Hydrogen (H)

Stable isotopes of hydrogen available from ISOFLEX

Isotope Z(p) N(n) Atomic Mass Natural Abundance Enrichment Level Chemical Form
Deuterium 1 1 2.014101778 0.0115% >99.00% Heavy Water

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Hydrogen was discovered in 1766 by Henry Cavendish, who also independently discovered nitrogen. Its name derives from the Greek words hydro and genes, meaning “water-generator” or “water-creator.”

The most abundant element in the universe, hydrogen is a colorless, odorless, tasteless gas that is also flammable, burning in the air with a popping sound. It combines explosively with oxygen at ordinary temperatures in the presence of finely divided metals. Explosion of its mixture with chlorine is detonated by sunlight, heat or spark. It also combines explosively with halogens, and it autoignites at 574 ºC.

Hydrogen is lighter than air and is slightly soluble in water. It forms the largest number of chemical compounds — more than any other element, including carbon — and is a component of all mineral acids, ammonia, natural gases and hydrocarbons, as well as a vast number of organic compounds, from simple alcohols and aldehydes to complex proteins, carbohydrates and chlorophyll.

The first hydrogen-filled balloon was invented by Jacques Charles in 1783. German Count Ferdinand von Zeppelin later promoted the idea of rigid airships lifted by hydrogen that later were called Zeppelins, the first of which had its maiden flight in 1900. Hydrogen-lifted airships were used as observation platforms and bombers during World War I. Hydrogen has also been used as a coolant in turbogenerators, as battery fuel, for the processing of fossil fuels, in the production of ammonia, as a hydrogenating agent for food oils, and in the production of methanol. It is used as a tracer gas for minute leak detection, as a shielding gas in welding, and in cryogenic research.

Properties of Hydrogen

Name Hydrogen
Symbol H
Atomic number 1
Atomic weight 1.0079
Standard state Gas at 298 °K
CAS Registry ID 1333-74-0 
Group in periodic table
Group name None 
Period in periodic table
Block in periodic table s-block 
Color Colorless
Classification Nonmetallic 
Melting point -259.14 °C
Boiling point -252.87 °C
Thermal conductivity 0.1805 W/(m·K)
Electronegativity 2.20 
Heat of vaporization 0.452 kJ·mol-1
Heat of fusion 0.558  kJ·mol-1
Density of gas 0.088 g/cm3
Density of liquid 0.00708 g/cm3 
Density of solid 0.086 g/cm3
Electron configuration 1s1
Lower explosive limit  4% 
Upper explosive limit  75% 
Oxidation states  -1 and +1 
Critical temperature  -240.18 ºC 
Critical pressure  12.76 atm 
Critical volume  65 cm3/mo 
Velocity of sound  1,269.5 m/sec at 0 ºC 
Diffusion coefficient in air  0.634 cm2/sec at 0 ºC

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