Arsenic

This article is about the chemical element. For the poison commonly called "arsenic", see arsenic trioxide. For other uses, see Arsenic (disambiguation).
Arsenic, 33As
Arsenic
Pronunciation
Allotropesgrey (most common), yellow, black (see Allotropes of arsenic)
Appearancemetallic grey
Standard atomic weight Ar°(As)
Arsenic in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
P
↑
As
↓
Sb
germanium ← arsenic → selenium
Atomic number (Z)33
Groupgroup 15 (pnictogens)
Periodperiod 4
Block  p-block
Electron configuration[Ar] 3d10 4s2 4p3
Electrons per shell2, 8, 18, 5
Physical properties
Phase at STPsolid
Sublimation point887 K ​(615 °C, ​1137 °F)
Density (at 20° C)grey: 5.782 g/cm3[3]
when liquid (at m.p.)5.22 g/cm3
Triple point1090 K, ​3628 kPa[4]
Critical point1673 K, ? MPa
Heat of fusiongrey: 24.44 kJ/mol
Heat of vaporization34.76 kJ/mol (?)
Molar heat capacity24.64 J/(mol·K)
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 statescommon: −3, +3, +5
−2,? −1,? 0,[5] +1,[6] +2,[7] +4?
ElectronegativityPauling scale: 2.18
Ionization energies
  • 1st: 947.0 kJ/mol
  • 2nd: 1798 kJ/mol
  • 3rd: 2735 kJ/mol
  • (more)
Atomic radiusempirical: 119 pm
Covalent radius119±4 pm
Van der Waals radius185 pm
Color lines in a spectral range
Spectral lines of arsenic
Other properties
Natural occurrenceprimordial
Crystal structuregrey: ​rhombohedral (hR2)
Lattice constants
Rhombohedral crystal structure for grey: arsenic
ar = 413.15 pm
α = 54.133° pm ah = 375.99 pm
ch = 1054.58 pm (at 20 °C)[3]
Thermal expansion5.6 µm/(m⋅K)[8] (at r.t.)
Thermal conductivity50.2 W/(m⋅K)
Electrical resistivity333 nΩ⋅m (at 20 °C)
Magnetic orderingdiamagnetic[9]
Molar magnetic susceptibility−5.5×10−6 cm3/mol[10]
Young's modulus8 GPa
Bulk modulus22 GPa
Mohs hardness3.5
Brinell hardness1440 MPa
CAS Number7440-38-2
History
DiscoveryArabic alchemists (before AD 815)
Isotopes of arsenic
Main isotopes[11] Decay
abun­dance half-life (t1/2) mode pro­duct
73As synth 80.3 d ε 73Ge
γ –
74As synth 17.8 d ε 74Ge
β+ 74Ge
γ –
β− 74Se
75As 100% stable
 Category: Arsenic
| references

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 sulfur and metals, but also as a pure elemental crystal. It has various allotropes, but only the grey form, which has a metallic appearance, is important to industry.

The primary use of arsenic is in alloys of lead (for example, in car batteries and ammunition). Arsenic is a common n-type dopant in semiconductor electronic devices. It is also a component of the III–V compound semiconductor gallium arsenide. Arsenic and its compounds, especially the trioxide, are used in the production of pesticides, treated wood products, herbicides, and insecticides. These applications are declining with the increasing recognition of the toxicity of arsenic and its compounds.[12]

Arsenic has been known since ancient times to be poisonous to humans.[13] However, a few species of bacteria are able to use arsenic compounds as respiratory metabolites. Trace quantities of arsenic have been proposed to be an essential dietary element in rats, hamsters, goats, and chickens. Research has not been conducted to determine whether small amounts of arsenic may play a role in human metabolism.[14][15] However, arsenic poisoning occurs in multicellular life if quantities are larger than needed. Arsenic contamination of groundwater is a problem that affects millions of people across the world.

The United States' Environmental Protection Agency states that all forms of arsenic are a serious risk to human health.[16] The United States' Agency for Toxic Substances and Disease Registry ranked arsenic number 1 in its 2001 prioritized list of hazardous substances at Superfund sites.[17] Arsenic is classified as a Group-A carcinogen.[16]

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  3. ^ a b Arblaster JW (2018). Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International. ISBN 978-1-62708-155-9.
  4. ^ Gokcen, N. A (1989). "The As (arsenic) system". Bull. Alloy Phase Diagrams. 10: 11–22. doi:10.1007/BF02882166.
  5. ^ Abraham MY, Wang Y, Xie Y, Wei P, Shaefer III HF, Schleyer Pv, Robinson GH (2010). "Carbene Stabilization of Diarsenic: From Hypervalency to Allotropy". Chemistry: A European Journal. 16 (2): 432–5. doi:10.1002/chem.200902840. PMID 19937872.
  6. ^ Ellis BD, MacDonald CL (2004). "Stabilized Arsenic(I) Iodide: A Ready Source of Arsenic Iodide Fragments and a Useful Reagent for the Generation of Clusters". Inorganic Chemistry. 43 (19): 5981–6. doi:10.1021/ic049281s. PMID 15360247.
  7. ^ Greenwood NN, Earnshaw A (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 28. ISBN 978-0-08-037941-8.
  8. ^ Cverna, Fran (2002). ASM Ready Reference: Thermal properties of metals. ASM International. pp. 8–. ISBN 978-0-87170-768-0. pdf.
  9. ^ Lide, David R., ed. (2000). "Magnetic susceptibility of the elements and inorganic compounds". Handbook of Chemistry and Physics (PDF) (81 ed.). CRC press. ISBN 0849304814.
  10. ^ Weast R (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.
  11. ^ Kondev FG, Wang M, Huang WJ, Naimi S, Audi G (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
  12. ^ Grund, Sabina C., Hanusch, Kunibert, Wolf, Hans Uwe. "Arsenic and Arsenic Compounds". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a03_113.pub2. ISBN 978-3527306732.
  13. ^ "Arsenic: A Murderous History | Dartmouth Toxic Metals".
  14. ^ Cite error: The named reference ANut was invoked but never defined (see the help page).
  15. ^ Cite error: The named reference UEssent was invoked but never defined (see the help page).
  16. ^ a b Dibyendu S, Datta R (2007). "Biogeochemistry of Arsenic in Contaminated Soils of Superfund Sites". EPA. United States Environmental Protection Agency. Retrieved 25 February 2018.
  17. ^ Carelton J (2007). "Final Report: Biogeochemistry of Arsenic in Contaminated Soils of Superfund Sites". United States Environmental Protection Agency. Archived from the original on 28 July 2018. Retrieved 25 February 2018.