Arsenic From Wikipedia, the free encyclopedia Arsenic 33As Hydrogen (diatomic nonmetal) Helium (noble gas) Lithium (alkali metal) Beryllium (alkaline earth metal) Boron (metalloid) Carbon (polyatomic nonmetal) Nitrogen (diatomic nonmetal) Oxygen (diatomic nonmetal) Fluorine (diatomic nonmetal) Neon (noble gas) Sodium (alkali metal) Magnesium (alkaline earth metal) Aluminium (other metals) Silicon (metalloid) Phosphorus (polyatomic nonmetal) Sulfur (polyatomic nonmetal) Chlorine (diatomic nonmetal) Argon (noble gas) Potassium (alkali metal) Calcium (alkaline earth metal) Scandium (transition metal) Titanium (transition metal) Vanadium (transition metal) Chromium (transition metal) Manganese (transition metal) Iron (transition metal) Cobalt (transition metal) Nickel (transition metal) Copper (transition metal) Zinc (transition metal) Gallium (other metals) Germanium (metalloid) Arsenic (metalloid) Selenium (polyatomic nonmetal) Bromine (diatomic nonmetal) Krypton (noble gas) Rubidium (alkali metal) Strontium (alkaline earth metal) Yttrium (transition metal) Zirconium (transition metal) Niobium (transition metal) Molybdenum (transition metal) Technetium (transition metal) Ruthenium (transition metal) Rhodium (transition metal) Palladium (transition metal) Silver (transition metal) Cadmium (transition metal) Indium (other metals) Tin (other metals) Antimony (metalloid) Tellurium (metalloid) Iodine (diatomic nonmetal) Xenon (noble gas) Caesium (alkali metal) Barium (alkaline earth metal) Lanthanum (lanthanide) Cerium (lanthanide) Praseodymium (lanthanide) Neodymium (lanthanide) Promethium (lanthanide) Samarium (lanthanide) Europium (lanthanide) Gadolinium (lanthanide) Terbium (lanthanide) Dysprosium (lanthanide) Holmium (lanthanide) Erbium (lanthanide) Thulium (lanthanide) Ytterbium (lanthanide) Lutetium (lanthanide) Hafnium (transition metal) Tantalum (transition metal) Tungsten (transition metal) Rhenium (transition metal) Osmium (transition metal) Iridium (transition metal) Platinum (transition metal) Gold (transition metal) Mercury (transition metal) Thallium (other metals) Lead (other metals) Bismuth (other metals) Polonium (other metals) Astatine (metalloid) Radon (noble gas) Francium (alkali metal) Radium (alkaline earth metal) Actinium (actinide) Thorium (actinide) Protactinium (actinide) Uranium (actinide) Neptunium (actinide) Plutonium (actinide) Americium (actinide) Curium (actinide) Berkelium (actinide) Californium (actinide) Einsteinium (actinide) Fermium (actinide) Mendelevium (actinide) Nobelium (actinide) Lawrencium (actinide) Rutherfordium (transition metal) Dubnium (transition metal) Seaborgium (transition metal) Bohrium (transition metal) Hassium (transition metal) Meitnerium (unknown chemical properties) Darmstadtium (unknown chemical properties) Roentgenium (unknown chemical properties) Copernicium (transition metal) Ununtrium (unknown chemical properties) Flerovium (unknown chemical properties) Ununpentium (unknown chemical properties) Livermorium (unknown chemical properties) Ununseptium (unknown chemical properties) Ununoctium (unknown chemical properties) P ↑ As ↓ Sb germanium ← arsenic → selenium Arsenic in the periodic table Appearance metallic grey General properties Name, symbol, number arsenic, As, 33 Pronunciation /ˈɑrsɨnɪk/ ar-sə-nik, also /ɑrˈsɛnɪk/ ar-sen-ik when attributive Element category metalloid Group, period, block 15 (pnictogens), 4, p Standard atomic weight 74.921595(6) Electron configuration [Ar] 4s2 3d10 4p3 2, 8, 18, 5 Physical properties Phase solid Density (near r.t.) 5.727 g·cm−3 Liquid density at m.p. 5.22 g·cm−3 Sublimation point 887 K, 615 °C, 1137 °F Triple point 1090 K, 3628[1] kPa Critical point 1673 K, ? MPa Heat of fusion (grey) 24.44 kJ·mol−1 Heat of vaporization ? 34.76 kJ·mol−1 Molar heat capacity 24.64 J·mol−1·K−1 Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 553 596 646 706 781 874 Atomic properties Oxidation states 5, 3, 2, 1,[2] -3 (mildly acidic oxide) Electronegativity 2.18 (Pauling scale) Ionization energies (more) 1st: 947.0 kJ·mol−1 2nd: 1798 kJ·mol−1 3rd: 2735 kJ·mol−1 Atomic radius 119 pm Covalent radius 119±4 pm Van der Waals radius 185 pm Miscellanea Crystal structure simple trigonal[3] Arsenic has a simple trigonal crystal structure Magnetic ordering diamagnetic[4] Electrical resistivity (20 °C) 333 nΩ·m Thermal conductivity 50.2 W·m−1·K−1 Young's modulus 8 GPa Bulk modulus 22 GPa Mohs hardness 3.5 Brinell hardness 1440 MPa CAS registry number 7440-38-2 History Discovery Early Bronze Age (2500 BC) First isolation Albertus Magnus (1250) Most stable isotopes Main article: Isotopes of arsenic iso NA half-life DM DE (MeV) DP 73As syn 80.3 d ε - 73Ge γ 0.05D, 0.01D, e - 74As syn 17.78 d ε - 74Ge β+ 0.941 74Ge γ 0.595, 0.634 - β− 1.35, 0.717 74Se 75As 100% 75As is stable with 42 neutrons v t e · references Arsenic is a chemical element with symbol As and atomic number 33. