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Astatine is known to react with its lighter homologs iodine, bromine, and chlorine in the vapor state; these reactions produce diatomic interhalogen compounds with formulas AtI, AtBr, and AtCl. The first two compounds may also be produced in water – astatine reacts with iodine/iodide solution to form AtI, whereas AtBr ... | Astatine | Wikipedia | 508 | 901 | https://en.wikipedia.org/wiki/Astatine | Physical sciences | Chemical elements_2 | null |
The first claimed discovery of eka-iodine was made by Fred Allison and his associates at the Alabama Polytechnic Institute (now Auburn University) in 1931. The discoverers named element 85 "alabamine", and assigned it the symbol Ab, designations that were used for a few years. In 1934, H. G. MacPherson of University of... | Astatine | Wikipedia | 496 | 901 | https://en.wikipedia.org/wiki/Astatine | Physical sciences | Chemical elements_2 | null |
In 1940, the Swiss chemist Walter Minder announced the discovery of element 85 as the beta decay product of radium A (polonium-218), choosing the name "helvetium" (from , the Latin name of Switzerland). Berta Karlik and Traude Bernert were unsuccessful in reproducing his experiments, and subsequently attributed Minder'... | Astatine | Wikipedia | 173 | 901 | https://en.wikipedia.org/wiki/Astatine | Physical sciences | Chemical elements_2 | null |
Later in 1940, Dale R. Corson, Kenneth Ross MacKenzie, and Emilio Segrè isolated the element at the University of California, Berkeley. Instead of searching for the element in nature, the scientists created it by bombarding bismuth-209 with alpha particles in a cyclotron (particle accelerator) to produce, after emissio... | Astatine | Wikipedia | 498 | 901 | https://en.wikipedia.org/wiki/Astatine | Physical sciences | Chemical elements_2 | null |
Astatine's alpha decay energies follow the same trend as for other heavy elements. Lighter astatine isotopes have quite high energies of alpha decay, which become lower as the nuclei become heavier. Astatine-211 has a significantly higher energy than the previous isotope, because it has a nucleus with 126 neutrons, and... | Astatine | Wikipedia | 442 | 901 | https://en.wikipedia.org/wiki/Astatine | Physical sciences | Chemical elements_2 | null |
Astatine has 24 known nuclear isomers, which are nuclei with one or more nucleons (protons or neutrons) in an excited state. A nuclear isomer may also be called a "meta-state", meaning the system has more internal energy than the "ground state" (the state with the lowest possible internal energy), making the former lik... | Astatine | Wikipedia | 497 | 901 | https://en.wikipedia.org/wiki/Astatine | Physical sciences | Chemical elements_2 | null |
Isotopes of astatine are sometimes not listed as naturally occurring because of misconceptions that there are no such isotopes, or discrepancies in the literature. Astatine-216 has been counted as a naturally occurring isotope but reports of its observation (which were described as doubtful) have not been confirmed.
S... | Astatine | Wikipedia | 271 | 901 | https://en.wikipedia.org/wiki/Astatine | Physical sciences | Chemical elements_2 | null |
The most important isotope is astatine-211, the only one in commercial use. To produce the bismuth target, the metal is sputtered onto a gold, copper, or aluminium surface at 50 to 100 milligrams per square centimeter. Bismuth oxide can be used instead; this is forcibly fused with a copper plate. The target is kept und... | Astatine | Wikipedia | 380 | 901 | https://en.wikipedia.org/wiki/Astatine | Physical sciences | Chemical elements_2 | null |
Dry
The astatine-containing cyclotron target is heated to a temperature of around 650 °C. The astatine volatilizes and is condensed in (typically) a cold trap. Higher temperatures of up to around 850 °C may increase the yield, at the risk of bismuth contamination from concurrent volatilization. Redistilling the conden... | Astatine | Wikipedia | 479 | 901 | https://en.wikipedia.org/wiki/Astatine | Physical sciences | Chemical elements_2 | null |
Newly formed astatine-211 is the subject of ongoing research in nuclear medicine. It must be used quickly as it decays with a half-life of 7.2 hours; this is long enough to permit multistep labeling strategies. Astatine-211 has potential for targeted alpha-particle therapy, since it decays either via emission of an alp... | Astatine | Wikipedia | 374 | 901 | https://en.wikipedia.org/wiki/Astatine | Physical sciences | Chemical elements_2 | null |
Several obstacles have been encountered in the development of astatine-based radiopharmaceuticals for cancer treatment. World War II delayed research for close to a decade. Results of early experiments indicated that a cancer-selective carrier would need to be developed and it was not until the 1970s that monoclonal an... | Astatine | Wikipedia | 481 | 901 | https://en.wikipedia.org/wiki/Astatine | Physical sciences | Chemical elements_2 | null |
Atoms are the basic particles of the chemical elements. An atom consists of a nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished from each other by the number of protons that are in their atoms. For example, any atom that co... | Atom | Wikipedia | 468 | 902 | https://en.wikipedia.org/wiki/Atom | Physical sciences | Science and medicine | null |
