The chemical formula for hydrogen gas is H2. Its molar mass is 2.016 grams per mole, and it exists as a gas at standard temperature and pressure, where its density is 0.09 grams per liter. Hydrogen's melting point is -434.49 degrees Fahrenheit and its boiling point is -423.182 degrees Fahrenheit.
Hydrogen is the simplest chemical and the first element in the periodic table of elements. The atom of its most common isotope is composed of one proton and one electron. Hydrogen is also the most abundant element in the universe and the main constituent of stars. Inside the stars, hydrogen atoms are fused together to produce helium.