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| '''Hydrogen''' is a ] in the ] that has the symbol H and ] 1. | '''Hydrogen''' is a ] in the ] that has the symbol H and ] 1. | ||
| Hydrogen is the most ] element in the universe, making up around 75% of normal matter. Hydrogen is the lightest chemical element; its atoms consist of a single ] and ]. The most common ] has no ]s, although there are |
Hydrogen is the most ] element in the universe, making up around 75% of normal matter. Hydrogen is the lightest chemical element; its atoms consist of a single ] and ]. The most common ] has no ]s, although there are two others - ] with one, and radioactive ] with two neutrons. | ||
| At ] conditions, hydrogen forms a ] ], H<font size="-1"><sub>2</sub></font>, with a boiling point of only 20.28 ] and a melting point of 13.81 K. Under exceedingly high pressures, like those found at the center of ], the molecules lose their identity and the hydrogen becomes a liquid ]. 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 H<font size="-1"><sub>2</sub></font> form and are associated with ]. | At ] conditions, hydrogen forms a ] ], H<font size="-1"><sub>2</sub></font>, with a boiling point of only 20.28 ] and a melting point of 13.81 K. Under exceedingly high pressures, like those found at the center of ], the molecules lose their identity and the hydrogen becomes a liquid ]. 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 H<font size="-1"><sub>2</sub></font> form and are associated with ]. | ||
Revision as of 19:39, 11 March 2002
Hydrogen is a chemical element in the periodic table that has the symbol H and atomic number 1.
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.
At standard temperature and pressure conditions, hydrogen forms a diatomic gas, H2, with a boiling point of only 20.28 K and a melting point of 13.81 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.
Hydrogen has an electronegativity of 2.1, 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. The name hydrogen, which comes from the French, in fact means water-maker, ultimately from the Greek.
Isotopes
Hydrogen has two stable isotopes: protium with one proton and no neutrons (H) and deuterium with one protron 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.
External Link:
Los Alamos National Laboratory - Hydrogen
See also:
Periodic Table
hydrogen bond