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". But this ancient idea was based in philosophical reasoning rather than scientific reasoning. Modern atomic the... | Atom | Wikipedia | 371 | 902 | https://en.wikipedia.org/wiki/Atom | Physical sciences | Science and medicine | null |
Dalton also analyzed iron oxides. There is one type of iron oxide that is a black powder which is 78.1% iron and 21.9% oxygen; and there is another iron oxide that is a red powder 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, an... | Atom | Wikipedia | 511 | 902 | https://en.wikipedia.org/wiki/Atom | Physical sciences | Science and medicine | null |
The electrons in the atom logically had to be balanced out by a commensurate amount of positive charge, but Thomson had no idea where this positive charge came from, so he tentatively proposed that it was everywhere in the atom, the atom being in the shape of a sphere. This was the mathematically simplest hypothesis to... | Atom | Wikipedia | 360 | 902 | https://en.wikipedia.org/wiki/Atom | Physical sciences | Science and medicine | null |
A problem in classical mechanics is that an accelerating charged particle radiates electromagnetic radiation, causing the particle to lose kinetic energy. Circular motion counts as acceleration, which means that an electron orbiting a central charge should spiral down into that nucleus as it loses speed. In 1913, the p... | Atom | Wikipedia | 476 | 902 | https://en.wikipedia.org/wiki/Atom | Physical sciences | Science and medicine | 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 ha... | Atom | Wikipedia | 466 | 902 | https://en.wikipedia.org/wiki/Atom | Physical sciences | Science and medicine | null |
The electron is the least massive of these particles by four orders of magnitude at , with a negative electrical charge and a size that is too small to be measured using available techniques. It was the lightest particle with a positive rest mass measured, until the discovery of neutrino mass. Under ordinary conditions... | Atom | Wikipedia | 510 | 902 | https://en.wikipedia.org/wiki/Atom | Physical sciences | Science and medicine | null |
All the bound protons and neutrons in an atom make up a tiny atomic nucleus, and are collectively called nucleons. The radius of a nucleus is approximately equal to femtometres, where is the total number of nucleons. This is much smaller than the radius of the atom, which is on the order of 105 fm. The nucleons are b... | Atom | Wikipedia | 376 | 902 | https://en.wikipedia.org/wiki/Atom | Physical sciences | Science and medicine | null |
The number of protons and neutrons in the atomic nucleus can be modified, although this can require very high energies because of the strong force. Nuclear fusion occurs when multiple atomic particles join to form a heavier nucleus, such as through the energetic collision of two nuclei. For example, at the core of the ... | Atom | Wikipedia | 431 | 902 | https://en.wikipedia.org/wiki/Atom | Physical sciences | Science and medicine | null |
The electrons in an atom are attracted to the protons in the nucleus by the electromagnetic force. This force binds the electrons inside an electrostatic potential well surrounding the smaller nucleus, which means that an external source of energy is needed for the electron to escape. The closer an electron is to the n... | Atom | Wikipedia | 465 | 902 | https://en.wikipedia.org/wiki/Atom | Physical sciences | Science and medicine | null |
By definition, any two atoms with an identical number of protons in their nuclei belong to the same chemical element. Atoms with equal numbers of protons but a different number of neutrons are different isotopes of the same element. For example, all hydrogen atoms admit exactly one proton, but isotopes exist with no ne... | Atom | Wikipedia | 467 | 902 | https://en.wikipedia.org/wiki/Atom | Physical sciences | Science and medicine | null |
Stability of isotopes is affected by the ratio of protons to neutrons, and also by the presence of certain "magic numbers" of neutrons or protons that represent closed and filled quantum shells. These quantum shells correspond to a set of energy levels within the shell model of the nucleus; filled shells, such as the f... | Atom | Wikipedia | 347 | 902 | https://en.wikipedia.org/wiki/Atom | Physical sciences | Science and medicine | null |
The actual mass of an atom at rest is often expressed in daltons (Da), also called the unified atomic mass unit (u). This unit is defined as a twelfth of the mass of a free neutral atom of carbon-12, which is approximately . Hydrogen-1 (the lightest isotope of hydrogen which is also the nuclide with the lowest mass) ha... | Atom | Wikipedia | 475 | 902 | https://en.wikipedia.org/wiki/Atom | Physical sciences | Science and medicine | null |
When subjected to external forces, like electrical fields, the shape of an atom may deviate from spherical symmetry. The deformation depends on the field magnitude and the orbital type of outer shell electrons, as shown by group-theoretical considerations. Aspherical deviations might be elicited for instance in crystal... | Atom | Wikipedia | 313 | 902 | https://en.wikipedia.org/wiki/Atom | Physical sciences | Science and medicine | null |
The most common forms of radioactive decay are:
Alpha decay: this process is caused when the nucleus emits an alpha particle, which is a helium nucleus consisting of two protons and two neutrons. The result of the emission is a new element with a lower atomic number.
