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Hydrogen is a chemical element in the periodic table that has the symbol H and atomic number 1.

Notable Characteristics

Etymology: The name hydrogen, which comes from the French, in fact means water-maker, ultimately from the Greek hudôr (water) and gennen (generate).

At standard temperature and pressure conditions, hydrogen forms a diatomic gas, H₂, with a boiling point of only 20.27 K and a melting point of 14.02 K. Under exceedingly high pressures, like those found at the center of gas giants, the molecules lose their identity and the hydrogen becomes a liquid metal. Under the exceedingly low pressure conditions found in space, hydrogen tends to exist as individual atoms, simply because there is no way for them to combine; clouds of H₂ form and are associated with star formation.

Applications

Large quantities of hydrogen are needed industrially, notably in the Haber process for the production of ammonia, the hydrogenation of fats and oils, and the production of methanol. Other industrial processes include hydrodealkylation, hydrodesulfurization, and hydrocracking. Other industrial uses include the manufacture of hydrochloric acid, welding, rocket fuels, the reduction of metallic ores.

Hydrogen has been used as a lifting agent in balloons and zeppelins.

Hydrogen can be burned in internal combustion engines, and a fleet of hydrogen burning cars is maintained by Chrysler-BMW. Hydrogen fuel cells are being looked into as a way to provide potentially cheap, pollution free power.

Deuterium is used in nuclear applications as a moderator to slow down neutrons. Tritium is used as an isotopic label in biochemistry, as a radiation source in luminous paints, and in making hydrogen bombs.

History

Occurrence

Hydrogen is the most abundant element in the universe, making up around 75% of normal matter. Hydrogen is the lightest chemical element; its atoms consist of a single proton and electron. The most common isotope has no neutrons, although there are two others - deuterium with one, and radioactive tritium with two neutrons.

Compounds

Hydrogen has an electronegativity of 2.2, so it forms compounds where it is the more non-metallic and where it is the more metallic element. The former are called hydrides, where hydrogen either exists as H ions or just as a solute within the other element (as in Palladium hydride). The latter tend to be covalent, since the H ion would be a bare nucleus and so has a strong tendency to pull electrons to itself. Thus even in an acidic solution one sees ions like H₃O as the protons latch on to something.

Hydrogen combines with oxygen to form water, H₂O, and releases a lot of energy in doing so, burning explosively in air.

Isotopes

Hydrogen has two stable isotopes: protium with one proton and no neutrons (H) and deuterium with one proton and one neutron (H, D). Deuterium comprises 0.0184-0.0082% of all hydrogen (IUPAC); ratios of deuterium to protium are reported relative to the VSMOW standard reference water. A radioactive isotope, tritium (T or H) is another isotope and has one proton and two neutrons.

Precautions

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External Links

• WebElements.com - Hydrogen
• EnvironmentalChemistry.com - Hydrogen

External links used only for conversion (please delete before pasting into main article)

• Los Alamos National Laboratory - Hydrogen
  
• USGS Hydrogen Statistics and Information
  

See also:
Periodic Table, hydrogen bond, hydrogen atom, Antihydrogen