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Gödel's completeness theorem for first-order logic: every consistent set of first-order sentences has a completion. That is, every consistent set of first-order sentences can be extended to a maximal consistent set.
The compactness theorem: If is a set of first-order (or alternatively, zero-order) sentences such that ... | Axiom of choice | Wikipedia | 82 | 840 | https://en.wikipedia.org/wiki/Axiom%20of%20choice | Mathematics | Discrete mathematics | null |
Possibly equivalent implications of AC
There are several historically important set-theoretic statements implied by AC whose equivalence to AC is open. Zermelo cited the partition principle, which was formulated before AC itself, as a justification for believing AC. In 1906, Russell declared PP to be equivalent, but wh... | Axiom of choice | Wikipedia | 451 | 840 | https://en.wikipedia.org/wiki/Axiom%20of%20choice | Mathematics | Discrete mathematics | null |
It is also consistent with ZF + DC that every set of reals is Lebesgue measurable, but this consistency result, due to Robert M. Solovay, cannot be proved in ZFC itself, but requires a mild large cardinal assumption (the existence of an inaccessible cardinal). The much stronger axiom of determinacy, or AD, implies that... | Axiom of choice | Wikipedia | 337 | 840 | https://en.wikipedia.org/wiki/Axiom%20of%20choice | Mathematics | Discrete mathematics | null |
The negation of the weak partition principle: There is a set that can be partitioned into strictly more equivalence classes than the original set has elements, and a function whose domain is strictly smaller than its range. In fact, this is the case in all known models.
There is a function f from the real numbers to th... | Axiom of choice | Wikipedia | 408 | 840 | https://en.wikipedia.org/wiki/Axiom%20of%20choice | Mathematics | Discrete mathematics | null |
In type theory, a different kind of statement is known as the axiom of choice. This form begins with two types, σ and τ, and a relation R between objects of type σ and objects of type τ. The axiom of choice states that if for each x of type σ there exists a y of type τ such that R(x,y), then there is a function f from ... | Axiom of choice | Wikipedia | 148 | 840 | https://en.wikipedia.org/wiki/Axiom%20of%20choice | Mathematics | Discrete mathematics | null |
An aircraft (: aircraft) is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or the dynamic lift of an airfoil, or, in a few cases, direct downward thrust from its engines. Common examples of aircraft include airplanes, rotorcraft, helicopters, ... | Aircraft | Wikipedia | 507 | 849 | https://en.wikipedia.org/wiki/Aircraft | Technology | Transportation | null |
A balloon was originally any aerostat, while the term airship was used for large, powered aircraft designs — usually fixed-wing. In 1919, Frederick Handley Page was reported as referring to "ships of the air," with smaller passenger types as "Air yachts." In the 1930s, large intercontinental flying boats were also some... | Aircraft | Wikipedia | 502 | 849 | https://en.wikipedia.org/wiki/Aircraft | Technology | Transportation | null |
Aerodynamic lift involving wings is the most common, and can be achieved via two methods. Fixed-wing aircraft (airplanes and gliders) achieve airflow past the wings by having the entire aircraft moving forward through the air, while rotorcraft (helicopters and autogyros) do so by having mobile, elongated wings spinning... | Aircraft | Wikipedia | 467 | 849 | https://en.wikipedia.org/wiki/Aircraft | Technology | Transportation | null |
Besides the method of propulsion (if any), fixed-wing aircraft are in general characterized by their wing configuration. The most important wing characteristics are:
Number of wings – Monoplane, biplane, triplane, or multiplane.
Wing support – Braced or cantilever, rigid or flexible.
Wing planform – including aspect... | Aircraft | Wikipedia | 490 | 849 | https://en.wikipedia.org/wiki/Aircraft | Technology | Transportation | null |
Compound rotorcraft have wings that provide some or all of the lift in forward flight. They are nowadays classified as powered lift types and not as rotorcraft. Tiltrotor aircraft (such as the Bell Boeing V-22 Osprey), tiltwing, tail-sitter, and coleopter aircraft have their rotors/propellers horizontal for vertical fl... | Aircraft | Wikipedia | 463 | 849 | https://en.wikipedia.org/wiki/Aircraft | Technology | Transportation | null |
The largest aircraft by weight and largest regular fixed-wing aircraft ever built, , was the Antonov An-225 Mriya. That Soviet-built (Ukrainian SSR) six-engine transport of the 1980s was long, with an wingspan. It holds the world payload record, after transporting of goods, and has flown loads commercially. With a ... | Aircraft | Wikipedia | 484 | 849 | https://en.wikipedia.org/wiki/Aircraft | Technology | Transportation | null |
The fastest manned, air-breathing powered airplane is the Lockheed SR-71 Blackbird, a U.S. reconnaissance jet fixed-wing aircraft, having reached on 28 July 1976.
