychotics may also increase the risk of early death in individuals with dementia. Antipsychotics typically worsen symptoms in people with depersonalisation disorder. Antipsychotic polypharmacy (prescribing two or more antipsychotics at the same time for an individual) is a common practice but not evidence-based or recommended, and there are initiatives to curtail it. Similarly, the use of excessively high doses (often the result of polypharmacy) continues despite clinical guidelines and evidence indicating that it is usually no more effective but is usually more harmful. A meta-analysis of observational studies with over two million individuals has suggested a moderate association of antipsychotic use with breast cancer.
Loss of grey matter and other brain structural changes over time are observed amongst people diagnosed with schizophrenia. Meta-analyses of the effects of antipsychotic treatment on grey matter volume and the brain's structure have reached conflicting conclusions. A 2012 meta-analysis concluded that grey matter loss is greater in patients treated with first generation antipsychotics relative to those treated with atypicals, and hypothesized a protective effect of atypicals as one possible explanation. A second meta-analysis suggested that treatment with antipsychotics was associated with increased grey matter loss. Animal studies found that monkeys exposed to both first- and second-generation antipsychotics experience significant reduction in brain volume, resulting in an 8-11% reduction in brain volume over a 17–27 month period.
The National Association of State Mental Health Program Directors said that antipsychotics are not interchangeable, and it recommends including trying at least one weight-neutral treatment for those patients with potential metabolic issues.
Subtle, long-lasting forms of akathisia are often overlooked or confused with post-psychotic depression, in particular when they lack the extrapyramidal aspect that psychiatrists have been taught to expect when looking for signs of akathisia.
Adverse effect on cognitive function and increased risk of death in people with dementia along with worsening of symptoms has been described in the literature. | Antipsychotic | Wikipedia | 453 | 2870 | https://en.wikipedia.org/wiki/Antipsychotic | Biology and health sciences | Psychiatric drugs | Health |
Antipsychotics, due to acting as dopamine D2 receptor antagonists and thereby stimulating pituitary lactotrophs, may have a risk of prolactinoma with long-term use. This is also responsible for their induction of hyperprolactinemia (high prolactin levels).
Discontinuation
The British National Formulary recommends a gradual withdrawal when discontinuing antipsychotics to avoid acute withdrawal syndrome or rapid relapse. Symptoms of withdrawal commonly include nausea, vomiting, and loss of appetite. Other symptoms may include restlessness, increased sweating, and trouble sleeping. Less commonly there may be a feeling of the world spinning, numbness, or muscle pains. Symptoms generally resolve after a short period of time.
There is tentative evidence that discontinuation of antipsychotics can result in psychosis. It may also result in recurrence of the condition that is being treated. Rarely, tardive dyskinesia can occur when the medication is stopped.
Unexpected psychotic episodes have been observed in patients withdrawing from clozapine. This is referred to as supersensitivity psychosis, not to be equated with tardive dyskinesia.
Tardive dyskinesia may abate during withdrawal from the antipsychotic agent, or it may persist.
Withdrawal effects may also occur when switching a person from one antipsychotic to another, (it is presumed due to variations of potency and receptor activity). Such withdrawal effects can include cholinergic rebound, an activation syndrome, and motor syndromes including dyskinesias. These adverse effects are more likely during rapid changes between antipsychotic agents, so making a gradual change between antipsychotics minimises these withdrawal effects. The British National Formulary recommends a gradual dose reduction when discontinuing antipsychotic treatment to avoid acute withdrawal symptoms or rapid relapse. The process of cross-titration involves gradually increasing the dose of the new medication while gradually decreasing the dose of the old medication.
City and Hackney Clinical Commissioning Group found more than 1,000 patients in their area in July 2019 who had not had regular medication reviews or health checks because they were not registered as having serious mental illness. On average they had been taking these drugs for six years. If this is typical of practice in England more than 100,000 patients are probably in the same position.
List of agents | Antipsychotic | Wikipedia | 504 | 2870 | https://en.wikipedia.org/wiki/Antipsychotic | Biology and health sciences | Psychiatric drugs | Health |
Clinically used antipsychotic medications are listed below by drug group. Trade names appear in parentheses. A 2013 review has stated that the division of antipsychotics into first and second generation is perhaps not accurate. | Antipsychotic | Wikipedia | 44 | 2870 | https://en.wikipedia.org/wiki/Antipsychotic | Biology and health sciences | Psychiatric drugs | Health |
Amoxicillin is an antibiotic medication belonging to the aminopenicillin class of the penicillin family. The drug is used to treat bacterial infections such as middle ear infection, strep throat, pneumonia, skin infections, odontogenic infections, and urinary tract infections. It is taken orally (swallowed by mouth), or less commonly by either intramuscular injection or by an IV bolus injection, which is a relatively quick intravenous injection lasting from a couple of seconds to a few minutes.
Common adverse effects include nausea and rash. It may also increase the risk of yeast infections and, when used in combination with clavulanic acid, diarrhea. It should not be used in those who are allergic to penicillin. While usable in those with kidney problems, the dose may need to be decreased. Its use in pregnancy and breastfeeding does not appear to be harmful. Amoxicillin is in the β-lactam family of antibiotics.
Amoxicillin was discovered in 1958 and came into medical use in 1972. Amoxil was approved for medical use in the United States in 1974, and in the United Kingdom in 1977. It is on the World Health Organization's List of Essential Medicines. It is one of the most commonly prescribed antibiotics in children. Amoxicillin is available as a generic medication. In 2022, it was the 26th most commonly prescribed medication in the United States, with more than 20million prescriptions.
Medical uses
Amoxicillin is used in the treatment of a number of infections, including acute otitis media, streptococcal pharyngitis, pneumonia, skin infections, urinary tract infections, Salmonella infections, Lyme disease, and chlamydia infections.
