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Contributing author Main contribution Organization
Karl Verfondern Chapter coordinator FZJ

Contributing reviewer Information reviewed Organization
Mike Kusnetsov Hydrogen Fundamentals FZK
Alexander Lelyakin Hydrogen Fundamentals FZK


Hydrogen is the first element in the periodic table with the atomic number 1. It is the lightest and most abundant element in the universe representing 75 mass% or 90 vol% of all matter. On Earth, it is mostly found in compounds with almost every other element. Considering just the compound water, the hydrogen contents bound in the total water supply of the world is on the order of 1014 t. Hydrogen exists also as a free element in the atmosphere, but only to the extent of less than 1 ppm (by volume). Free ionic hydrogen is more reactive than molecular hydrogen, the nonpolar-covalent compound of two hydrogen atoms. In 1776, Henry Cavendish identified hydrogen as a distinct species. It was given the name “water maker” by Antoine Lavoisier seven years later, who proved that water was composed of hydrogen and oxygen.

The most common hydrogen isotope is protium (H-1, H, atomic mass 1.007822). The second isotope is the stable deuterium (H-2, D) or heavy hydrogen discovered in 1932 by H. C. Urey and co-workers. Deuterium has a natural fraction of 0.014 % with physical and chemical properties slightly different from H-1. Nearly all D in natural hydrogen is in combination with hydrogen atoms, the diatomic HD with a fraction of 0.032 % in natural hydrogen; the existence of molecular D is highly improbable. Third hydrogen isotope is the radioactive tritium (H-3, T) with a half life of 12.3 years, discovered in 1934 by E. Rutherford. But also the short-lived isotopes H-4, H-5, and H-7 have been synthesised in the meantime.

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Page last modified on October 30, 2008, at 05:26 PM