Living Reference Work Entry

Encyclopedia of Geochemistry

Part of the series Encyclopedia of Earth Sciences Series pp 1-2

Date: Latest Version


  • Monica VasiliuAffiliated withDepartment of Chemistry, University of Alabama Email author 
  • , David A. DixonAffiliated withDepartment of Chemistry, University of Alabama Email author 

Element Data

Atomic Symbol: As

Atomic Number: 33

Atomic Weight: 74.9216

Isotopes and Abundances: 75As 100 %

1 Atm Melting Point: 1090 K

1 Atm Boiling Point: 887 K (sublimes)

Common Valences: +5, +3, and −3

Ionic Radii: (+V) 46, (+III) 69, and (−III) 222 ppm

Pauling Electronegativity: 2.18

First Ionization Energy: 947.0 kJ/mol

Chondritic (CI) Abundance: 1.86 ppm

Silicate Earth Abundance: 0.05 ppm

Crustal Abundance: 2.1 ppm

Seawater Abundance: 0.0026 ppm

Core Abundance: 5 ppm


Arsenic (Emsley 1991, 2001; Anthoni 2006; Anders and Grevesse 1989; McDonough 2005), a metalloid, has three allotropic forms: yellow, black, and gray. The most common form is a shiny, gray, brittle, metallic-looking crystalline solid. The less common yellow form is a crystalline solid which is produced when vapors of arsenic are cooled suddenly. It tarnishes rapidly in air and when heated does not melt, but sublimes although it can be forced to melt as well. When arsenic is heated in air, it reacts with o ...

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