Acute otitis media
Children with acute otitis media who are younger than six months of age are generally treated with amoxicillin or other antibiotics. Although most children with acute otitis media who are older than two years old do not benefit from treatment with amoxicillin or other antibiotics, such treatment may be helpful in children younger than two years old with acute otitis media that is bilateral or accompanied by ear drainage. In the past, amoxicillin was dosed three times daily when used to treat acute otitis media, which resulted in missed doses in routine ambulatory practice. There is now evidence that two-times daily dosing or once-daily dosing has similar effectiveness. | Amoxicillin | Wikipedia | 507 | 2885 | https://en.wikipedia.org/wiki/Amoxicillin | Biology and health sciences | Antibiotics | Health |
Respiratory infections
Most sinusitis infections are caused by viruses, for which amoxicillin and amoxicillin-clavulanate are ineffective, and the small benefit gained by amoxicillin may be overridden by the adverse effects.
Amoxicillin is considered the first-line empirical treatment for most cases of uncomplicated bacterial sinusitis in children and adults when culture data is unavailable. Amoxicillin is recommended as the preferred first-line treatment for community-acquired pneumonia in adults by the National Institute for Health and Care Excellence, either alone (mild to moderate severity disease) or in combination with a macrolide. Research suggests that is as effective as co-amoxiclav (a broad-spectrum antibiotic) for people admitted to hospital with pneumonia, regardless of its severity. The World Health Organization (WHO) recommends amoxicillin as first-line treatment for pneumonia that is not "severe". Amoxicillin is used in post-exposure inhalation of anthrax to prevent disease progression and for prophylaxis.
H. pylori
It is effective as one part of a multi-drug regimen for the treatment of stomach infections of Helicobacter pylori. It is typically combined with a proton-pump inhibitor (such as omeprazole) and a macrolide antibiotic (such as clarithromycin); other drug combinations are also effective.
Lyme borreliosis
Amoxicillin is effective for the treatment of early cutaneous Lyme borreliosis; the effectiveness and safety of oral amoxicillin is neither better nor worse than common alternatively-used antibiotics.
Odontogenic infections
Amoxicillin is used to treat odontogenic infections, infections of the tongue, lips, and other oral tissues. It may be prescribed following a tooth extraction, particularly in those with compromised immune systems.
Skin infections
Amoxicillin is occasionally used for the treatment of skin infections, such as acne vulgaris. It is often an effective treatment for cases of acne vulgaris that have responded poorly to other antibiotics, such as doxycycline and minocycline. | Amoxicillin | Wikipedia | 450 | 2885 | https://en.wikipedia.org/wiki/Amoxicillin | Biology and health sciences | Antibiotics | Health |
Infections in infants in resource-limited settings
Amoxicillin is recommended by the World Health Organization for the treatment of infants with signs and symptoms of pneumonia in resource-limited situations when the parents are unable or unwilling to accept hospitalization of the child. Amoxicillin in combination with gentamicin is recommended for the treatment of infants with signs of other severe infections when hospitalization is not an option.
Prevention of bacterial endocarditis
It is also used to prevent bacterial endocarditis and as a pain-reliever in high-risk people having dental work done, to prevent Streptococcus pneumoniae and other encapsulated bacterial infections in those without spleens, such as people with sickle-cell disease, and for both the prevention and the treatment of anthrax. The United Kingdom recommends against its use for infectious endocarditis prophylaxis. These recommendations do not appear to have changed the rates of infection for infectious endocarditis.
Combination treatment
Amoxicillin is susceptible to degradation by β-lactamase-producing bacteria, which are resistant to most β-lactam antibiotics, such as penicillin. For this reason, it may be combined with clavulanic acid, a β-lactamase inhibitor. This drug combination is commonly called co-amoxiclav.
Spectrum of activity
It is a moderate-spectrum, bacteriolytic, β-lactam antibiotic in the aminopenicillin family used to treat susceptible Gram-positive and Gram-negative bacteria. It is usually the drug of choice within the class because it is better absorbed, following oral administration, than other β-lactam antibiotics.
In general, Streptococcus, Bacillus subtilis, Enterococcus, Haemophilus, Helicobacter, and Moraxella are susceptible to amoxicillin, whereas Citrobacter, Klebsiella and Pseudomonas aeruginosa are resistant to it. Some E. coli and most clinical strains of Staphylococcus aureus have developed resistance to amoxicillin to varying degrees.
Adverse effects
Adverse effects are similar to those for other β-lactam antibiotics, including nausea, vomiting, rashes, and antibiotic-associated colitis. Diarrhea (loose bowel movements) may also occur. | Amoxicillin | Wikipedia | 484 | 2885 | https://en.wikipedia.org/wiki/Amoxicillin | Biology and health sciences | Antibiotics | Health |
Rarer adverse effects include mental and behavioral changes, lightheadedness, insomnia, hyperactivity, agitation, confusion, anxiety, sensitivity to lights and sounds, and unclear thinking. Immediate medical care is required upon the first signs of these adverse effects. Similarly to other penicillins, amoxicillin has been associated with an increased risk of seizures. Amoxicillin-induced neurotoxicity has been especially associated with concentrations of greater than 110mg/L.
The onset of an allergic reaction to amoxicillin can be very sudden and intense; emergency medical attention must be sought as quickly as possible. The initial phase of such a reaction often starts with a change in mental state, skin rash with intense itching (often beginning in the fingertips and around the groin area and rapidly spreading), and sensations of fever, nausea, and vomiting. Any other symptoms that seem even remotely suspicious must be taken very seriously. However, more mild allergy symptoms, such as a rash, can occur at any time during treatment, even up to a week after treatment has ceased. For some people allergic to amoxicillin, the adverse effects can be fatal due to anaphylaxis.
Use of the amoxicillin/clavulanic acid combination for more than one week has caused a drug-induced immunoallergic-type hepatitis in some patients. Young children having ingested acute overdoses of amoxicillin manifested lethargy, vomiting, and renal dysfunction.
There is poor reporting of adverse effects of amoxicillin from clinical trials. For this reason, the severity and frequency of adverse effects from amoxicillin are probably higher than reported in clinical trials.
Nonallergic rash
Between 3 and 10% of children taking amoxicillin (or ampicillin) show a late-developing (>72 hours after beginning medication and having never taken penicillin-like medication previously) rash, which is sometimes referred to as the "amoxicillin rash". The rash can also occur in adults and may rarely be a component of the DRESS syndrome. | Amoxicillin | Wikipedia | 429 | 2885 | https://en.wikipedia.org/wiki/Amoxicillin | Biology and health sciences | Antibiotics | Health |
The rash is described as maculopapular or morbilliform (measles-like; therefore, in medical literature, it is called "amoxicillin-induced morbilliform rash".). It starts on the trunk and can spread from there. This rash is unlikely to be a true allergic reaction and is not a contraindication for future amoxicillin usage, nor should the current regimen necessarily be stopped. However, this common amoxicillin rash and a dangerous allergic reaction cannot easily be distinguished by inexperienced persons, so a healthcare professional is often required to distinguish between the two.