Beta decay (and electron capture): these processes... | Atom | Wikipedia | 477 | 902 | https://en.wikipedia.org/wiki/Atom | Physical sciences | Science and medicine | null |
Elementary particles possess an intrinsic quantum mechanical property known as spin. This is analogous to the angular momentum of an object that is spinning around its center of mass, although strictly speaking these particles are believed to be point-like and cannot be said to be rotating. Spin is measured in units of... | Atom | Wikipedia | 490 | 902 | https://en.wikipedia.org/wiki/Atom | Physical sciences | Science and medicine | null |
The potential energy of an electron in an atom is negative relative to when the distance from the nucleus goes to infinity; its dependence on the electron's position reaches the minimum inside the nucleus, roughly in inverse proportion to the distance. In the quantum-mechanical model, a bound electron can occupy only a... | Atom | Wikipedia | 368 | 902 | https://en.wikipedia.org/wiki/Atom | Physical sciences | Science and medicine | null |
When a continuous spectrum of energy is passed through a gas or plasma, some of the photons are absorbed by atoms, causing electrons to change their energy level. Those excited electrons that remain bound to their atom spontaneously emit this energy as a photon, traveling in a random direction, and so drop back to lowe... | Atom | Wikipedia | 432 | 902 | https://en.wikipedia.org/wiki/Atom | Physical sciences | Science and medicine | null |
Valency is the combining power of an element. It is determined by the number of bonds it can form to other atoms or groups. The outermost electron shell of an atom in its uncombined state is known as the valence shell, and the electrons in
that shell are called valence electrons. The number of valence electrons determi... | Atom | Wikipedia | 467 | 902 | https://en.wikipedia.org/wiki/Atom | Physical sciences | Science and medicine | null |
While atoms are too small to be seen, devices such as the scanning tunneling microscope (STM) enable their visualization at the surfaces of solids. The microscope uses the quantum tunneling phenomenon, which allows particles to pass through a barrier that would be insurmountable in the classical perspective. Electrons ... | Atom | Wikipedia | 412 | 902 | https://en.wikipedia.org/wiki/Atom | Physical sciences | Science and medicine | null |
Electron emission techniques such as X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES), which measure the binding energies of the core electrons, are used to identify the atomic species present in a sample in a non-destructive way. With proper focusing both can be made area-specific. Another ... | Atom | Wikipedia | 493 | 902 | https://en.wikipedia.org/wiki/Atom | Physical sciences | Science and medicine | null |
Ubiquitousness and stability of atoms relies on their binding energy, which means that an atom has a lower energy than an unbound system of the nucleus and electrons. Where the temperature is much higher than ionization potential, the matter exists in the form of plasma—a gas of positively charged ions (possibly, bare ... | Atom | Wikipedia | 405 | 902 | https://en.wikipedia.org/wiki/Atom | Physical sciences | Science and medicine | null |
There are a few trace atoms on Earth that were not present at the beginning (i.e., not "primordial"), nor are results of radioactive decay. Carbon-14 is continuously generated by cosmic rays in the atmosphere. Some atoms on Earth have been artificially generated either deliberately or as by-products of nuclear reactors... | Atom | Wikipedia | 457 | 902 | https://en.wikipedia.org/wiki/Atom | Physical sciences | Science and medicine | null |
Each particle of matter has a corresponding antimatter particle with the opposite electrical charge. Thus, the positron is a positively charged antielectron and the antiproton is a negatively charged equivalent of a proton. When a matter and corresponding antimatter particle meet, they annihilate each other. Because of... | Atom | Wikipedia | 221 | 902 | https://en.wikipedia.org/wiki/Atom | Physical sciences | Science and medicine | null |
Arable land (from the , "able to be ploughed") is any land capable of being ploughed and used to grow crops. Alternatively, for the purposes of agricultural statistics, the term often has a more precise definition:
A more concise definition appearing in the Eurostat glossary similarly refers to actual rather than pot... | Arable land | Wikipedia | 302 | 903 | https://en.wikipedia.org/wiki/Arable%20land | Technology | Basics_2 | null |
Other non-arable land includes land that is not suitable for any agricultural use. Land that is not arable, in the sense of lacking capability or suitability for cultivation for crop production, has one or more limitationsa lack of sufficient freshwater for irrigation, stoniness, steepness, adverse climate, excessive w... | Arable land | Wikipedia | 429 | 903 | https://en.wikipedia.org/wiki/Arable%20land | Technology | Basics_2 | null |
The use of artifices does not make the land arable. Rock still remains rock, and shallowless than turnable soil is still not considered toilable. The use of artifice is an open-air non-recycled water hydroponics relationship. The below described circumstances are not in perspective, have limited duration, and have a te... | Arable land | Wikipedia | 490 | 903 | https://en.wikipedia.org/wiki/Arable%20land | Technology | Basics_2 | null |
