WebElements

Periodic Table

argon

Atomic number: 18
Atomic weight: 39.948
Symbol: Ar
Group number: 18
Electronic configuration: [Ne].3s2.3p6

Description

Argon is colourless and odourless. Argon is very inert and is not known to form true chemical compounds. It makes a good atmosphere for working with air-sensitive materials since it is heavier than air and less reactive than N2.

General information

Discoveror: Sir William Ramsay, Lord Rayleigh
Date discovered: 1894
Discovered at: Scotland
Meaning of name: From the Greek word "argos" meaning "inactive"

Physical data

Standard state: gas at 298 K
Colour: colourless
Density of solid at ambient temperature/kg m-3: no data
Molar volume/cm3: 22.56

Radii /pm

Atomic: 71
Covalent (single bond):
Pauling radius for the ion [Ar]-: no data

Valence shell orbital radius maxima (Rmax)
orbital s p d f
radius62.668.8no datano data

Electronegativities

Both values are quoted on the Pauling scale.

Pauling: no data
Allred Rochow: 3.20

Crystal Structure

structure: ccp (cubic close-packed)

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.

ball-and-stick.gif

Temperatures (/K)

melting point: 83.8
boiling point: 87.3

Enthalpies /kJ mol-1

fusion: 1.18
vaporization: 6.5

single bond enthalpies:
Ar-F Ar-Cl Ar-Br Ar-I Ar-Ar
no data no data no data no data 4.73

Ionization enthalpies /kJ mol-1

Number Enthalpy
1st1520.5
2nd2665.8
3rd3931
4th5771
5th7238
6th8780
7th12000
8th13844

Isotopes

This section gives some data for naturally occurring isotopes.
Nominal mass Accurate mass % natural abundance
36Ar35.96754552 (29)0.337 (3)
38Ar37.9627325 (9)0.063 (1)
40Ar39.9623837 (14)99.600 (3)

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/Ar.html