A nonallergic amoxicillin rash may also be an indicator of infectious mononucleosis. Some studies indicate about 80–90% of patients with acute Epstein–Barr virus infection treated with amoxicillin or ampicillin develop such a rash.
Interactions
Amoxicillin may interact with these drugs:
Anticoagulants (dabigatran, warfarin).
Methotrexate (chemotherapy and immunosuppressant).
Typhoid, Cholera and BCG vaccines.
Probenecid reduces renal excretion and increases blood levels of amoxicillin.
Oral contraceptives potentially become less effective.
Allopurinol (gout treatment).
Mycophenolate (immunosuppressant)
When given intravenously or intramuscularly:
It should not be mixed with blood products, or proteinaceous fluids (including protein hydrolysates) or with intravenous lipid emulsions
aminoglycoside should be injected at a separate site from amoxicillin if the patient is prescribed both medications at the same time. Neither drug should be mixed in a syringe. Neither should they be mixed in an intravenous fluid container or giving set because of loss of activity of the aminoglycoside under these conditions.
ciprofloxacin should not be mixed with amoxicillin.
Infusions containing dextran or bicarbonate should not be mixed with amoxicillin solutions. | Amoxicillin | Wikipedia | 434 | 2885 | https://en.wikipedia.org/wiki/Amoxicillin | Biology and health sciences | Antibiotics | Health |
Pharmacology
Amoxicillin (α-amino-p-hydroxybenzyl penicillin) is a semisynthetic derivative of penicillin with a structure similar to ampicillin but with better absorption when taken by mouth, thus yielding higher concentrations in blood and in urine. Amoxicillin diffuses easily into tissues and body fluids. It will cross the placenta and is excreted into breastmilk in small quantities. It is metabolized by the liver and excreted into the urine. It has an onset of 30 minutes and a half-life of 3.7 hours in newborns and 1.4 hours in adults.
Amoxicillin attaches to the cell wall of susceptible bacteria and results in their death. It is effective against streptococci, pneumococci, enterococci, Haemophilus influenzae, Escherichia coli, Proteus mirabilis, Neisseria meningitidis, Neisseria gonorrhoeae, Shigella, Chlamydia trachomatis, Salmonella, Borrelia burgdorferi, and Helicobacter pylori. As a derivative of ampicillin, amoxicillin is a member of the penicillin family and, like penicillins, is a β-lactam antibiotic. It inhibits cross-linkage between the linear peptidoglycan polymer chains that make up a major component of the bacterial cell wall. It has two ionizable groups in the physiological range (the amino group in alpha-position to the amide carbonyl group and the carboxyl group).
Chemistry
Amoxicillin is a β-lactam and aminopenicillin antibiotic in terms of chemical structure. It is structurally related to ampicillin.
The experimental log P of amoxicillin is 0.87. It is described as an "ambiphilic"—between hydrophilic and lipophilic—antibiotic.
History | Amoxicillin | Wikipedia | 421 | 2885 | https://en.wikipedia.org/wiki/Amoxicillin | Biology and health sciences | Antibiotics | Health |
Amoxicillin was one of several semisynthetic derivatives of 6-aminopenicillanic acid (6-APA) developed by the Beecham Group in the 1960s. It was invented by Anthony Alfred Walter Long and John Herbert Charles Nayler, two British scientists. It became available in 1972 and was the second aminopenicillin to reach the market (after ampicillin in 1961). Co-amoxiclav became available in 1981.
Society and culture
Economics
Amoxicillin is relatively inexpensive. In 2022, a survey of eight generic antibiotics commonly prescribed in the United States found their average cost to be about $42.67, while amoxicillin was sold for $12.14 on average.
Modes of delivery
Pharmaceutical manufacturers make amoxicillin in trihydrate form, for oral use available as capsules, regular, chewable and dispersible tablets, syrup and pediatric suspension for oral use, and as the sodium salt for intravenous administration.
An extended-release is available. The intravenous form of amoxicillin is not sold in the United States. When an intravenous aminopenicillin is required in the United States, ampicillin is typically used. When there is an adequate response to ampicillin, the course of antibiotic therapy may often be completed with oral amoxicillin.
Research with mice indicated successful delivery using intraperitoneally injected amoxicillin-bearing microparticles.
Names
Amoxicillin is the international nonproprietary name (INN), British Approved Name (BAN), and United States Adopted Name (USAN), while amoxycillin is the Australian Approved Name (AAN).
Amoxicillin is one of the semisynthetic penicillins discovered by the former pharmaceutical company Beecham Group. The patent for amoxicillin has expired, thus amoxicillin and co-amoxiclav preparations are marketed under various brand names across the world.
Veterinary uses
Amoxicillin is also sometimes used as an antibiotic for animals. The use of amoxicillin for animals intended for human consumption (chickens, cattle, and swine for example) has been approved. | Amoxicillin | Wikipedia | 457 | 2885 | https://en.wikipedia.org/wiki/Amoxicillin | Biology and health sciences | Antibiotics | Health |
In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid) is a solid that lacks the long-range order that is characteristic of a crystal. The terms "glass" and "glassy solid" are sometimes used synonymously with amorphous solid; however, these terms refer specifically to amorphous materials that undergo a glass transition. Examples of amorphous solids include glasses, metallic glasses, and certain types of plastics and polymers.
Etymology
The term comes from the Greek a ("without"), and morphé ("shape, form").
Structure
Amorphous materials have an internal structure of molecular-scale structural blocks that can be similar to the basic structural units in the crystalline phase of the same compound. Unlike in crystalline materials, however, no long-range regularity exists: amorphous materials cannot be described by the repetition of a finite unit cell. Statistical measures, such as the atomic density function and radial distribution function, are more useful in describing the structure of amorphous solids.
