An inert gaseous element. The atom is characterised by possessing two protons in its nucleus. Usually there two neutrons as well. This abundant form of helium is about four times as heavy as hydrogen. Helium accounts for just under one quarter of the atomic matter in the universe and was principally formed during the first few minutes after the big bang. The isotope, helium-3 very short lived with only 1 neutron, is also important in nucleosynthesis (of elements). Helium is also produced by the nuclear fusion which takes place at the centre of stars on the main sequence.
- In the sun (hence its name) by Norman Lockyer studying the spectral lines in 1868.
|Atomic / Molecular Weight||4.002602||gmol-1||Clip|
|Specific heat capacity||0.00519||Jkg-1K-1||Clip|
|Latent heat of evaporation||25000||Jkg-1||Clip|
|Ratio of Specific Heats||1.667||Clip|
|Refractive index||1.000036||at 589.3nm 101.3kPa 0°C||Clip|
|Velocity of sound||972.5ms-1 @ 0°C||ms-1||Clip|
|de Broglie wavelength||0.000000000081||m||Clip|