Aluminium (or aluminum in North American English) is a chemical element; it has symbol Al and atomic number 13. Aluminium has a density lower than that of other common metals, about one-third that of steel. It has a great affinity towards oxygen, forming a protective layer of oxide on the surface when exposed to air. A... | Aluminium | Wikipedia | 497 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
Of aluminium isotopes, only is stable. This situation is common for elements with an odd atomic number. It is the only primordial aluminium isotope, i.e. the only one that has existed on Earth in its current form since the formation of the planet. It is therefore a mononuclidic element and its standard atomic weight i... | Aluminium | Wikipedia | 464 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
A free aluminium atom has a radius of 143 pm. With the three outermost electrons removed, the radius shrinks to 39 pm for a 4-coordinated atom or 53.5 pm for a 6-coordinated atom. At standard temperature and pressure, aluminium atoms (when not affected by atoms of other elements) form a face-centered cubic crystal syst... | Aluminium | Wikipedia | 486 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
Pure aluminium is quite soft and lacking in strength. In most applications various aluminium alloys are used instead because of their higher strength and hardness. The yield strength of pure aluminium is 7–11 MPa, while aluminium alloys have yield strengths ranging from 200 MPa to 600 MPa. Aluminium is ductile, with a ... | Aluminium | Wikipedia | 326 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
The underlying core under aluminium's valence shell is that of the preceding noble gas, whereas those of its heavier congeners gallium, indium, thallium, and nihonium also include a filled d-subshell and in some cases a filled f-subshell. Hence, the inner electrons of aluminium shield the valence electrons almost compl... | Aluminium | Wikipedia | 383 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
In hot concentrated hydrochloric acid, aluminium reacts with water with evolution of hydrogen, and in aqueous sodium hydroxide or potassium hydroxide at room temperature to form aluminates—protective passivation under these conditions is negligible. Aqua regia also dissolves aluminium. Aluminium is corroded by dissolve... | Aluminium | Wikipedia | 436 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
Aluminium hydroxide forms both salts and aluminates and dissolves in acid and alkali, as well as on fusion with acidic and basic oxides. This behavior of Al(OH)3 is termed amphoterism and is characteristic of weakly basic cations that form insoluble hydroxides and whose hydrated species can also donate their protons. O... | Aluminium | Wikipedia | 400 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
With heavier halides, the coordination numbers are lower. The other trihalides are dimeric or polymeric with tetrahedral four-coordinate aluminium centers. Aluminium trichloride (AlCl3) has a layered polymeric structure below its melting point of but transforms on melting to Al2Cl6 dimers. At higher temperatures those... | Aluminium | Wikipedia | 239 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
Aluminium forms one stable oxide with the chemical formula Al2O3, commonly called alumina. It can be found in nature in the mineral corundum, α-alumina; there is also a γ-alumina phase. Its crystalline form, corundum, is very hard (Mohs hardness 9), has a high melting point of , has very low volatility, is chemically i... | Aluminium | Wikipedia | 336 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
The only stable chalcogenides under normal conditions are aluminium sulfide (Al2S3), selenide (Al2Se3), and telluride (Al2Te3). All three are prepared by direct reaction of their elements at about and quickly hydrolyze completely in water to yield aluminium hydroxide and the respective hydrogen chalcogenide. As alumin... | Aluminium | Wikipedia | 361 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
There are few compounds with lower oxidation states. A few aluminium(I) compounds exist: AlF, AlCl, AlBr, and AlI exist in the gaseous phase when the respective trihalide is heated with aluminium, and at cryogenic temperatures. A stable derivative of aluminium monoiodide is the cyclic adduct formed with triethylamine, ... | Aluminium | Wikipedia | 458 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
The industrially most important aluminium hydride is lithium aluminium hydride (LiAlH4), which is used as a reducing agent in organic chemistry. It can be produced from lithium hydride and aluminium trichloride. The simplest hydride, aluminium hydride or alane, is not as important. It is a polymer with the formula (AlH... | Aluminium | Wikipedia | 382 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
Overall, the Earth is about 1.59% aluminium by mass (seventh in abundance by mass). Aluminium occurs in greater proportion in the Earth's crust than in the universe at large. This is because aluminium easily forms the oxide and becomes bound into rocks and stays in the Earth's crust, while less reactive metals sink to ... | Aluminium | Wikipedia | 426 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
The history of aluminium has been shaped by usage of alum. The first written record of alum, made by Greek historian Herodotus, dates back to the 5th century BCE. The ancients are known to have used alum as a dyeing mordant and for city defense. After the Crusades, alum, an indispensable good in the European fabric ind... | Aluminium | Wikipedia | 374 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