Although amorphous materials lack long range order, they exhibit localized order on small length scales. By convention, short range order extends only to the nearest neighbor shell, typically only 1-2 atomic spacings. Medium range order may extend beyond the short range order by 1-2 nm.
Fundamental properties of amorphous solids
Glass transition at high temperatures
The freezing from liquid state to amorphous solid - glass transition - is considered one of the very important and unsolved problems of physics.
Universal low-temperature properties of amorphous solids
At very low temperatures (below 1-10 K), a large family of amorphous solids have various similar low-temperature properties.
Although there are various theoretical models, neither glass transition nor low-temperature properties of glassy solids are well understood on the fundamental physics level.
Amorphous solids is an important area of condensed matter physics aiming to understand these substances at high temperatures of glass transition and at low temperatures towards absolute zero. From the 1970s, low-temperature properties of amorphous solids were studied experimentally in great detail. For all of these substances, specific heat has a (nearly) linear dependence as a function of temperature, and thermal conductivity has nearly quadratic temperature dependence. These properties are conventionally called anomalous being very different from properties of crystalline solids. | Amorphous solid | Wikipedia | 481 | 2889 | https://en.wikipedia.org/wiki/Amorphous%20solid | Physical sciences | Basics_8 | null |
On the phenomenological level, many of these properties were described by a collection of tunnelling two-level systems. Nevertheless, the microscopic theory of these properties is still missing after more than 50 years of the research.
Remarkably, a dimensionless quantity of internal friction is nearly universal in these materials. This quantity is a dimensionless ratio (up to a numerical constant) of the phonon wavelength to the phonon mean free path. Since the theory of tunnelling two-level states (TLSs) does not address the origin of the density of TLSs, this theory cannot explain the universality of internal friction, which in turn is proportional to the density of scattering TLSs. The theoretical significance of this important and unsolved problem was highlighted by Anthony Leggett.
Nano-structured materials
Amorphous materials will have some degree of short-range order at the atomic-length scale due to the nature of intermolecular chemical bonding. Furthermore, in very small crystals, short-range order encompasses a large fraction of the atoms; nevertheless, relaxation at the surface, along with interfacial effects, distorts the atomic positions and decreases structural order. Even the most advanced structural characterization techniques, such as X-ray diffraction and transmission electron microscopy, can have difficulty distinguishing amorphous and crystalline structures at short-size scales.
Characterization of amorphous solids
Due to the lack of long-range order, standard crystallographic techniques are often inadequate in determining the structure of amorphous solids. A variety of electron, X-ray, and computation-based techniques have been used to characterize amorphous materials. Multi-modal analysis is very common for amorphous materials. | Amorphous solid | Wikipedia | 351 | 2889 | https://en.wikipedia.org/wiki/Amorphous%20solid | Physical sciences | Basics_8 | null |
X-ray and neutron diffraction
Unlike crystalline materials, which exhibit strong Bragg diffraction, the diffraction patterns of amorphous materials are characterized by broad and diffuse peaks. As a result, detailed analysis and complementary techniques are required to extract real space structural information from the diffraction patterns of amorphous materials. It is useful to obtain diffraction data from both X-ray and neutron sources as they have different scattering properties and provide complementary data. Pair distribution function analysis can be performed on diffraction data to determine the probability of finding a pair of atoms separated by a certain distance. Another type of analysis that is done with diffraction data of amorphous materials is radial distribution function analysis, which measures the number of atoms found at varying radial distances away from an arbitrary reference atom. From these techniques, the local order of an amorphous material can be elucidated.
X-ray absorption fine-structure spectroscopy
X-ray absorption fine-structure spectroscopy is an atomic scale probe making it useful for studying materials lacking in long-range order. Spectra obtained using this method provide information on the oxidation state, coordination number, and species surrounding the atom in question as well as the distances at which they are found.
Atomic electron tomography
The atomic electron tomography technique is performed in transmission electron microscopes capable of reaching sub-Angstrom resolution. A collection of 2D images taken at numerous different tilt angles is acquired from the sample in question and then used to reconstruct a 3D image. After image acquisition, a significant amount of processing must be done to correct for issues such as drift, noise, and scan distortion. High-quality analysis and processing using atomic electron tomography results in a 3D reconstruction of an amorphous material detailing the atomic positions of the different species that are present.
Fluctuation electron microscopy
Fluctuation electron microscopy is another transmission electron microscopy-based technique that is sensitive to the medium-range order of amorphous materials. Structural fluctuations arising from different forms of medium-range order can be detected with this method. Fluctuation electron microscopy experiments can be done in conventional or scanning transmission electron microscope mode.
Computational techniques
Simulation and modeling techniques are often combined with experimental methods to characterize structures of amorphous materials. Commonly used computational techniques include density functional theory, molecular dynamics, and reverse Monte Carlo.
Uses and observations | Amorphous solid | Wikipedia | 477 | 2889 | https://en.wikipedia.org/wiki/Amorphous%20solid | Physical sciences | Basics_8 | null |
Amorphous thin films
Amorphous phases are important constituents of thin films. Thin films are solid layers of a few nanometres to tens of micrometres thickness that are deposited onto a substrate. So-called structure zone models were developed to describe the microstructure of thin films as a function of the homologous temperature (Th), which is the ratio of deposition temperature to melting temperature. According to these models, a necessary condition for the occurrence of amorphous phases is that (Th) has to be smaller than 0.3. The deposition temperature must be below 30% of the melting temperature.
Superconductivity
Regarding their applications, amorphous metallic layers played an important role in the discovery of superconductivity in amorphous metals made by Buckel and Hilsch. The superconductivity of amorphous metals, including amorphous metallic thin films, is now understood to be due to phonon-mediated Cooper pairing. The role of structural disorder can be rationalized based on the strong-coupling Eliashberg theory of superconductivity.
Thermal protection
Amorphous solids typically exhibit higher localization of heat carriers compared to crystalline, giving rise to low thermal conductivity. Products for thermal protection, such as thermal barrier coatings and insulation, rely on materials with ultralow thermal conductivity.
