Periodic Table


Atomic number: 33
Atomic weight: 74.92160
Symbol: As
Group number: 15
Electronic configuration: [Ar].3d10.4s2.4p3


Elemental arsenic occurs in two solid modifications: yellow, and grey or metallic, with specific gravities of 1.97, and 5.73, respectively. The element is a steel grey, very brittle, crystalline, semimetallic (metalloid) solid. It tarnishes in air, and when heated rapidly oxidises to arsenous oxide which has a garlic odour.

Arsenic and its compounds are poisonous as any reader of "who-done-it" books knows. Upon heating arsenic and some minerals containing arsenic, it sublimes (transfers from the solid to the gaseous state, without passing through the liquid state).

General information

Discoveror: Known since ancient times
Date discovered:
Discovered at: not known
Meaning of name: From the Greek word "arsenikon" meaning "yellow orpiment"

Physical data

Standard state: solid at 298 K
Colour: metallic grey
Density of solid at ambient temperature/kg m-3: 5727
Molar volume/cm3: 12.95

Radii /pm

Atomic: 114
Covalent (single bond):
Pauling radius for the ion [As]-: 285

Valence shell orbital radius maxima (Rmax)
orbital s p d f
radius88.5106.625.4no data


Both values are quoted on the Pauling scale.

Pauling: 2.18
Allred Rochow: 2.20

Crystal Structure

structure: trigonal

The following CrystalMaker image represents the solid state structure. For most elements, the most stable allotrope is illustrated. Try WebElements version 2 for interactive virtual reality and CHIME images.


Temperatures (/K)

melting point: 1090
boiling point: 887

Enthalpies /kJ mol-1

fusion: 27.7
vaporization: 32.4

single bond enthalpies:
As-F As-Cl As-Br As-I As-As
406 322 258 200 382.0

Ionization enthalpies /kJ mol-1

Number Enthalpy


This section gives some data for naturally occurring isotopes.
Nominal mass Accurate mass % natural abundance
75As74.9215942 (17)100

Further Information

Copyright 1997 Mark Winter
Department of Chemistry at the University of Sheffield, Sheffield S3 7HF, England.

The current version of this document is at http://www.shef.ac.uk/~chem/web-elements-I/As.html