Atomic # = 2
Atomic weight = 4.002
Helium was first discovered on the sun though an analysis of the solar spectrum. At normal temperatures and pressures, helium exists as a monoatomic gas. The density of helium gas (0.2 grams per liter) is less than that of air (1.2 grams per liter), and because of this a balloon filled with helium will float in air.