Technological uses
Today, optical coatings made from TiO2, SiO2, Ta2O5 etc. (and combinations of these) in most cases consist of amorphous phases of these compounds. Much research is carried out into thin amorphous films as a gas-separating membrane layer. The technologically most important thin amorphous film is probably represented by a few nm thin SiO2 layers serving as isolator above the conducting channel of a metal-oxide semiconductor field-effect transistor (MOSFET). Also, hydrogenated amorphous silicon (Si:H) is of technical significance for thin-film solar cells.
Pharmaceutical use
In the pharmaceutical industry, some amorphous drugs have been shown to offer higher bioavailability than their crystalline counterparts as a result of the higher solubility of the amorphous phase. However, certain compounds can undergo precipitation in their amorphous form in vivo and can then decrease mutual bioavailability if administered together. Studies of GDC-0810 ASDs show a strong interrelationship between microstructure, physical properties and dissolution performance. | Amorphous solid | Wikipedia | 510 | 2889 | https://en.wikipedia.org/wiki/Amorphous%20solid | Physical sciences | Basics_8 | null |
In soils
Amorphous materials in soil strongly influence bulk density, aggregate stability, plasticity, and water holding capacity of soils. The low bulk density and high void ratios are mostly due to glass shards and other porous minerals not becoming compacted. Andisol soils contain the highest amounts of amorphous materials.
Phase
Amorphous phases were a phenomenon of particular interest for the study of thin-film growth. The growth of polycrystalline films is often used and preceded by an initial amorphous layer, the thickness of which may amount to only a few nm. The most investigated example is represented by the unoriented molecules of thin polycrystalline silicon films. Wedge-shaped polycrystals were identified by transmission electron microscopy to grow out of the amorphous phase only after the latter has exceeded a certain thickness, the precise value of which depends on deposition temperature, background pressure, and various other process parameters. The phenomenon has been interpreted in the framework of Ostwald's rule of stages that predicts the formation of phases to proceed with increasing condensation time towards increasing stability. | Amorphous solid | Wikipedia | 227 | 2889 | https://en.wikipedia.org/wiki/Amorphous%20solid | Physical sciences | Basics_8 | null |
In chemistry, an alkali (; from the Arabic word , ) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The adjective alkaline, and less often, alkalescent, is commonly used in English as a synonym for basic, especially for bases soluble in water. This broad use of the term is likely to have come about because alkalis were the first bases known to obey the Arrhenius definition of a base, and they are still among the most common bases.
Etymology
The word alkali is derived from Arabic al qalīy (or alkali), meaning (see calcination), referring to the original source of alkaline substances. A water-extract of burned plant ashes, called potash and composed mostly of potassium carbonate, was mildly basic. After heating this substance with calcium hydroxide (slaked lime), a far more strongly basic substance known as caustic potash (potassium hydroxide) was produced. Caustic potash was traditionally used in conjunction with animal fats to produce soft soaps, one of the caustic processes that rendered soaps from fats in the process of saponification, one known since antiquity. Plant potash lent the name to the element potassium, which was first derived from caustic potash, and also gave potassium its chemical symbol K (from the German name ), which ultimately derived from alkali.
Common properties of alkalis and bases
Alkalis are all Arrhenius bases, ones which form hydroxide ions (OH−) when dissolved in water. Common properties of alkaline aqueous solutions include:
Moderately concentrated solutions (over 10−3 M) have a pH of 10 or greater. This means that they will turn phenolphthalein from colorless to pink.
Concentrated solutions are caustic (causing chemical burns).
Alkaline solutions are slippery or soapy to the touch, due to the saponification of the fatty substances on the surface of the skin.
Alkalis are normally water-soluble, although some like barium carbonate are only soluble when reacting with an acidic aqueous solution.
Difference between alkali and base
The terms "base" and "alkali" are often used interchangeably, particularly outside the context of chemistry and chemical engineering. | Alkali | Wikipedia | 512 | 2955 | https://en.wikipedia.org/wiki/Alkali | Physical sciences | Concepts | Chemistry |
There are various, more specific definitions for the concept of an alkali. Alkalis are usually defined as a subset of the bases. One of two subsets is commonly chosen.
A basic salt of an alkali metal or alkaline earth metal (this includes Mg(OH)2 (magnesium hydroxide) but excludes NH3 (ammonia)).
Any base that is soluble in water and forms hydroxide ions or the solution of a base in water. (This includes both Mg(OH)2 and NH3, which forms NH4OH.)
The second subset of bases is also called an "Arrhenius base".
Alkali salts
Alkali salts are soluble hydroxides of alkali metals and alkaline earth metals, of which common examples are:
Sodium hydroxide (NaOH) – often called "caustic soda"
Potassium hydroxide (KOH) – commonly called "caustic potash"
Lye – generic term for either of two previous salts or their mixture
Calcium hydroxide (Ca(OH)2) – saturated solution known as "limewater"
Magnesium hydroxide (Mg(OH)2) – an atypical alkali since it has low solubility in water (although the dissolved portion is considered a strong base due to complete dissociation of its ions)
Alkaline soil
Soils with pH values that are higher than 7.3 are usually defined as being alkaline. These soils can occur naturally due to the presence of alkali salts. Although many plants do prefer slightly basic soil (including vegetables like cabbage and fodder like buffalo grass), most plants prefer mildly acidic soil (with pHs between 6.0 and 6.8), and alkaline soils can cause problems.
Alkali lakes
In alkali lakes (also called soda lakes), evaporation concentrates the naturally occurring carbonate salts, giving rise to an alkalic and often saline lake.
Examples of alkali lakes:
Alkali Lake, Lake County, Oregon
Baldwin Lake, San Bernardino County, California
Bear Lake on the Utah–Idaho border
Lake Magadi in Kenya
Lake Turkana in Kenya
Mono Lake, near Owens Valley in California
Redberry Lake, Saskatchewan
Summer Lake, Lake County, Oregon
Tramping Lake, Saskatchewan | Alkali | Wikipedia | 463 | 2955 | https://en.wikipedia.org/wiki/Alkali | Physical sciences | Concepts | Chemistry |
Alcoholism is the continued drinking of alcohol despite it causing problems. Some definitions require evidence of dependence and withdrawal. Problematic use of alcohol has been mentioned in the earliest historical records. The World Health Organization (WHO) estimated there were 283 million people with alcohol use disorders worldwide . The term alcoholism was first coined in 1852, but alcoholism and alcoholic are sometimes considered stigmatizing and to discourage seeking treatment, so diagnostic terms such as alcohol use disorder or alcohol dependence are often used instead in a clinical context.