Propulsion
Unpowered aircraft
Gliders are heavier-than-air aircraft that do not employ propulsion once airborne. Take-off may be by launching forward an... | Aircraft | Wikipedia | 496 | 849 | https://en.wikipedia.org/wiki/Aircraft | Technology | Transportation | null |
Many kinds of power plant have been used to drive propellers. Early airships used man power or steam engines. The more practical internal combustion piston engine was used for virtually all fixed-wing aircraft until World War II and is still used in many smaller aircraft. Some types use turbine engines to drive a prope... | Aircraft | Wikipedia | 512 | 849 | https://en.wikipedia.org/wiki/Aircraft | Technology | Transportation | null |
Design and construction
Aircraft are designed according to many factors such as customer and manufacturer demand, safety protocols and physical and economic constraints. For many types of aircraft the design process is regulated by national airworthiness authorities.
The key parts of an aircraft are generally divided... | Aircraft | Wikipedia | 452 | 849 | https://en.wikipedia.org/wiki/Aircraft | Technology | Transportation | null |
The source of motive power for an aircraft is normally called the powerplant, and includes engine or motor, propeller or rotor, (if any), jet nozzles and thrust reversers (if any), and accessories essential to the functioning of the engine or motor (e.g.: starter, ignition system, intake system, exhaust system, fuel sy... | Aircraft | Wikipedia | 452 | 849 | https://en.wikipedia.org/wiki/Aircraft | Technology | Transportation | null |
Flight dynamics is the science of air vehicle orientation and control in three dimensions. The three critical flight dynamics parameters are the angles of rotation around three axes which pass through the vehicle's center of gravity, known as pitch, roll, and yaw.
Roll is a rotation about the longitudinal axis (equiva... | Aircraft | Wikipedia | 480 | 849 | https://en.wikipedia.org/wiki/Aircraft | Technology | Transportation | null |
Aerospace engineers develop control systems for a vehicle's orientation (attitude) about its center of mass. The control systems include actuators, which exert forces in various directions, and generate rotational forces or moments about the aerodynamic center of the aircraft, and thus rotate the aircraft in pitch, rol... | Aircraft | Wikipedia | 487 | 849 | https://en.wikipedia.org/wiki/Aircraft | Technology | Transportation | null |
Commercial aircraft include types designed for scheduled and charter airline flights, carrying passengers, mail and other cargo. The larger passenger-carrying types are the airliners, the largest of which are wide-body aircraft. Some of the smaller types are also used in general aviation, and some of the larger types a... | Aircraft | Wikipedia | 253 | 849 | https://en.wikipedia.org/wiki/Aircraft | Technology | Transportation | null |
Argon is a chemical element; it has symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abundant as water vapor (which averages about 4000 ppmv, but varies greatly), 23 tim... | Argon | Wikipedia | 476 | 896 | https://en.wikipedia.org/wiki/Argon | Physical sciences | Chemical elements_2 | null |
Although argon is a noble gas, it can form some compounds under various extreme conditions. Argon fluorohydride (HArF), a compound of argon with fluorine and hydrogen that is stable below , has been demonstrated. Although the neutral ground-state chemical compounds of argon are presently limited to HArF, argon can form... | Argon | Wikipedia | 451 | 896 | https://en.wikipedia.org/wiki/Argon | Physical sciences | Chemical elements_2 | null |
Before isolating the gas, they had determined that nitrogen produced from chemical compounds was 0.5% lighter than nitrogen from the atmosphere. The difference was slight, but it was important enough to attract their attention for many months. They concluded that there was another gas in the air mixed in with the nitro... | Argon | Wikipedia | 423 | 896 | https://en.wikipedia.org/wiki/Argon | Physical sciences | Chemical elements_2 | null |
Between locations in the Solar System, the isotopic composition of argon varies greatly. Where the major source of argon is the decay of in rocks, will be the dominant isotope, as it is on Earth. Argon produced directly by stellar nucleosynthesis is dominated by the alpha-process nuclide . Correspondingly, solar argo... | Argon | Wikipedia | 316 | 896 | https://en.wikipedia.org/wiki/Argon | Physical sciences | Chemical elements_2 | null |
Argon's complete octet of electrons indicates full s and p subshells. This full valence shell makes argon very stable and extremely resistant to bonding with other elements. Before 1962, argon and the other noble gases were considered to be chemically inert and unable to form compounds; however, compounds of the heavie... | Argon | Wikipedia | 497 | 896 | https://en.wikipedia.org/wiki/Argon | Physical sciences | Chemical elements_2 | null |
Other noble gases would be equally suitable for most of these applications, but argon is by far the cheapest. It is inexpensive, since it occurs naturally in air and is readily obtained as a byproduct of cryogenic air separation in the production of liquid oxygen and liquid nitrogen: the primary constituents of air are... | Argon | Wikipedia | 349 | 896 | https://en.wikipedia.org/wiki/Argon | Physical sciences | Chemical elements_2 | null |
Scientific research
Liquid argon is used as the target for neutrino experiments and direct dark matter searches. The interaction between the hypothetical WIMPs and an argon nucleus produces scintillation light that is detected by photomultiplier tubes. Two-phase detectors containing argon gas are used to detect the ion... | Argon | Wikipedia | 488 | 896 | https://en.wikipedia.org/wiki/Argon | Physical sciences | Chemical elements_2 | null |
In winemaking, argon is used in a variety of activities to provide a barrier against oxygen at the liquid surface, which can spoil wine by fueling both microbial metabolism (as with acetic acid bacteria) and standard redox chemistry.
