A colorless, highly flammable, lighter-than-air, gaseous chemical element. Hydrogen’s symbol is H, its atomic number is 1, and its atomic weight is 1.00797. Hydrogen is the lightest of all of the chemical elements.

An atom of hydrogen has one proton and no neutrons in its nucleus, and spinning around this nucleus is only one electron. A molecule of hydrogen gas is made up of two atoms of hydrogen (H2). Hydrogen gas is colorless, tasteless and lighter than air. It is used as a fuel gas for welding.