Alcohol is addictive, and heavy long-term alcohol use results in many negative health and social consequences. It can damage all the organ systems, but especially affects the brain, heart, liver, pancreas and immune system. Heavy alcohol usage can result in trouble sleeping, and severe cognitive issues like dementia, brain damage, or Wernicke–Korsakoff syndrome. Physical effects include irregular heartbeat, an impaired immune response, liver cirrhosis, increased cancer risk, and severe withdrawal symptoms if stopped suddenly. These health effects can reduce life expectancy by 10 years. Drinking during pregnancy may harm the child's health, and drunk driving increases the risk of traffic accidents. Alcoholism is also associated with increases in violent and non-violent crime. While alcoholism directly resulted in 139,000 deaths worldwide in 2013, in 2012 3.3 million deaths may be attributable globally to alcohol.
The development of alcoholism is attributed to both environment and genetics equally. The use of alcohol to self-medicate stress or anxiety can turn into alcoholism. Someone with a parent or sibling with an alcohol use disorder is three to four times more likely to develop an alcohol use disorder themselves, but only a minority of them do. Environmental factors include social, cultural and behavioral influences. High stress levels and anxiety, as well as alcohol's inexpensive cost and easy accessibility, increase the risk. People may continue to drink partly to prevent or improve symptoms of withdrawal. After a person stops drinking alcohol, they may experience a low level of withdrawal lasting for months. Medically, alcoholism is considered both a physical and mental illness. Questionnaires are usually used to detect possible alcoholism. Further information is then collected to confirm the diagnosis. | Alcoholism | Wikipedia | 442 | 2965 | https://en.wikipedia.org/wiki/Alcoholism | Biology and health sciences | Drugs and medication | null |
Treatment of alcoholism may take several forms. Due to medical problems that can occur during withdrawal, alcohol cessation should be controlled carefully. One common method involves the use of benzodiazepine medications, such as diazepam. These can be taken while admitted to a health care institution or individually. The medications acamprosate or disulfiram may also be used to help prevent further drinking. Mental illness or other addictions may complicate treatment. Various individual or group therapy or support groups are used to attempt to keep a person from returning to alcoholism. Among them is the abstinence based mutual aid fellowship Alcoholics Anonymous (AA). A 2020 scientific review found that clinical interventions encouraging increased participation in AA (AA/twelve step facilitation (AA/TSF))—resulted in higher abstinence rates over other clinical interventions, and most studies in the review found that AA/TSF led to lower health costs.
Many terms, some slurs and some informal, have been used to refer to people affected by alcoholism such as tippler, drunkard, dipsomaniac and souse.
Signs and symptoms
The risk of alcohol dependence begins at low levels of drinking and increases directly with both the volume of alcohol consumed and a pattern of drinking larger amounts on an occasion, to the point of intoxication, which is sometimes called binge drinking. Binge drinking is the most common pattern of alcoholism. It has different definitions and one of this defines it as a pattern of drinking when a male has five or more drinks on an occasion or a female has at least four drinks on an occasion.
Long-term misuse
Alcoholism is characterized by an increased tolerance to alcohol – which means that an individual can consume more alcohol – and physical dependence on alcohol, which makes it hard for an individual to control their consumption. The physical dependency caused by alcohol can lead to an affected individual having a very strong urge to drink alcohol. These characteristics play a role in decreasing the ability to stop drinking of an individual with an alcohol use disorder. Alcoholism can have adverse effects on mental health, contributing to psychiatric disorders and increasing the risk of suicide. A depressed mood is a common symptom of heavy alcohol drinkers. | Alcoholism | Wikipedia | 450 | 2965 | https://en.wikipedia.org/wiki/Alcoholism | Biology and health sciences | Drugs and medication | null |
Warning signs
Warning signs of alcoholism include the consumption of increasing amounts of alcohol and frequent intoxication, preoccupation with drinking to the exclusion of other activities, promises to quit drinking and failure to keep those promises, the inability to remember what was said or done while drinking (colloquially known as "blackouts"), personality changes associated with drinking, denial or the making of excuses for drinking, the refusal to admit excessive drinking, dysfunction or other problems at work or school, the loss of interest in personal appearance or hygiene, marital and economic problems, and the complaint of poor health, with loss of appetite, respiratory infections, or increased anxiety.
Physical
Short-term effects
Drinking enough to cause a blood alcohol concentration (BAC) of 0.03–0.12% typically causes an overall improvement in mood and possible euphoria (intense feelings of well-being and happiness), increased self-confidence and sociability, decreased anxiety, a flushed, red appearance in the face and impaired judgment and fine muscle coordination. A BAC of 0.09% to 0.25% causes lethargy, sedation, balance problems and blurred vision. A BAC of 0.18% to 0.30% causes profound confusion, impaired speech (e.g. slurred speech), staggering, dizziness and vomiting. A BAC from 0.25% to 0.40% causes stupor, unconsciousness, anterograde amnesia, vomiting (death may occur due to inhalation of vomit while unconscious) and respiratory depression (potentially life-threatening). A BAC from 0.35% to 0.80% causes a coma (unconsciousness), life-threatening respiratory depression and possibly fatal alcohol poisoning. With all alcoholic beverages, drinking while driving, operating an aircraft or heavy machinery increases the risk of an accident; many countries have penalties for drunk driving.
Long-term effects | Alcoholism | Wikipedia | 387 | 2965 | https://en.wikipedia.org/wiki/Alcoholism | Biology and health sciences | Drugs and medication | null |
Having more than one drink a day for women or two drinks for men increases the risk of heart disease, high blood pressure, atrial fibrillation, and stroke. Risk is greater with binge drinking, which may also result in violence or accidents. About 3.3 million deaths (5.9% of all deaths) are believed to be due to alcohol each year. Alcoholism reduces a person's life expectancy by around ten years and alcohol use is the third leading cause of early death in the United States. Long-term alcohol misuse can cause a number of physical symptoms, including cirrhosis of the liver, pancreatitis, epilepsy, polyneuropathy, alcoholic dementia, heart disease, nutritional deficiencies, peptic ulcers and sexual dysfunction, and can eventually be fatal. Other physical effects include an increased risk of developing cardiovascular disease, malabsorption, alcoholic liver disease, and several cancers such as breast cancer and head and neck cancer. Damage to the central nervous system and peripheral nervous system can occur from sustained alcohol consumption. A wide range of immunologic defects can result and there may be a generalized skeletal fragility, in addition to a recognized tendency to accidental injury, resulting in a propensity for bone fractures.