As Wöhler's method could not yield great quantities of aluminium, the metal remained rare; its cost exceeded that of gold. The first industrial production of aluminium was established in 1856 by French chemist Henri Etienne Sainte-Claire Deville and companions. Deville had discovered that aluminium trichloride could be... | Aluminium | Wikipedia | 498 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
Throughout the 20th century, the production of aluminium rose rapidly: while the world production of aluminium in 1900 was 6,800 metric tons, the annual production first exceeded 100,000 metric tons in 1916; 1,000,000 tons in 1941; 10,000,000 tons in 1971. In the 1970s, the increased demand for aluminium made it an exc... | Aluminium | Wikipedia | 470 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
Origins
British chemist Humphry Davy, who performed a number of experiments aimed to isolate the metal, is credited as the person who named the element. The first name proposed for the metal to be isolated from alum was alumium, which Davy suggested in an 1808 article on his electrochemical research, published in Phil... | Aluminium | Wikipedia | 416 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
Ludwig Wilhelm Gilbert had proposed Thonerde-metall, after the German "Thonerde" for alumina, in his Annalen der Physik but that name never caught on at all even in Germany. Joseph W. Richards in 1891 found just one occurrence of argillium in Swedish, from the French "argille" for clay. The French themselves had used... | Aluminium | Wikipedia | 473 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
The production of aluminium starts with the extraction of bauxite rock from the ground. The bauxite is processed and transformed using the Bayer process into alumina, which is then processed using the Hall–Héroult process, resulting in the final aluminium.
Aluminium production is highly energy-consuming, and so the pr... | Aluminium | Wikipedia | 459 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
The conversion of alumina to aluminium is achieved by the Hall–Héroult process. In this energy-intensive process, a solution of alumina in a molten () mixture of cryolite (Na3AlF6) with calcium fluoride is electrolyzed to produce metallic aluminium. The liquid aluminium sinks to the bottom of the solution and is tapped... | Aluminium | Wikipedia | 443 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
Recovery of the metal through recycling has become an important task of the aluminium industry. Recycling was a low-profile activity until the late 1960s, when the growing use of aluminium beverage cans brought it to public awareness. Recycling involves melting the scrap, a process that requires only 5% of the energy u... | Aluminium | Wikipedia | 354 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
The major uses for aluminium are in:
Transportation (automobiles, aircraft, trucks, railway cars, marine vessels, bicycles, spacecraft, etc.). Aluminium is used because of its low density;
Packaging (cans, foil, frame, etc.). Aluminium is used because it is non-toxic (see below), non-adsorptive, and splinter-proof;
... | Aluminium | Wikipedia | 386 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
Several sulfates of aluminium have industrial and commercial application. Aluminium sulfate (in its hydrate form) is produced on the annual scale of several millions of metric tons. About two-thirds is consumed in water treatment. The next major application is in the manufacture of paper. It is also used as a mordant i... | Aluminium | Wikipedia | 463 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
Despite its widespread occurrence in the Earth's crust, aluminium has no known function in biology. At pH 6–9 (relevant for most natural waters), aluminium precipitates out of water as the hydroxide and is hence not available; most elements behaving this way have no biological role or are toxic. Aluminium sulfate has a... | Aluminium | Wikipedia | 461 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
Aluminium increases estrogen-related gene expression in human breast cancer cells cultured in the laboratory. In very high doses, aluminium is associated with altered function of the blood–brain barrier. A small percentage of people have contact allergies to aluminium and experience itchy red rashes, headache, muscle p... | Aluminium | Wikipedia | 512 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
In water, aluminium acts as a toxiс agent on gill-breathing animals such as fish when the water is acidic, in which aluminium may precipitate on gills, which causes loss of plasma- and hemolymph ions leading to osmoregulatory failure. Organic complexes of aluminium may be easily absorbed and interfere with metabolism i... | Aluminium | Wikipedia | 340 | 904 | https://en.wikipedia.org/wiki/Aluminium | Physical sciences | Chemistry | null |
An archipelago ( ), sometimes called an island group or island chain, is a chain, cluster, or collection of islands, or a sea containing a small number of scattered islands. An archipelago may be on a lake, river, or an ocean. The list of archipelagos includes the Canadian Arctic Archipelago, the Stockholm Archipelago,... | Archipelago | Wikipedia | 492 | 911 | https://en.wikipedia.org/wiki/Archipelago | Physical sciences | Oceanic and coastal landforms | null |
Superlatives
The largest archipelago in the world by number of islands is the Archipelago Sea, which is part of Finland. There are approximately 40,000 islands, mostly uninhabited.