Argon is sometimes used as the propellant in aerosol cans.
Argon is also used as a p... | Argon | Wikipedia | 444 | 896 | https://en.wikipedia.org/wiki/Argon | Physical sciences | Chemical elements_2 | null |
Incandescent lights are filled with argon, to preserve the filaments at high temperature from oxidation. It is used for the specific way it ionizes and emits light, such as in plasma globes and calorimetry in experimental particle physics. Gas-discharge lamps filled with pure argon provide lilac/violet light; with argo... | Argon | Wikipedia | 429 | 896 | https://en.wikipedia.org/wiki/Argon | Physical sciences | Chemical elements_2 | null |
Arsenic is a chemical element with the symbol As and the atomic number 33. It is a metalloid and one of the pnictogens, and therefore shares many properties with its group 15 neighbors phosphorus and antimony. Arsenic is a notoriously toxic heavy metal. It occurs naturally in many minerals, usually in combination with ... | Arsenic | Wikipedia | 376 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
The three most common arsenic allotropes are grey, yellow, and black arsenic, with grey being the most common. Grey arsenic (α-As, space group Rm No. 166) adopts a double-layered structure consisting of many interlocked, ruffled, six-membered rings. Because of weak bonding between the layers, grey arsenic is brittle an... | Arsenic | Wikipedia | 386 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
Arsenic occurs in nature as one stable isotope, 75As, and is therefore called a monoisotopic element. As of 2024, at least 32 radioisotopes have also been synthesized, ranging in atomic mass from 64 to 95. The most stable of these is 73As with a half-life of 80.30 days. All other isotopes have half-lives of under one d... | Arsenic | Wikipedia | 232 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
Arsenic has a similar electronegativity and ionization energies to its lighter pnictogen congener phosphorus and therefore readily forms covalent molecules with most of the nonmetals. Though stable in dry air, arsenic forms a golden-bronze tarnish upon exposure to humidity which eventually becomes a black surface layer... | Arsenic | Wikipedia | 439 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
One of the simplest arsenic compounds is the trihydride, the highly toxic, flammable, pyrophoric arsine (AsH3). This compound is generally regarded as stable, since at room temperature it decomposes only slowly. At temperatures of 250–300 °C decomposition to arsenic and hydrogen is rapid. Several factors, such as humid... | Arsenic | Wikipedia | 444 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
All trihalides of arsenic(III) are well known except the astatide, which is unknown. Arsenic pentafluoride (AsF5) is the only important pentahalide, reflecting the lower stability of the +5 oxidation state; even so, it is a very strong fluorinating and oxidizing agent. (The pentachloride is stable only below −50 °C, at... | Arsenic | Wikipedia | 509 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
In 2014, China was the top producer of white arsenic with almost 70% world share, followed by Morocco, Russia, and Belgium, according to the British Geological Survey and the United States Geological Survey. Most arsenic refinement operations in the US and Europe have closed over environmental concerns. Arsenic is foun... | Arsenic | Wikipedia | 465 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
During the Bronze Age, arsenic was melted with copper to make arsenical bronze.
Jabir ibn Hayyan described the isolation of arsenic before 815 AD. Albertus Magnus (Albert the Great, 1193–1280) later isolated the element from a compound in 1250, by heating soap together with arsenic trisulfide. In 1649, Johann Schröder ... | Arsenic | Wikipedia | 445 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
In small doses, soluble arsenic compounds act as stimulants, and were once popular as medicine by people in the mid-18th to 19th centuries; this use was especially prevalent for sport animals such as race horses or work dogs and continued into the 20th century.
A 2006 study of the remains of the Australian racehorse P... | Arsenic | Wikipedia | 482 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
Arsenic is used as a feed additive in poultry and swine production, in particular it was used in the U.S. until 2015 to increase weight gain, improve feed efficiency, and prevent disease. An example is roxarsone, which had been used as a broiler starter by about 70% of U.S. broiler growers. In 2011, Alpharma, a subsidi... | Arsenic | Wikipedia | 390 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
The main use of arsenic is in alloying with lead. Lead components in car batteries are strengthened by the presence of a very small percentage of arsenic. Dezincification of brass (a copper-zinc alloy) is greatly reduced by the addition of arsenic. "Phosphorus Deoxidized Arsenical Copper" with an arsenic content of 0.3... | Arsenic | Wikipedia | 462 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
Bacteria
Some species of bacteria obtain their energy in the absence of oxygen by oxidizing various fuels while reducing arsenate to arsenite. Under oxidative environmental conditions some bacteria use arsenite as fuel, which they oxidize to arsenate. The enzymes involved are known as arsenate reductases (Arr).
In 20... | Arsenic | Wikipedia | 509 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
The Chinese brake fern (Pteris vittata) hyperaccumulates arsenic from the soil into its leaves and has a proposed use in phytoremediation.