Women develop long-term complications of alcohol dependence more rapidly than do men, women also have a higher mortality rate from alcoholism than men. Examples of long-term complications include brain, heart, and liver damage and an increased risk of breast cancer. Additionally, heavy drinking over time has been found to have a negative effect on reproductive functioning in women. This results in reproductive dysfunction such as anovulation, decreased ovarian mass, problems or irregularity of the menstrual cycle, and early menopause. Alcoholic ketoacidosis can occur in individuals who chronically misuse alcohol and have a recent history of binge drinking. The amount of alcohol that can be biologically processed and its effects differ between sexes. Equal dosages of alcohol consumed by men and women generally result in women having higher blood alcohol concentrations (BACs), since women generally have a lower weight and higher percentage of body fat and therefore a lower volume of distribution for alcohol than men. | Alcoholism | Wikipedia | 455 | 2965 | https://en.wikipedia.org/wiki/Alcoholism | Biology and health sciences | Drugs and medication | null |
Psychiatric
Long-term misuse of alcohol can cause a wide range of mental health problems. Severe cognitive problems are common; approximately 10% of all dementia cases are related to alcohol consumption, making it the second leading cause of dementia. Excessive alcohol use causes damage to brain function, and psychological health can be increasingly affected over time. Social skills are significantly impaired in people with alcoholism due to the neurotoxic effects of alcohol on the brain, especially the prefrontal cortex area of the brain. The social skills that are impaired by alcohol use disorder include impairments in perceiving facial emotions, prosody, perception problems, and theory of mind deficits; the ability to understand humor is also impaired in people who misuse alcohol. Psychiatric disorders are common in people with alcohol use disorders, with as many as 25% also having severe psychiatric disturbances. The most prevalent psychiatric symptoms are anxiety and depression disorders. Psychiatric symptoms usually initially worsen during alcohol withdrawal, but typically improve or disappear with continued abstinence. Psychosis, confusion, and organic brain syndrome may be caused by alcohol misuse, which can lead to a misdiagnosis such as schizophrenia. Panic disorder can develop or worsen as a direct result of long-term alcohol misuse.
The co-occurrence of major depressive disorder and alcoholism is well documented. Among those with comorbid occurrences, a distinction is commonly made between depressive episodes that remit with alcohol abstinence ("substance-induced"), and depressive episodes that are primary and do not remit with abstinence ("independent" episodes). Additional use of other drugs may increase the risk of depression. Psychiatric disorders differ depending on gender. Women who have alcohol-use disorders often have a co-occurring psychiatric diagnosis such as major depression, anxiety, panic disorder, bulimia, post-traumatic stress disorder (PTSD), or borderline personality disorder. Men with alcohol-use disorders more often have a co-occurring diagnosis of narcissistic or antisocial personality disorder, bipolar disorder, schizophrenia, impulse disorders or attention deficit/hyperactivity disorder (ADHD). Women with alcohol use disorder are more likely to experience physical or sexual assault, abuse, and domestic violence than women in the general population, which can lead to higher instances of psychiatric disorders and greater dependence on alcohol.
Social effects | Alcoholism | Wikipedia | 478 | 2965 | https://en.wikipedia.org/wiki/Alcoholism | Biology and health sciences | Drugs and medication | null |
Serious social problems arise from alcohol use disorder; these dilemmas are caused by the pathological changes in the brain and the intoxicating effects of alcohol. Alcohol misuse is associated with an increased risk of committing criminal offences, including child abuse, domestic violence, rape, burglary and assault. Alcoholism is associated with loss of employment, which can lead to financial problems. Drinking at inappropriate times and behavior caused by reduced judgment can lead to legal consequences, such as criminal charges for drunk driving or public disorder, or civil penalties for tortious behavior. An alcoholic's behavior and mental impairment while drunk can profoundly affect those surrounding him and lead to isolation from family and friends. This isolation can lead to marital conflict and divorce, or contribute to domestic violence. Alcoholism can also lead to child neglect, with subsequent lasting damage to the emotional development of children of people with alcohol use disorders. For this reason, children of people with alcohol use disorders can develop a number of emotional problems. For example, they can become afraid of their parents, because of their unstable mood behaviors. They may develop shame over their inadequacy to liberate their parents from alcoholism and, as a result of this, may develop self-image problems, which can lead to depression.
Alcohol withdrawal
As with similar substances with a sedative-hypnotic mechanism, such as barbiturates and benzodiazepines, withdrawal from alcohol dependence can be fatal if it is not properly managed. Alcohol's primary effect is the increase in stimulation of the GABAA receptor, promoting central nervous system depression. With repeated heavy consumption of alcohol, these receptors are desensitized and reduced in number, resulting in tolerance and physical dependence. When alcohol consumption is stopped too abruptly, the person's nervous system experiences uncontrolled synapse firing. This can result in symptoms that include anxiety, life-threatening seizures, delirium tremens, hallucinations, shakes and possible heart failure. Other neurotransmitter systems are also involved, especially dopamine, NMDA and glutamate.
Severe acute withdrawal symptoms such as delirium tremens and seizures rarely occur after 1-week post cessation of alcohol. The acute withdrawal phase can be defined as lasting between one and three weeks. In the period of 3–6 weeks following cessation, anxiety, depression, fatigue, and sleep disturbance are common. Similar post-acute withdrawal symptoms have also been observed in animal models of alcohol dependence and withdrawal. | Alcoholism | Wikipedia | 510 | 2965 | https://en.wikipedia.org/wiki/Alcoholism | Biology and health sciences | Drugs and medication | null |
A kindling effect also occurs in people with alcohol use disorders whereby each subsequent withdrawal syndrome is more severe than the previous withdrawal episode; this is due to neuroadaptations which occur as a result of periods of abstinence followed by re-exposure to alcohol. Individuals who have had multiple withdrawal episodes are more likely to develop seizures and experience more severe anxiety during withdrawal from alcohol than alcohol-dependent individuals without a history of past alcohol withdrawal episodes. The kindling effect leads to persistent functional changes in brain neural circuits as well as to gene expression. Kindling also results in the intensification of psychological symptoms of alcohol withdrawal. There are decision tools and questionnaires that help guide physicians in evaluating alcohol withdrawal. For example, the CIWA-Ar objectifies alcohol withdrawal symptoms in order to guide therapy decisions which allows for an efficient interview while at the same time retaining clinical usefulness, validity, and reliability, ensuring proper care for withdrawal patients, who can be in danger of death.