The largest archipelagic state in the world by area, and by population, is Indonesia. | Archipelago | Wikipedia | 55 | 911 | https://en.wikipedia.org/wiki/Archipelago | Physical sciences | Oceanic and coastal landforms | null |
An axiom, postulate, or assumption is a statement that is taken to be true, to serve as a premise or starting point for further reasoning and arguments. The word comes from the Ancient Greek word (), meaning 'that which is thought worthy or fit' or 'that which commends itself as evident'.
The precise definition varie... | Axiom | Wikipedia | 394 | 928 | https://en.wikipedia.org/wiki/Axiom | Mathematics | Discrete mathematics | null |
Etymology
The word axiom comes from the Greek word (axíōma), a verbal noun from the verb (axioein), meaning "to deem worthy", but also "to require", which in turn comes from (áxios), meaning "being in balance", and hence "having (the same) value (as)", "worthy", "proper". Among the ancient Greek philosophers and mat... | Axiom | Wikipedia | 448 | 928 | https://en.wikipedia.org/wiki/Axiom | Mathematics | Discrete mathematics | null |
The ancient Greeks considered geometry as just one of several sciences, and held the theorems of geometry on par with scientific facts. As such, they developed and used the logico-deductive method as a means of avoiding error, and for structuring and communicating knowledge. Aristotle's posterior analytics is a definit... | Axiom | Wikipedia | 445 | 928 | https://en.wikipedia.org/wiki/Axiom | Mathematics | Discrete mathematics | null |
Modern development
A lesson learned by mathematics in the last 150 years is that it is useful to strip the meaning away from the mathematical assertions (axioms, postulates, propositions, theorems) and definitions. One must concede the need for primitive notions, or undefined terms or concepts, in any study. Such abstr... | Axiom | Wikipedia | 484 | 928 | https://en.wikipedia.org/wiki/Axiom | Mathematics | Discrete mathematics | null |
In the modern understanding, a set of axioms is any collection of formally stated assertions from which other formally stated assertions follow – by the application of certain well-defined rules. In this view, logic becomes just another formal system. A set of axioms should be consistent; it should be impossible to der... | Axiom | Wikipedia | 419 | 928 | https://en.wikipedia.org/wiki/Axiom | Mathematics | Discrete mathematics | null |
Other sciences
Experimental sciences - as opposed to mathematics and logic - also have general founding assertions from which a deductive reasoning can be built so as to express propositions that predict properties - either still general or much more specialized to a specific experimental context. For instance, Newton'... | Axiom | Wikipedia | 417 | 928 | https://en.wikipedia.org/wiki/Axiom | Mathematics | Discrete mathematics | null |
In quantum physics, two sets of postulates have coexisted for some time, which provide a very nice example of falsification. The 'Copenhagen school' (Niels Bohr, Werner Heisenberg, Max Born) developed an operational approach with a complete mathematical formalism that involves the description of quantum system by vecto... | Axiom | Wikipedia | 426 | 928 | https://en.wikipedia.org/wiki/Axiom | Mathematics | Discrete mathematics | null |
Logical axioms
These are certain formulas in a formal language that are universally valid, that is, formulas that are satisfied by every assignment of values. Usually one takes as logical axioms at least some minimal set of tautologies that is sufficient for proving all tautologies in the language; in the case of pred... | Axiom | Wikipedia | 491 | 928 | https://en.wikipedia.org/wiki/Axiom | Mathematics | Discrete mathematics | null |
Axiom scheme for Universal Instantiation.Given a formula in a first-order language , a variable and a term that is substitutable for in , the below formula is universally valid.
Where the symbol stands for the formula with the term substituted for . (See Substitution of variables.) In informal terms, this examp... | Axiom | Wikipedia | 473 | 928 | https://en.wikipedia.org/wiki/Axiom | Mathematics | Discrete mathematics | null |
Examples
This section gives examples of mathematical theories that are developed entirely from a set of non-logical axioms (axioms, henceforth). A rigorous treatment of any of these topics begins with a specification of these axioms.
Basic theories, such as arithmetic, real analysis and complex analysis are often intr... | Axiom | Wikipedia | 390 | 928 | https://en.wikipedia.org/wiki/Axiom | Mathematics | Discrete mathematics | null |
Euclidean geometry
Probably the oldest, and most famous, list of axioms are the 4 + 1 Euclid's postulates of plane geometry. The axioms are referred to as "4 + 1" because for nearly two millennia the fifth (parallel) postulate ("through a point outside a line there is exactly one parallel") was suspected of being deriv... | Axiom | Wikipedia | 417 | 928 | https://en.wikipedia.org/wiki/Axiom | Mathematics | Discrete mathematics | null |
that is, for any statement that is a logical consequence of there actually exists a deduction of the statement from . This is sometimes expressed as "everything that is true is provable", but it must be understood that "true" here means "made true by the set of axioms", and not, for example, "true in the intended int... | Axiom | Wikipedia | 364 | 928 | https://en.wikipedia.org/wiki/Axiom | Mathematics | Discrete mathematics | null |
Asteraceae () is a large family of flowering plants that consists of over 32,000 known species in over 1,900 genera within the order Asterales. The number of species in Asteraceae is rivaled only by the Orchidaceae, and which is the larger family is unclear as the quantity of extant species in each family is unknown. T... | Asteraceae | Wikipedia | 495 | 956 | https://en.wikipedia.org/wiki/Asteraceae | Biology and health sciences | Asterales | null |
Stems
The stems are herbaceous, aerial, branched, and cylindrical with glandular hairs, usually erect, but can be prostrate to ascending. The stems can contain secretory canals with resin, or latex, which is particularly common among the Cichorioideae.
