Name: helium
Symbol: He
Atomic number: 2
Atomic weight: 4.002602 (2) g r
Group in periodic table: 18
Group name: Noble gas
Period in periodic table: 1
Block in periodic table: p-block
CAS registry ID: 7440-59-7
Helium is one of the so-called noble gases. Helium gas is unreactive, colourless, and odourless. Helium is available in pressurised tanks.
Elemental helium is a colourless odourless monoatomic gas. Helium is the second most abundant element in the universe after hydrogen. a particles are doubly ionised helium atoms, He2+.
Helium is used in lighter than air balloons and while heavier than hydrogen, is far safer since helium does not burn. Speaking after breathing an atmosphere rich in helium results in a squeaky voice (don't try it!).