Causes
A complex combination of genetic and environmental factors influences the risk of the development of alcoholism. Genes that influence the metabolism of alcohol also influence the risk of alcoholism, as can a family history of alcoholism. There is compelling evidence that alcohol use at an early age may influence the expression of genes which increase the risk of alcohol dependence. These genetic and epigenetic results are regarded as consistent with large longitudinal population studies finding that the younger the age of drinking onset, the greater the prevalence of lifetime alcohol dependence.
Severe childhood trauma is also associated with a general increase in the risk of drug dependency. Lack of peer and family support is associated with an increased risk of alcoholism developing. Genetics and adolescence are associated with an increased sensitivity to the neurotoxic effects of chronic alcohol misuse. Cortical degeneration due to the neurotoxic effects increases impulsive behaviour, which may contribute to the development, persistence and severity of alcohol use disorders. There is evidence that with abstinence, there is a reversal of at least some of the alcohol induced central nervous system damage. The use of cannabis was associated with later problems with alcohol use. Alcohol use was associated with an increased probability of later use of tobacco and illegal drugs such as cannabis.
Availability
Alcohol is the most available, widely consumed, and widely misused recreational drug. Beer alone is the world's most widely consumed alcoholic beverage; it is the third-most popular drink overall, after water and tea. It is thought by some to be the oldest fermented beverage.
Gender difference | Alcoholism | Wikipedia | 509 | 2965 | https://en.wikipedia.org/wiki/Alcoholism | Biology and health sciences | Drugs and medication | null |
Based on combined data in the US from SAMHSA's 2004–2005 National Surveys on Drug Use & Health, the rate of past-year alcohol dependence or misuse among persons aged 12 or older varied by level of alcohol use: 44.7% of past month heavy drinkers, 18.5% binge drinkers, 3.8% past month non-binge drinkers, and 1.3% of those who did not drink alcohol in the past month met the criteria for alcohol dependence or misuse in the past year. Males had higher rates than females for all measures of drinking in the past month: any alcohol use (57.5% vs. 45%), binge drinking (30.8% vs. 15.1%), and heavy alcohol use (10.5% vs. 3.3%), and males were twice as likely as females to have met the criteria for alcohol dependence or misuse in the past year (10.5% vs. 5.1%). However, because females generally weigh less than males, have more fat and less water in their bodies, and metabolize less alcohol in their esophagus and stomach, they are likely to develop higher blood alcohol levels per drink. Women may also be more vulnerable to liver disease.
Genetic variation | Alcoholism | Wikipedia | 269 | 2965 | https://en.wikipedia.org/wiki/Alcoholism | Biology and health sciences | Drugs and medication | null |
There are genetic variations that affect the risk for alcoholism. Some of these variations are more common in individuals with ancestry from certain areas; for example, Africa, East Asia, the Middle East and Europe. The variants with strongest effect are in genes that encode the main enzymes of alcohol metabolism, ADH1B and ALDH2. These genetic factors influence the rate at which alcohol and its initial metabolic product, acetaldehyde, are metabolized. They are found at different frequencies in people from different parts of the world. The alcohol dehydrogenase allele ADH1B*2 causes a more rapid metabolism of alcohol to acetaldehyde, and reduces risk for alcoholism; it is most common in individuals from East Asia and the Middle East. The alcohol dehydrogenase allele ADH1B*3 also causes a more rapid metabolism of alcohol. The allele ADH1B*3 is only found in some individuals of African descent and certain Native American tribes. African Americans and Native Americans with this allele have a reduced risk of developing alcoholism. Native Americans, however, have a significantly higher rate of alcoholism than average; risk factors such as cultural environmental effects (e.g. trauma) have been proposed to explain the higher rates. The aldehyde dehydrogenase allele ALDH2*2 greatly reduces the rate at which acetaldehyde, the initial product of alcohol metabolism, is removed by conversion to acetate; it greatly reduces the risk for alcoholism.
A genome-wide association study (GWAS) of more than 100,000 human individuals identified variants of the gene KLB, which encodes the transmembrane protein β-Klotho, as highly associated with alcohol consumption. The protein β-Klotho is an essential element in cell surface receptors for hormones involved in modulation of appetites for simple sugars and alcohol. Several large GWAS have found differences in the genetics of alcohol consumption and alcohol dependence, although the two are to some degree related.
DNA damage | Alcoholism | Wikipedia | 411 | 2965 | https://en.wikipedia.org/wiki/Alcoholism | Biology and health sciences | Drugs and medication | null |
Alcohol-induced DNA damage, when not properly repaired, may have a key role in the neurotoxicity induced by alcohol. Metabolic conversion of ethanol to acetaldehyde can occur in the brain and the neurotoxic effects of ethanol appear to be associated with acetaldehyde induced DNA damages including DNA adducts and crosslinks. In addition to acetaldehyde, alcohol metabolism produces potentially genotoxic reactive oxygen species, which have been demonstrated to cause oxidative DNA damage.
Diagnosis
Definition
Because there is disagreement on the definition of the word alcoholism, it is not a recognized diagnosis, and the use of the term alcoholism is discouraged due to its heavily stigmatized connotations. It is classified as alcohol use disorder in the DSM-5 or alcohol dependence in the ICD-11. In 1979, the World Health Organization discouraged the use of alcoholism due to its inexact meaning, preferring alcohol dependence syndrome. | Alcoholism | Wikipedia | 193 | 2965 | https://en.wikipedia.org/wiki/Alcoholism | Biology and health sciences | Drugs and medication | null |
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