Biomethylation
Inorganic arsenic and its compounds, upon entering the food chain, are progressively metabolized through a process of methylation. For example, the mold Scopulario... | Arsenic | Wikipedia | 324 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
Extensive arsenic contamination of groundwater has led to widespread arsenic poisoning in Bangladesh and neighboring countries. It is estimated that approximately 57 million people in the Bengal basin are drinking groundwater with arsenic concentrations elevated above the World Health Organization's standard of 10 part... | Arsenic | Wikipedia | 443 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
In the United States, arsenic is most commonly found in the ground waters of the southwest. Parts of New England, Michigan, Wisconsin, Minnesota and the Dakotas are also known to have significant concentrations of arsenic in ground water. Increased levels of skin cancer have been associated with arsenic exposure in Wis... | Arsenic | Wikipedia | 491 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
Early (1973) evaluations of the processes for removing dissolved arsenic from drinking water demonstrated the efficacy of co-precipitation with either iron or aluminium oxides. In particular, iron as a coagulant was found to remove arsenic with an efficacy exceeding 90%. Several adsorptive media systems have been appro... | Arsenic | Wikipedia | 487 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
Hazard maps for contaminated groundwater
Around one-third of the world's population drinks water from groundwater resources. Of this, about 10 percent, approximately 300 million people, obtains water from groundwater resources that are contaminated with unhealthy levels of arsenic or fluoride. These trace elements der... | Arsenic | Wikipedia | 429 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
Oxidation and reduction affects the migration of arsenic in subsurface environments. Arsenite is the most stable soluble form of arsenic in reducing environments and arsenate, which is less mobile than arsenite, is dominant in oxidizing environments at neutral pH. Therefore, arsenic may be more mobile under reducing co... | Arsenic | Wikipedia | 347 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
Some species of bacteria catalyze redox transformations of arsenic. Dissimilatory arsenate-respiring prokaryotes (DARP) speed up the reduction of As(V) to As(III). DARP use As(V) as the electron acceptor of anaerobic respiration and obtain energy to survive. Other organic and inorganic substances can be oxidized in thi... | Arsenic | Wikipedia | 432 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
Wood preservation in the US
As of 2002, US-based industries consumed 19,600 metric tons of arsenic. Ninety percent of this was used for treatment of wood with chromated copper arsenate (CCA). In 2007, 50% of the 5,280 metric tons of consumption was still used for this purpose. In the United States, the voluntary phasi... | Arsenic | Wikipedia | 497 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
Physical, chemical, and biological methods have been used to remediate arsenic contaminated water. Bioremediation is said to be cost-effective and environmentally friendly. Bioremediation of ground water contaminated with arsenic aims to convert arsenite, the toxic form of arsenic to humans, to arsenate. Arsenate (+5 o... | Arsenic | Wikipedia | 470 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
Arsenic and many of its compounds are especially potent poisons (e.g. arsine). Small amount of arsenic can be detected by pharmacopoial methods which includes reduction of arsenic to arsenious with help of zinc and can be confirmed with mercuric chloride paper.
Classification
Elemental arsenic and arsenic sulfate an... | Arsenic | Wikipedia | 399 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
In 2008, based on its ongoing testing of a wide variety of American foods for toxic chemicals, the U.S. Food and Drug Administration set the "level of concern" for inorganic arsenic in apple and pear juices at 23 ppb, based on non-carcinogenic effects, and began blocking importation of products in excess of this level;... | Arsenic | Wikipedia | 431 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
Consumer Reports recommended:
That the EPA and FDA eliminate arsenic-containing fertilizer, drugs, and pesticides in food production;
That the FDA establish a legal limit for food;
That industry change production practices to lower arsenic levels, especially in food for children; and
That consumers test home water ... | Arsenic | Wikipedia | 402 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
Arsenic disrupts ATP production through several mechanisms. At the level of the citric acid cycle, arsenic inhibits lipoic acid, which is a cofactor for pyruvate dehydrogenase. By competing with phosphate, arsenate uncouples oxidative phosphorylation, thus inhibiting energy-linked reduction of NAD+, mitochondrial respi... | Arsenic | Wikipedia | 499 | 897 | https://en.wikipedia.org/wiki/Arsenic | Physical sciences | Chemical elements_2 | null |
