PERIODIC ELEMENT
He (Helium)

 



Atomic number : 2
Atomic mass : 4.00260 g.mol-1
Electronegativity according to Pauling : 2.1
Density : 0.178*10-3 g.cm-3 at 20 °C
Melting point : - 272.2 (26 atm) °C
Boiling point : - 268.9 °C
Vanderwaals radius : 0.118 nm
Ionic radius : unknown
Isotopes : 2
Electronic shell : 1s2
Energy of first ionisation : 2372 kJ.mol-1
Discovered by : Sir William Ramsey in 1895
 
Atomic Structure Uses (balloons, deep sea diving)