Periodic Table


Atomic number: 56
Atomic weight: 137.327
Symbol: Ba
Group number: 2
Electronic configuration: [Xe].6s2


Barium is a metallic element, soft, and when pure is silvery white like lead. The metal oxidises very easily. It is decomposed by water or alcohol. Barium is one of the alkaline-earth metals. Small amounts of barium compounds are used in paints and glasses.

General information

Discoveror: Sir Humphrey Davy
Date discovered: 1808
Discovered at: England
Meaning of name: From the Greek word "barys" meaning "heavy"

Physical data

Standard state: solid at 298 K
Colour: silvery white
Density of solid at ambient temperature/kg m-3: 3510
Molar volume/cm3: 38.16

Radii /pm

Atomic: 253
Covalent (single bond):
Pauling radius for the ion [Ba]-: no data

Valence shell orbital radius maxima (Rmax)
orbital s p d f
radius235.4no datano datano data


Both values are quoted on the Pauling scale.

Pauling: 0.89
Allred Rochow: 0.97

Crystal Structure

structure: bcc (body-centred cubic)

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: 1000
boiling point: 2143

Enthalpies /kJ mol-1

fusion: 8.0
vaporization: 140.2

single bond enthalpies:
Ba-F Ba-Cl Ba-Br Ba-I Ba-Ba
578 475 427 360 no data

Ionization enthalpies /kJ mol-1

Number Enthalpy


This section gives some data for naturally occurring isotopes.
Nominal mass Accurate mass % natural abundance
130Ba129.906282 (8)0.106 (2)
132Ba131.905042 (9)0.101 (2)
134Ba133.904486 (7)2.417 (27)
135Ba134.90566597)6.592 (18)
136Ba135.904553 (7)7.854 (39)
137Ba136.905812 (6)11.23 (4)
138Ba137.905232 (6)71.70 (7)

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/Ba.html