Antimony is a chemical element; it has symbol Sb () and atomic number 51. A lustrous grey metal or metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient times and were powdered for use as medicine and cosmetics, often known by the Arabic name k... | Antimony | Wikipedia | 409 | 898 | https://en.wikipedia.org/wiki/Antimony | Physical sciences | Chemical elements_2 | null |
The only stable allotrope of antimony under standard conditions is metallic, brittle, silver-white, and shiny. It crystallises in a trigonal cell, isomorphic with bismuth and the gray allotrope of arsenic, and is formed when molten antimony is cooled slowly. Amorphous black antimony is formed upon rapid cooling of anti... | Antimony | Wikipedia | 383 | 898 | https://en.wikipedia.org/wiki/Antimony | Physical sciences | Chemical elements_2 | null |
Antimony has two stable isotopes: 121Sb with a natural abundance of 57.36% and 123Sb with a natural abundance of 42.64%. It also has 35 radioisotopes, of which the longest-lived is 125Sb with a half-life of 2.75 years. In addition, 29 metastable states have been characterized. The most stable of these is 120m1Sb with a... | Antimony | Wikipedia | 440 | 898 | https://en.wikipedia.org/wiki/Antimony | Physical sciences | Chemical elements_2 | null |
Antimonous acid is unknown, but the conjugate base sodium antimonite () forms upon fusing sodium oxide and . Transition metal antimonites are also known. Antimonic acid exists only as the hydrate , forming salts as the antimonate anion . When a solution containing this anion is dehydrated, the precipitate contains mix... | Antimony | Wikipedia | 403 | 898 | https://en.wikipedia.org/wiki/Antimony | Physical sciences | Chemical elements_2 | null |
Antimonides, hydrides, and organoantimony compounds
Compounds in this class generally are described as derivatives of Sb3−. Antimony forms antimonides with metals, such as indium antimonide (InSb) and silver antimonide (). The alkali metal and zinc antimonides, such as Na3Sb and Zn3Sb2, are more reactive. Treating thes... | Antimony | Wikipedia | 442 | 898 | https://en.wikipedia.org/wiki/Antimony | Physical sciences | Chemical elements_2 | null |
The British archaeologist Roger Moorey was unconvinced the artifact was indeed a vase, mentioning that Selimkhanov, after his analysis of the Tello object (published in 1975), "attempted to relate the metal to Transcaucasian natural antimony" (i.e. native metal) and that "the antimony objects from Transcaucasia are all... | Antimony | Wikipedia | 486 | 898 | https://en.wikipedia.org/wiki/Antimony | Physical sciences | Chemical elements_2 | null |
The first discovery of naturally occurring pure antimony in the Earth's crust was described by the Swedish scientist and local mine district engineer Anton von Swab in 1783; the type-sample was collected from the Sala Silver Mine in the Bergslagen mining district of Sala, Västmanland, Sweden.
Etymology
The medieval La... | Antimony | Wikipedia | 433 | 898 | https://en.wikipedia.org/wiki/Antimony | Physical sciences | Chemical elements_2 | null |
The Arabic word for the substance, as opposed to the cosmetic, can appear as ithmid, athmoud, othmod, or uthmod. Littré suggests the first form, which is the earliest, derives from stimmida, an accusative for stimmi. The Greek word στίμμι (stimmi) is used by Attic tragic poets of the 5th century BC, and is possibly a ... | Antimony | Wikipedia | 489 | 898 | https://en.wikipedia.org/wiki/Antimony | Physical sciences | Chemical elements_2 | null |
Supply risk
For antimony-importing regions, such as Europe and the U.S., antimony is considered to be a critical mineral for industrial manufacturing that is at risk of supply chain disruption. With global production coming mainly from China (74%), Tajikistan (8%), and Russia (4%), these sources are critical to supply.... | Antimony | Wikipedia | 378 | 898 | https://en.wikipedia.org/wiki/Antimony | Physical sciences | Chemical elements_2 | null |
Antimony forms a highly useful alloy with lead, increasing its hardness and mechanical strength. When casting it increases fluidity of the melt and reduces shrinkage during cooling. For most applications involving lead, varying amounts of antimony are used as alloying metal. In lead–acid batteries, this addition improv... | Antimony | Wikipedia | 401 | 898 | https://en.wikipedia.org/wiki/Antimony | Physical sciences | Chemical elements_2 | null |
Biology and medicine have few uses for antimony. Treatments containing antimony, known as antimonials, are used as emetics. Antimony compounds are used as antiprotozoan drugs. Potassium antimonyl tartrate, or tartar emetic, was once used as an anti-schistosomal drug from 1919 on. It was subsequently replaced by praziqu... | Antimony | Wikipedia | 463 | 898 | https://en.wikipedia.org/wiki/Antimony | Physical sciences | Chemical elements_2 | null |
Antimony and many of its compounds are toxic, and the effects of antimony poisoning are similar to arsenic poisoning. The toxicity of antimony is far lower than that of arsenic; this might be caused by the significant differences of uptake, metabolism and excretion between arsenic and antimony. The uptake of antimony(I... | Antimony | Wikipedia | 493 | 898 | https://en.wikipedia.org/wiki/Antimony | Physical sciences | Chemical elements_2 | null |
The tolerable daily intake (TDI) proposed by WHO is 6 μg antimony per kilogram of body weight. The immediately dangerous to life or health (IDLH) value for antimony is 50 mg/m3.
