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| A ], in the ] hydrogen has the symbol H and |
A ], in the ] hydrogen has the symbol H and ] 1. | ||
| The lightest |
The lightest chemical element and the most ] in the universe, around 75% of normal matter, consisting of a single ] and ]. The most common ] has no ]s, although there are two others - ] with one, and radioactive ] with two. | ||
| At normal STP-like conditions, hydrogen forms a ] ], H<sub>2</sub>, 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 ], 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 H<sub>2</sub> form and are associated with star formation. | At normal STP-like conditions, hydrogen forms a ] ], H<sub>2</sub>, 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<sub>2</sub> form and are associated with ]. | ||
| 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<sup>-</sup> ions or just as a solute within the other element (as in Palladium hydride). The latter tend to be covalent, since the H<sup>+</sup> ion would be a bare nucleus and so has a strong tendency to pull electrons to itself. Thus even in an |
Hydrogen has an ] 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<sup>-</sup> ions or just as a solute within the other element (as in ] hydride). The latter tend to be ], since the H<sup>+</sup> ion would be a bare nucleus and so has a strong tendency to pull electrons to itself. Thus even in an ]ic solution one sees ions like H<sub>3</sub>O<sup>+</sup> as the protons latch on to something. | ||
| Hydrogen combines with oxygen to form ], H<sub>2</sub>O, 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 ]. | Hydrogen combines with oxygen to form ], H<sub>2</sub>O, 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 ]. | ||
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| See: ] | |||
Revision as of 10:33, 25 December 2001
A chemical element, in the periodic table hydrogen has the symbol H and atomic number 1.
The lightest chemical element and the most abundant in the universe, around 75% of normal matter, consisting 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.
At normal STP-like 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.