Hydrogen is the most abundant element in the universe. It is also the lightest element and is so light and diffusive that uncombined hydrogen can escape from the atmosphere. Hydrogen gas ordinarily is a mixture of two molecular forms, ortho- and para-hydrogen, which differ by the spins of their electrons and nuclei. Normal hydrogen at room temperature consists of 25% of the para form and 75% of the ortho form.



Physical Properties

Hydrogen, symbol H, is one of the atoms making up water and also one of the atoms in all hydrocarbons and is therefore readily available everywhere on the earth. Hydrogen has an atomic number of 1.

Gas Hydrogen
Chemical formula H2
Molecular weight 2.0
Gas density 0.08988 Kg/m3
SG vapour 0.07
Boiling point -253°C
Critical temperature -240°C
Critical pressure 12.98 bar


Hydrogen occurs in the free state in volcanic gases and some natural gases. Hydrogen is produced by electrolysis of water and is collected at the negative electrode (cathode). It is also prepared by steam on heated carbon, decomposition of certain hydrocarbons with heat, action of sodium or potassium hydroxide on aluminum, or displacement from acids by certain metals.


Hydrogen is highly flammable and also in high enough concentrations may cause asphyxiation and death. For more detail on the hazards associated with hydrogen check the Safety Data sheet.

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