The periodic table/Hydrogen

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Hydrogen was discovered in 1776 by Henry Cavendish in London, UK. Antoine Lavoisier gave the element its name, derived from the Greek 'hydro' and 'genes' meaning water-forming.

Quick Facts[edit]

Name: Hydrogen

Symbol: H

Mass: 1.00794

Atomic Number: 1

Electron Configuration: 1s1

Classification: non-metal

CAS Number: 133-74-0

Appearance: colourless gas

Discovery in: 1776

Key Isotopes: 1H, 2H

Allotropes: H2

Density: 0.08988 g/L

Crystal Structure: hexagonal

Melting Point: -259.1 °C

Boiling Point: -252.9 °C


Hydrogen can form an explosive mixture from air. It is currently manufactured from methane gas, but can also be made through the electrolysis of water and aqueous salts. Hydrogen gas is used to make key materials like ammonia, cyclohexane and methanol, which are intermediates in the production of fertilisers, plastics and pharmaceuticals.

Large quantities of hydrogen are used in the Haber process and for the hydrogenation of oils from fats.

Hydrogen is part of the DNA molecule.

Hydrogen is found in the sun and most of the stars, and is the most abundant element in the universe. The planet Jupiter is composed mostly of hydrogen, and there is a theory that in the interior of the planet the pressure is so great that metallic hydrogen is formed from solid molecular hydrogen. On Earth, hydrogen is found in the greatest quantities in water, only being present in the atmosphere in small amounts - less than 1 part per million by volume.

Atomic Data[edit]

Atomic radius: 1.100 Å

Covalent radius: 0.32 Å

Electronegativity: 2.200

Electron affinity: 72.7 kJ mol-1

First ionisation energy: 1312.0 kJ mol-1

Supply Risk[edit]


Oxidation States and Isotopes[edit]

Common oxidation states: 1, -1


Isotope Atomic mass Abundance (%) Half life Mode of decay
1H 1.008 99.988
2H 2.014 0.012
3H 3.016 12.31 years β-

Pressure and Temperature Data[edit]

Molar heat capacity: 28.836 J mol-1 K-1

See Also[edit]