Toxicity
Certain compounds of antimony appear to be toxic, particularly antimony trioxide and antimony potassium tartrate. Effects may be s... | Antimony | Wikipedia | 211 | 898 | https://en.wikipedia.org/wiki/Antimony | Physical sciences | Chemical elements_2 | null |
Actinium is a chemical element; it has symbol Ac and atomic number 89. It was first isolated by Friedrich Oskar Giesel in 1902, who gave it the name emanium; the element got its name by being wrongly identified with a substance André-Louis Debierne found in 1899 and called actinium. The actinide series, a set of 15 ele... | Actinium | Wikipedia | 374 | 899 | https://en.wikipedia.org/wiki/Actinium | Physical sciences | Chemical elements_2 | null |
History
André-Louis Debierne, a French chemist, announced the discovery of a new element in 1899. He separated it from pitchblende residues left by Marie and Pierre Curie after they had extracted radium. In 1899, Debierne described the substance as similar to titanium and (in 1900) as similar to thorium. Friedrich Oska... | Actinium | Wikipedia | 503 | 899 | https://en.wikipedia.org/wiki/Actinium | Physical sciences | Chemical elements_2 | null |
Properties
Actinium is a soft, silvery-white, radioactive, metallic element. Its estimated shear modulus is similar to that of lead. Owing to its strong radioactivity, actinium glows in the dark with a pale blue light, which originates from the surrounding air ionized by the emitted energetic particles. Actinium has si... | Actinium | Wikipedia | 409 | 899 | https://en.wikipedia.org/wiki/Actinium | Physical sciences | Chemical elements_2 | null |
Due to actinium's intense radioactivity, only a limited number of actinium compounds are known. These include: AcF3, AcCl3, AcBr3, AcOF, AcOCl, AcOBr, Ac2S3, Ac2O3, AcPO4 and Ac(NO3)3. They all contain actinium in the oxidation state +3. In particular, the lattice constants of the analogous lanthanum and actinium compo... | Actinium | Wikipedia | 499 | 899 | https://en.wikipedia.org/wiki/Actinium | Physical sciences | Chemical elements_2 | null |
and treating it with ammonium hydroxide at results in the oxybromide AcOBr.
Other compounds
Actinium hydride was obtained by reduction of actinium trichloride with potassium at , and its structure was deduced by analogy with the corresponding LaH2 hydride. The source of hydrogen in the reaction was uncertain.
Mixing... | Actinium | Wikipedia | 511 | 899 | https://en.wikipedia.org/wiki/Actinium | Physical sciences | Chemical elements_2 | null |
Actinium is found only in traces in uranium ores – one tonne of uranium in ore contains about 0.2 milligrams of 227Ac – and in thorium ores, which contain about 5 nanograms of 228Ac per one tonne of thorium. The actinium isotope 227Ac is a transient member of the uranium-actinium series decay chain, which begins with t... | Actinium | Wikipedia | 217 | 899 | https://en.wikipedia.org/wiki/Actinium | Physical sciences | Chemical elements_2 | null |
The low natural concentration, and the close similarity of physical and chemical properties to those of lanthanum and other lanthanides, which are always abundant in actinium-bearing ores, render separation of actinium from the ore impractical. The most concentrated actinium sample prepared from raw material consisted ... | Actinium | Wikipedia | 478 | 899 | https://en.wikipedia.org/wiki/Actinium | Physical sciences | Chemical elements_2 | null |
Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor in vacuum at a temperature between . Higher temperatures resulted in evaporation of the product and lower ones lead to an incomplete transformation. Lithium was chosen among other alkali metals because its fluoride is most volatil... | Actinium | Wikipedia | 341 | 899 | https://en.wikipedia.org/wiki/Actinium | Physical sciences | Chemical elements_2 | null |
225Ac is applied in medicine to produce in a reusable generator or can be used alone as an agent for radiation therapy, in particular targeted alpha therapy (TAT). This isotope has a half-life of 10 days, making it much more suitable for radiation therapy than 213Bi (half-life 46 minutes). Additionally, 225Ac decays t... | Actinium | Wikipedia | 354 | 899 | https://en.wikipedia.org/wiki/Actinium | Physical sciences | Chemical elements_2 | null |
The medium half-life of 227Ac (21.77 years) makes it a very convenient radioactive isotope in modeling the slow vertical mixing of oceanic waters. The associated processes cannot be studied with the required accuracy by direct measurements of current velocities (of the order 50 meters per year). However, evaluation of ... | Actinium | Wikipedia | 362 | 899 | https://en.wikipedia.org/wiki/Actinium | Physical sciences | Chemical elements_2 | null |
Americium is a synthetic chemical element; it has symbol Am and atomic number 95. It is radioactive and a transuranic member of the actinide series in the periodic table, located under the lanthanide element europium and was thus named after the Americas by analogy.
