(From the Greek helios, "the sun") A colorless, odorless, chemical element, one of the noble gases, having the lowest known boiling and melting points. It is used in cryogenics, as a diluent for oxygen, in deep-sea breathing systems, for inflating balloons, as a protective gas in growing silicon and germanium crystals and in titanium and zirconium production, and as an inert gas shield for arc welding.
Symbol: He
Atomic number: 2
Atomic weight: 4.00260
Density (at 0°
C with 101,325
pascals): 0.179
g/
L
Melting point (at 26 standard
atmospheres of
pressure): -272.2°
C
Boiling point: -268.93°
C
Valence: 0
Ground state electron configuration: 1s
2