Atomic Number: 1
Symbol: H
Atomic weight: 1.0079
Discovery: Cavendish, 1766. Hydrogen was prepared for many years before it was recognized as a distinct element.
Electron Configuration: 1s1
Word Origin: Greek: hydro, water; genes, forming Named by Lavoisier.
Isotopes: Protium (0 neutrons), Deuterium (1 neutron), and Tritium (2 neutrons)
Ground level: 2S1/2
Ionization potential: 13.5984 ev
Physical form: Colorless gas
Melting point: -259.2°C
Boiling point: -252.762°C
Critical temperature: -240.18°C
Density: 0.082 g/L
Specific heat: 14.304 J/g•K
Valence: 1
Properties: Hydrogen is the most abundant element in the universe. The heavier elements were made from hydrogen or from other elements that were made from hydrogen. Hydrogen is a colorless, odorless, combustible gas. Hydrogen gas 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. The ortho form cannot be prepared in the pure state. Since the two forms of hydrogen differ in energy, their physical properties also differ.
Uses: Hydrogen is important in the proton-proton reaction and carbon-nitrogen cycle. Liquid hydrogen is used in cryogenics and in the study of superconductivity. Great quantities are used for the fixation of nitrogen from the air in the Haber ammonia process. Hydrogen is use in welding, for the hydrogenation of fats and oils, in methanol production, in hydrodealkylation, hydrocracking, and hydrodesulfurization. Other applications include producing rocket fuel, filling balloons, making fuel cells, producing hydrochloric acid, and reducing metallic ores. Deuterium is used as a moderator to slow down neutrons and as a tracer. Tritium is used in the production of the hydrogen (fusion) bomb. Tritium is also used in making luminous paints and as a tracer.
Sources: Hydrogen occurs in the free state in volcanic gases and some natural gases. Hydrogen is prepared by steam on heated carbon, decomposition of certain hydrocarbons with heat, action of sodium or potassium hydroxide on aluminum electrolysis of water, or displacement from acids by certain metals.
References: Los Alamos National Laboratory (2001), Crescent Chemical Company (2001), Lange's Handbook of Chemistry (1952)
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