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.[5] Arsenic is a metalloid. It can exist in various allotropes, although only the gray form has important use in industry. The main use of metallic arsenic is for strengthening alloys of copper and especially lead (for example, in car batteries). Arsenic is a common n-type dopant in semiconductor electronic devices, and the optoelectronic compound gallium arsenide is the most common semiconductor in use after doped silicon. Arsenic and its compounds, especially the trioxide, are used in the production of pesticides, treated wood products, herbicides, and insecticides. These applications are declining, however.[6] Arsenic is notoriously poisonous to multicellular life, although a few species of bacteria are able to use arsenic compounds as respiratory metabolites. Arsenic contamination of groundwater is a problem that affects millions of people across the world. Contents [hide] 1 Characteristics 1.1 Physical characteristics 1.2 Isotopes 1.3 Chemistry 2 Compounds 2.1 Inorganic compounds 2.1.1 Alloys 2.2 Organoarsenic compounds 3 Occurrence and production 4 History 5 Applications 5.1 Agricultural 5.2 Medical use 5.3 Alloys 5.4 Military 5.5 Other uses 6 Biological role 6.1 Bacteria 6.2 Heredity 6.3 Biomethylation 7 Environmental issues 7.1 Exposure 7.2 Occurrence in drinking water 7.2.1 San Pedro de Atacama 7.3 Wood preservation in the US 7.4 Mapping of industrial releases in the US 8 Toxicity and precautions 8.1 Classification 8.2 Legal limits, food, and drink 8.3 Biological mechanism 8.4 Exposure risks and remediation 8.5 Treatment 9 See also 10 References 11 Bibliography 12 Further reading 13 External links Characteristics[edit] Physical characteristics[edit] Crystal structure common to Sb, AsSb and gray As The three most common arsenic allotropes are metallic gray, yellow and black arsenic, with gray being the most common.[7] Gray arsenic (α-As, space group R3m No. 166) adopts a double-layered structure consisting of many interlocked ruffled six-membered rings. Because of weak bonding between the layers, gray arsenic is brittle and has a relatively low Mohs hardness of 3.5. Nearest and next-nearest neighbors form a distorted octahedral complex, with the three atoms in the same double-layer being slightly closer than the three atoms in the next.[8] This relatively close packing leads to a high density of 5.73 g/cm3.[9] Gray arsenic is a semimetal, but becomes a semiconductor with a bandgap of 1.2–1.4 eV if amorphized.[10] Gray arsenic is also the most stable form.Yellow arsenic is soft and waxy, and somewhat similar to tetraphosphorus (P 4). Both have four atoms arranged in a tetrahedral structure in which each atom is bound to each of the other three atoms by a single bond. This unstable allotrope, being molecular, is the most volatile, least dense and most toxic. Solid yellow arsenic is produced by rapid cooling of arsenic vapor, As 4. It is rapidly transformed into the gray arsenic by light. The yellow form has a density of 1.97 g/cm3.[9] Black arsenic is similar in structure to red phosphorus.[9] Black arsenic can also be formed by cooling vapor at around 100–220 °C. It is glassy and brittle. It is also a poor electrical conductor.[11] Isotopes[edit] Main article: Isotopes of arsenic Naturally occurring arsenic is composed of one stable isotope, 75As.[12] This makes it a monoisotopic element. As of 2003, at least 33 radioisotopes have also been synthesized, ranging in atomic mass from 60 to 92. The most stable of these is 73As with a half-life of 80.30 days. All other isotopes have half-lives of under one day, with the exception of 71As (t½=65.30 hours), 72As (t½=26.0 hours), 74As (t½=17.77 days), 76As (t½=1.0942 days), and 77As (t½=38.83 hours). Isotopes that are lighter than the stable 75As tend to decay by β+ decay, and those that are heavier tend to decay by β− decay, with some exceptions. At least 10 nuclear isomers have been described, ranging in atomic mass from 66 to 84. The most stable of arsenic's isomers is 68mAs with a half-life of 111 seconds.[12] Chemistry[edit] When heated in air, arsenic oxidizes to arsenic trioxide; the fumes from this reaction have an odor resembling garlic. This odor can be detected on striking arsenide minerals such as arsenopyrite with a hammer. Arsenic (and some arsenic compounds) sublimes upon heating at atmospheric pressure, converting directly to a gaseous form without an intervening liquid state at 887 K (614 °C).[1] The triple point is 3.63 MPa and 1,090 K (820 °C).[9][1] Arsenic makes arsenic acid with concentrated nitric acid, arsenious acid with dilute nitric acid, and arsenic trioxide with concentrated sulfuric acid.[13]