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Hydrogen Facts

Chemical & Physical Properties of Hydrogen

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This is a vial containing ultrapure hydrogen gas.

This is a vial containing ultrapure hydrogen gas. Hydrogen is a colorless gas that glows violet when ionized.

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Periodic Table of the Elements

Hydrogen Atomic Number: 1

Hydrogen Symbol: H

Hydrogen Atomic Weight: [1.00784; 1.00811]
Reference: IUPAC 2009

Hydrogen Discovery: Cavendish, 1766. Hydrogen was prepared for many years before it was recognized as a distinct element.

Hydrogen Electron Configuration: 1s1

Hydrogen Word Origin: Greek: hydro, water; genes, forming Named by Lavoisier.

Hydrogen 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

Hydrogen 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.

Hydrogen 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.

Hydrogen 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.

Other Hydrogen Facts: While about 75% of the universe's elemental mass is hydrogen, hydrogen is relatively rare on Earth. The most common isotope of hydrogen is protium, which has one proton, but no neutrons. Hydrogen gas is extremely flammable. It was associated with the famous explosion of the Hindenburg airship and is used as a fuel by the space shuttle main engine.

References: Los Alamos National Laboratory (2001), Crescent Chemical Company (2001), Lange's Handbook of Chemistry (1952) International Atomic Energy Agency ENSDF database (Oct 2010)

Quiz: Ready to test your hydrogen facts knowledge? Take the Hydrogen Facts Quiz.

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