Atomic number:2

Group numbers:18

Period:1

Electronic configuration:1s²

Formal oxidation number:0

Electronegativities:-

Atomic radius / pm:128

Relative atomic mass:4.002602 ± 0.000002

 

Helium was discovered by Pierre Jules César Janssen (FR) and Sir Joseph Norman Lockyer (GB) in 1868. The origin of the name comes from the Greek word helios meaning sun. It is a light, odourless, colourless inert gas. Helium is the second most abundant element in the universe. Helium is found in natural gas deposits from wells in Texas, Oklahoma and Kansas. It is used in balloons, deep sea diving and welding and in very low temperature research.

Density / g dm^-3:~1760 (solid, 6.9 MPa)

 124.8 (liquid, m.p.)

 0.1785 (gas, 273 K)

Molar volume / cm³mol^-1:~2.27 (solid, 6,9 MPa)

 32.07 (liquid, m.p.)

 22423.54 (gas, 273 K)

Electrical resistivity / μΩcm:- (20 °C)

Thermal conductivity / W m^-1K^-1:0.155

Melting point / °C:-272.2

Boiling point / °C:-268.93

Heat of fusion / kJ mol^-1:0.021

Heat of vaporization / kJ mol^-1:0.082

Heat of atomization / kJ mol^-1:0

1st ionization energy / kJ mol^-1:2372.34

2nd ionization energy / kJ mol^-1:5250.56

3rd ionization energy / kJ mol^-1:-

in the atmosphere / ppm:5.2

in the Earth's crust / ppm:0.008

in the oceans / ppm:0.0000072