Leaves
Leaves can be alternate, opposite, or whorled. They may be ... | Asteraceae | Wikipedia | 427 | 956 | https://en.wikipedia.org/wiki/Asteraceae | Biology and health sciences | Asterales | null |
The "petals" or "sunrays" in an "asteraceous" head are in fact individual strap-shaped flowers called ray flowers or ray florets, and the "sun disk" is made up of smaller, radially symmetric, individual flowers called disc flowers or disc florets. The word aster means "star" in Greek, referring to the appearance of mos... | Asteraceae | Wikipedia | 502 | 956 | https://en.wikipedia.org/wiki/Asteraceae | Biology and health sciences | Asterales | null |
A ligulate flower is a five-lobed, strap-shaped, individual flower found in the heads of certain other asteraceous species. A ligule is the strap-shaped tongue of the corolla of either a ray flower or of a ligulate flower. A disk flower (or disc flower) is a radially symmetric individual flower in the head, which is ri... | Asteraceae | Wikipedia | 508 | 956 | https://en.wikipedia.org/wiki/Asteraceae | Biology and health sciences | Asterales | null |
Each floret may be subtended by a bract, called a "palea" or "receptacular bract". These bracts are often called "chaff". The presence or absence of these bracts, their distribution on the receptacle, and their size and shape are all important diagnostic characteristics for genera and tribes.
The florets have five pet... | Asteraceae | Wikipedia | 441 | 956 | https://en.wikipedia.org/wiki/Asteraceae | Biology and health sciences | Asterales | null |
There are usually four or five stamens. The filaments are fused to the corolla, while the anthers are generally connate (syngenesious anthers), thus forming a sort of tube around the style (theca). They commonly have basal and/or apical appendages. Pollen is released inside the tube and is collected around the growing ... | Asteraceae | Wikipedia | 484 | 956 | https://en.wikipedia.org/wiki/Asteraceae | Biology and health sciences | Asterales | null |
History
Compositae, the original name for Asteraceae, were first described in 1740 by Dutch botanist Adriaan van Royen. Traditionally, two subfamilies were recognised: Asteroideae (or Tubuliflorae) and Cichorioideae (or Liguliflorae). The latter has been shown to be extensively paraphyletic, and has now been divided in... | Asteraceae | Wikipedia | 453 | 956 | https://en.wikipedia.org/wiki/Asteraceae | Biology and health sciences | Asterales | null |
It is not known whether the precise cause of their great success was the development of the highly specialised capitulum, their ability to store energy as fructans (mainly inulin), which is an advantage in relatively dry zones, or some combination of these and possibly other factors. Heterocarpy, or the ability to prod... | Asteraceae | Wikipedia | 484 | 956 | https://en.wikipedia.org/wiki/Asteraceae | Biology and health sciences | Asterales | null |
Seeds are ordinarily dispersed intact with the fruiting body, the cypsela. Anemochory (wind dispersal) is common, assisted by a hairy pappus. Epizoochory is another common method, in which the dispersal unit, a single cypsela (e.g. Bidens) or entire capitulum (e.g. Arctium) has hooks, spines or some structure to attach... | Asteraceae | Wikipedia | 448 | 956 | https://en.wikipedia.org/wiki/Asteraceae | Biology and health sciences | Asterales | null |
Plants are used as herbs and in herbal teas and other beverages. Chamomile, for example, comes from two different species: the annual Matricaria chamomilla (German chamomile) and the perennial Chamaemelum nobile (Roman chamomile). Calendula (known as pot marigold) is grown commercially for herbal teas and potpourri. Ec... | Asteraceae | Wikipedia | 506 | 956 | https://en.wikipedia.org/wiki/Asteraceae | Biology and health sciences | Asterales | null |
Apiaceae () or Umbelliferae is a family of mostly aromatic flowering plants named after the type genus Apium, and commonly known as the celery, carrot or parsley family, or simply as umbellifers. It is the 16th-largest family of flowering plants, with more than 3,800 species in about 446 genera, including such well-kno... | Apiaceae | Wikipedia | 380 | 957 | https://en.wikipedia.org/wiki/Apiaceae | Biology and health sciences | Apiales | null |
The defining characteristic of this family is the inflorescence, the flowers nearly always aggregated in terminal umbels, that may be simple or more commonly compound, often umbelliform cymes. The flowers are usually perfect (hermaphroditic), and actinomorphic, but there may be zygomorphic flowers at the edge of the um... | Apiaceae | Wikipedia | 206 | 957 | https://en.wikipedia.org/wiki/Apiaceae | Biology and health sciences | Apiales | null |
