The periodic table/Hydrogen

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Pronunciation of Hydrogen

Discovery

In 1766, hydrogen was discovered by English philosopher Henry Cavendish in London, UK. Although hydrogen was officially discovered in 1766, scientists previously have been producing hydrogen as early as approximately a century ago - as written by Anglo-Irish chemist Robert Boyle. French chemist Antoine Lavoisier gave the element its name "hydrogen", derived from the Greek 'hydro' (ὑδρο) and 'genes' (γενής) , meaning "water-forming".

Quick Facts

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

Uses

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

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

Unknown

Oxidation States and Isotopes

Common oxidation states: 1, -1

Isotopes

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

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