Americium was first produced in 1944 by the group of... | Americium | Wikipedia | 378 | 900 | https://en.wikipedia.org/wiki/Americium | Physical sciences | Chemical elements_2 | null |
Although americium was likely produced in previous nuclear experiments, it was first intentionally synthesized, isolated and identified in late autumn 1944, at the University of California, Berkeley, by Glenn T. Seaborg, Leon O. Morgan, Ralph A. James, and Albert Ghiorso. They used a 60-inch cyclotron at the University... | Americium | Wikipedia | 508 | 900 | https://en.wikipedia.org/wiki/Americium | Physical sciences | Chemical elements_2 | null |
The times are half-lives
The second isotope 242Am was produced upon neutron bombardment of the already-created 241Am. Upon rapid β-decay, 242Am converts into the isotope of curium 242Cm (which had been discovered previously). The half-life of this decay was initially determined at 17 hours, which was close to the pres... | Americium | Wikipedia | 424 | 900 | https://en.wikipedia.org/wiki/Americium | Physical sciences | Chemical elements_2 | null |
Existing americium is concentrated in the areas used for the atmospheric nuclear weapons tests conducted between 1945 and 1980, as well as at the sites of nuclear incidents, such as the Chernobyl disaster. For example, the analysis of the debris at the testing site of the first U.S. hydrogen bomb, Ivy Mike, (1 November... | Americium | Wikipedia | 480 | 900 | https://en.wikipedia.org/wiki/Americium | Physical sciences | Chemical elements_2 | null |
Americium has been produced in small quantities in nuclear reactors for decades, and kilograms of its 241Am and 243Am isotopes have been accumulated by now. Nevertheless, since it was first offered for sale in 1962, its price, about of 241Am, remains almost unchanged owing to the very complex separation procedure. The... | Americium | Wikipedia | 502 | 900 | https://en.wikipedia.org/wiki/Americium | Physical sciences | Chemical elements_2 | null |
^{239}_{94}Pu ->[\ce{4(n,\gamma)}] \ ^{243}_{94}Pu ->[\beta^-][4.956 \ \ce{h}] ^{243}_{95}Am
Metal generation
Most synthesis routines yield a mixture of different actinide isotopes in oxide forms, from which isotopes of americium can be separated. In a typical procedure, the spent reactor fuel (e.g. MOX fuel) is diss... | Americium | Wikipedia | 477 | 900 | https://en.wikipedia.org/wiki/Americium | Physical sciences | Chemical elements_2 | null |
In the periodic table, americium is located to the right of plutonium, to the left of curium, and below the lanthanide europium, with which it shares many physical and chemical properties. Americium is a highly radioactive element. When freshly prepared, it has a silvery-white metallic lustre, but then slowly tarnishes... | Americium | Wikipedia | 224 | 900 | https://en.wikipedia.org/wiki/Americium | Physical sciences | Chemical elements_2 | null |
At ambient conditions, americium is present in its most stable α form which has a hexagonal crystal symmetry, and a space group P63/mmc with cell parameters a = 346.8 pm and c = 1124 pm, and four atoms per unit cell. The crystal consists of a double-hexagonal close packing with the layer sequence ABAC and so is isotypi... | Americium | Wikipedia | 393 | 900 | https://en.wikipedia.org/wiki/Americium | Physical sciences | Chemical elements_2 | null |
As with many other actinides, self-damage of the crystal structure due to alpha-particle irradiation is intrinsic to americium. It is especially noticeable at low temperatures, where the mobility of the produced structure defects is relatively low, by broadening of X-ray diffraction peaks. This effect makes somewhat un... | Americium | Wikipedia | 435 | 900 | https://en.wikipedia.org/wiki/Americium | Physical sciences | Chemical elements_2 | null |
Chemical properties
Americium metal readily reacts with oxygen and dissolves in aqueous acids. The most stable oxidation state for americium is +3. The chemistry of americium(III) has many similarities to the chemistry of lanthanide(III) compounds. For example, trivalent americium forms insoluble fluoride, oxalate, iod... | Americium | Wikipedia | 479 | 900 | https://en.wikipedia.org/wiki/Americium | Physical sciences | Chemical elements_2 | null |
Oxygen compounds
Three americium oxides are known, with the oxidation states +2 (AmO), +3 (Am2O3) and +4 (AmO2). Americium(II) oxide was prepared in minute amounts and has not been characterized in detail. Americium(III) oxide is a red-brown solid with a melting point of 2205 °C. Americium(IV) oxide is the main form of... | Americium | Wikipedia | 487 | 900 | https://en.wikipedia.org/wiki/Americium | Physical sciences | Chemical elements_2 | null |
The tetravalent americium(IV) fluoride (AmF4) is obtained by reacting solid americium(III) fluoride with molecular fluorine:
2AmF3 + F2 -> 2AmF4
Another known form of solid tetravalent americium fluoride is KAmF5. Tetravalent americium has also been observed in the aqueous phase. For this purpose, black Am(OH)4 was ... | Americium | Wikipedia | 478 | 900 | https://en.wikipedia.org/wiki/Americium | Physical sciences | Chemical elements_2 | null |
Chalcogenides and pnictides
The known chalcogenides of americium include the sulfide AmS2, selenides AmSe2 and Am3Se4, and tellurides Am2Te3 and AmTe2. The pnictides of americium (243Am) of the AmX type are known for the elements phosphorus, arsenic, antimony and bismuth. They crystallize in the rock-salt lattice.
