THE ELEMENTS OF BARIUM
ALKALINE EARTH METAL
Barium was discovered by Sir Humphry Davy (GB) in1808.Theoriginofthe name comes from theGreekwordbarysmeaningheavy. It is asoft,slightlymalleable,silvery-whitemetal. Barium oxidises in airandreactswith water.Solublecompounds are toxic by ingestion. Bariumisfoundinbarytine(BaSO4) and witherite (BaCO3), it is neverfoundinpureform dueto its reactivity. Barium must be storedunderkerosenetoremainpure. Barite, or barium sulfate (BaSO4) isused asafilterforrubber, plastics and resins. It is insoluble inwaterandsoisused in X-rays of the digestivesystem.Bariumnitrate,Ba(NO3)2,burns brilliant green and isusedinfireworks.
Atomic number:56
Group numbers:2
Period:6
Electronic configuration:[Xe]6s2
Formal oxidation number:+2
Electronegativities:0.89
Atomic radius / pm:217.4
Relative atomic mass:137.327±0.007
THERMAL PROPERTIES
Thermal conductivity / Wm-1K-1:18.4
Melting point / °C:727
Boiling point / °C:1897
Heat of fusion / kJ mol-1:7.66
Heat of vaporization / kJ mol-1:150.9
Heat of atomization / kJ mol-1:180.7
CRYSTALLOGRAPHIC DATA
Crystal structure:
body-centered cubic
Unit-cell dimensions / pm:
a=502.5
Space group:
Im3m
PHYSICAL PROPERTIES
Density / g dm-3:3594(293 K)
3325 (m.p.)
Molar volume / cm3mol-1:38.21 (293 K)
41.30 (m.p.)
Electrical resistivity / μΩcm:50(20 °C)
IONIZATION ENERGIES
1st ionization energy / kJ mol-1:502.86
2nd ionization energy / kJ mol-1:965.24
3rd ionization energy / kJ mol-1:-
ABUNDANCE OF ELEMENTS
in the atmosphere / ppm:-
in the Earth's crust / ppm:250
in the oceans / ppm:0.03
ISOTOPES
IsotopeRelativeatomicmassMasspercent(%)
130Ba129.906310(7)0.106(2)
132Ba131.905056(3)0.101(2)
134Ba133.904503(3)2.417(27)
135Ba134.905683(3)6.592(18)
136Ba135.904570(3)7.854(36)
137Ba136.905821(3)11.23(4)
138Ba137.905241(3)71.70(7)
REDUCTION POTENTIALS
Balanced half-reaction Eo / V
Ba
2+ + 2e
- 
Ba
(s)- 2.906BaO + 2H
+ + 2e
- Ba
(s) + H
2O
- 2.166
55Caesium <= 56Barium => 57Lanthanum
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