Helium

Symbol: He
Atomic number: 2
Category: noble gases
Group: 18
Period: 1
Block: s
Atomic weight: 4.002602 g/mol
Electrons per shell: 2
CAS number: 7440-59-7
Phase: gas
Density: 0.1786 g/l (0 °C, 101.325 kPa)
Melting point: 0.95 K (-272.20 °C, -457.96 °F) (at 2.5 MPa)
Boiling point: 4.22 K (-268.93 °C, -452.07 °F)
Crystal structure: hexagonal close-packed
Oxidation states: 0
Electronegativity: unknown
Name's origin: Helios
Name's meaning: the Greek name for Sun because the discoverer concluded this element is found in the Sun
Facts:
- is a colorless, odorless, tasteless, non-toxic, inert monatomic gas
- its boiling and melting points are the lowest among the elements and it exists only as a gas except in extreme conditions
- is used in cryogenics, in deep-sea breathing systems, to cool superconducting magnets, in helium dating, for inflating balloons, for providing lift in airships and as a protective gas for many industrial uses
- inhaling a small volume of the gas temporarily changes the timbre and quality of the human voice
- is the second lightest element and is the second most abundant in the observable Universe
- most helium was formed during the Big Bang, but new helium is being created as a result of the nuclear fusion of hydrogen in stars
- has two liquid states - helium I and helium II - helium II is a superfluid
- at standard conditions is non-toxic, plays no biological role and is found in trace amounts in human blood - if enough helium is inhaled that oxygen needed for normal respiration is replaced asphyxia is possible