Sil... | Americium | Wikipedia | 474 | 900 | https://en.wikipedia.org/wiki/Americium | Physical sciences | Chemical elements_2 | null |
Biological aspects
Americium is an artificial element of recent origin, and thus does not have a biological requirement. It is harmful to life. It has been proposed to use bacteria for removal of americium and other heavy metals from rivers and streams. Thus, Enterobacteriaceae of the genus Citrobacter precipitate amer... | Americium | Wikipedia | 376 | 900 | https://en.wikipedia.org/wiki/Americium | Physical sciences | Chemical elements_2 | null |
About 18 isotopes and 11 nuclear isomers are known for americium, having mass numbers 229, 230, and 232 through 247. There are two long-lived alpha-emitters; 243Am has a half-life of 7,370 years and is the most stable isotope, and 241Am has a half-life of 432.2 years. The most stable nuclear isomer is 242m1Am; it has a... | Americium | Wikipedia | 474 | 900 | https://en.wikipedia.org/wiki/Americium | Physical sciences | Chemical elements_2 | null |
The amount of americium in a typical new smoke detector is 1 microcurie (37 kBq) or 0.29 microgram. This amount declines slowly as the americium decays into neptunium-237, a different transuranic element with a much longer half-life (about 2.14 million years). With its half-life of 432.2 years, the americium in a smoke... | Americium | Wikipedia | 462 | 900 | https://en.wikipedia.org/wiki/Americium | Physical sciences | Chemical elements_2 | null |
One more proposal which utilizes the high nuclear fission rate of 242mAm is a nuclear battery. Its design relies not on the energy of the emitted by americium alpha particles, but on their charge, that is the americium acts as the self-sustaining "cathode". A single 3.2 kg 242mAm charge of such battery could provide ab... | Americium | Wikipedia | 460 | 900 | https://en.wikipedia.org/wiki/Americium | Physical sciences | Chemical elements_2 | null |
^{243}_{95}Am ->[\ce{(n,\gamma)}] ^{244}_{95}Am ->[\beta^-][10.1 \ \ce{h}] ^{244}_{96}Cm
Irradiation of 241Am by 12C or 22Ne ions yields the isotopes 247Es (einsteinium) or 260Db (dubnium), respectively. Furthermore, the element berkelium (243Bk isotope) had been first intentionally produced and identified by bombardi... | Americium | Wikipedia | 462 | 900 | https://en.wikipedia.org/wiki/Americium | Physical sciences | Chemical elements_2 | null |
If consumed, most of the americium is excreted within a few days, with only 0.05% absorbed in the blood, of which roughly 45% goes to the liver and 45% to the bones, and the remaining 10% is excreted. The uptake to the liver depends on the individual and increases with age. In the bones, americium is first deposited ov... | Americium | Wikipedia | 294 | 900 | https://en.wikipedia.org/wiki/Americium | Physical sciences | Chemical elements_2 | null |
Astatine is a chemical element; it has symbol At and atomic number 85. It is the rarest naturally occurring element in the Earth's crust, occurring only as the decay product of various heavier elements. All of astatine's isotopes are short-lived; the most stable is astatine-210, with a half-life of 8.1 hours. Consequen... | Astatine | Wikipedia | 500 | 901 | https://en.wikipedia.org/wiki/Astatine | Physical sciences | Chemical elements_2 | null |
The bulk properties of astatine are not known with any certainty. Research is limited by its short half-life, which prevents the creation of weighable quantities. A visible piece of astatine would immediately vaporize itself because of the heat generated by its intense radioactivity. It remains to be seen if, with suff... | Astatine | Wikipedia | 433 | 901 | https://en.wikipedia.org/wiki/Astatine | Physical sciences | Chemical elements_2 | null |
Evidence for (or against) the existence of diatomic astatine (At2) is sparse and inconclusive. Some sources state that it does not exist, or at least has never been observed, while other sources assert or imply its existence. Despite this controversy, many properties of diatomic astatine have been predicted; for exampl... | Astatine | Wikipedia | 360 | 901 | https://en.wikipedia.org/wiki/Astatine | Physical sciences | Chemical elements_2 | null |
Astatine has an electronegativity of 2.2 on the revised Pauling scale – lower than that of iodine (2.66) and the same as hydrogen. In hydrogen astatide (HAt), the negative charge is predicted to be on the hydrogen atom, implying that this compound could be referred to as astatine hydride according to certain nomenclatu... | Astatine | Wikipedia | 492 | 901 | https://en.wikipedia.org/wiki/Astatine | Physical sciences | Chemical elements_2 | null |
Only a few compounds with metals have been reported, in the form of astatides of sodium, palladium, silver, thallium, and lead. Some characteristic properties of silver and sodium astatide, and the other hypothetical alkali and alkaline earth astatides, have been estimated by extrapolation from other metal halides.
Th... | Astatine | Wikipedia | 421 | 901 | https://en.wikipedia.org/wiki/Astatine | Physical sciences | Chemical elements_2 | null |
With oxygen, there is evidence of the species AtO− and AtO+ in aqueous solution, formed by the reaction of astatine with an oxidant such as elemental bromine or (in the last case) by sodium persulfate in a solution of perchloric acid. The species previously thought to be has since been determined to be , a hydrolysis ... | Astatine | Wikipedia | 363 | 901 | https://en.wikipedia.org/wiki/Astatine | Physical sciences | Chemical elements_2 | null |
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