There is often variation in the functionality of the stamens even within a single inflorescence. Some flowers are functionally staminate (where a pistil may be present but has no ovules capable of being fertilized) while others are functionally pistillate (where stamens are present but their anthers do not produce viab... | Apiaceae | Wikipedia | 312 | 957 | https://en.wikipedia.org/wiki/Apiaceae | Biology and health sciences | Apiales | null |
Taxonomy
Apiaceae was first described by John Lindley in 1836. The name is derived from the type genus Apium, which was originally used by Pliny the Elder circa 50 AD for a celery-like plant. The alternative name for the family, Umbelliferae, derives from the inflorescence being generally in the form of a compound umb... | Apiaceae | Wikipedia | 412 | 957 | https://en.wikipedia.org/wiki/Apiaceae | Biology and health sciences | Apiales | null |
The Platysace clade and the genera Klotzschia and Hermas fell outside the four subfamilies. It was suggested that they could be accommodated in subfamilies of their own. Phlyctidocarpa was formerly placed in the subfamily Apioideae, but if kept there makes Apioideae paraphyletic. It could be placed in an enlarged Sanic... | Apiaceae | Wikipedia | 456 | 957 | https://en.wikipedia.org/wiki/Apiaceae | Biology and health sciences | Apiales | null |
Other notable cultivated Apiaceae include chervil (Anthriscus cerefolium), angelica (Angelica spp.), celery (Apium graveolens), arracacha (Arracacia xanthorrhiza), sea holly (Eryngium spp.), asafoetida (Ferula asafoetida), galbanum (Ferula gummosa), cicely (Myrrhis odorata), anise (Pimpinella anisum), lovage (Levisticu... | Apiaceae | Wikipedia | 390 | 957 | https://en.wikipedia.org/wiki/Apiaceae | Biology and health sciences | Apiales | null |
Toxicity
Many species in the family Apiaceae produce phototoxic substances (called furanocoumarins) that sensitize human skin to sunlight. Contact with plant parts that contain furanocoumarins, followed by exposure to sunlight, may cause phytophotodermatitis, a serious skin inflammation. Phototoxic species include Amm... | Apiaceae | Wikipedia | 238 | 957 | https://en.wikipedia.org/wiki/Apiaceae | Biology and health sciences | Apiales | null |
An axon (from Greek ἄξων áxōn, axis) or nerve fiber (or nerve fibre: see spelling differences) is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action potentials away from the nerve cell body. The function of the axon is to transmit informati... | Axon | Wikipedia | 424 | 958 | https://en.wikipedia.org/wiki/Axon | Biology and health sciences | Nervous system | Biology |
Axons are covered by a membrane known as an axolemma; the cytoplasm of an axon is called axoplasm. Most axons branch, in some cases very profusely. The end branches of an axon are called telodendria. The swollen end of a telodendron is known as the axon terminal or end-foot which joins the dendrite or cell body of anot... | Axon | Wikipedia | 345 | 958 | https://en.wikipedia.org/wiki/Axon | Biology and health sciences | Nervous system | Biology |
Axons are the primary transmission lines of the nervous system, and as bundles they form nerves in the peripheral nervous system, or nerve tracts in the central nervous system (CNS). Some axons can extend up to one meter or more while others extend as little as one millimeter. The longest axons in the human body are th... | Axon | Wikipedia | 417 | 958 | https://en.wikipedia.org/wiki/Axon | Biology and health sciences | Nervous system | Biology |
The myelinated axons from the cortical neurons form the bulk of the neural tissue called white matter in the brain. The myelin gives the white appearance to the tissue in contrast to the grey matter of the cerebral cortex which contains the neuronal cell bodies. A similar arrangement is seen in the cerebellum. Bundles ... | Axon | Wikipedia | 487 | 958 | https://en.wikipedia.org/wiki/Axon | Biology and health sciences | Nervous system | Biology |
The axon initial segment is unmyelinated and contains a specialized complex of proteins. It is between approximately 20 and 60 μm in length and functions as the site of action potential initiation. Both the position on the axon and the length of the AIS can change showing a degree of plasticity that can fine-tune the n... | Axon | Wikipedia | 405 | 958 | https://en.wikipedia.org/wiki/Axon | Biology and health sciences | Nervous system | Biology |
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