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Hydrogen - H General Information Discovery Hydrogen was first recognized as an element by Cavendish in 1766, and named by Lavoisier. Appearance Hydrogen is a colourless gas. Source Hydrogen is found in the sun and most of the stars, and is easily the most abundant element in the universe. The planet Jupiter is composed mostly of hydrogen, and there is a theory that in the interior of the planet the pressure is so great that metallic hydrogen is formed from solid molecular hydrogen. On this planet, hydrogen is found in the greatest quantities in water, but is present in the atmosphere only in small amounts - less than 1 part per million by volume. Hydrogen is prepared commercially by several methods; electrolysis of water, decomposition of hydrocarbons, displacement from acids by certain metals, action of steam on heated carbon, and action of sodium or potassium hydroxide on aluminium. Uses Large quantities are used in the Haber Process (the production of ammonia for agricultural use) and for the hydrogenation of oils to form fats. It has several other uses, including welding and the reduction of metallic ores, and liquid hydrogen is important in cryogenics and superconductivity studies as its melting point is just above absolute zero. Biological Role Hydrogen is the basis of all life, as part of the DNA molecule. General Information There are three isotopes of hydrogen - protium, deuterium and tritium. Protium is the ordinary isotope, with an atomic mass of 1. Deuterium, atomic mass 2, was discovered in 1932 and tritium, atomic mass 3, in 1934. Tritium is unstable, with a half-life of about 12.5 years, and is used in nuclear reactors, hydrogen bombs, luminous paints and as a tracer. Protium is the most abundant isotope, and tritium the least abundant. It would be possible to base the entire economy of the Earth on solar and nuclear generated hydrogen, an advantage as hydrogen itself is non-polluting, but the high cost of hydrogen compared with current hydrocarbon fuels makes this unrealistic at present. |
| Physical Information | |||
| Atomic Number | 1 | ||
| Relative Atomic Mass (12C=12.000) | 1.008 | ||
| Melting Point/K | 14 | ||
| Boiling Point/K | 20.3 | ||
| Density/kg m-3 | 0.090 (gas, 273K) | ||
| Ground State Electron Configuration | 1s1 | ||
| Electron Affinity(M-M-)/kJ mol-1 | -72.8 |
| Key Isotopes | ||||||
| nuclide | 1H | 2H | 3H | |||
| atomic mass | 1.008 | 2.014 | 3.016 | |||
| natural abundance | 99.99% | 0.015% | 0% | |||
| half-life | stable | stable | 12.262 yrs |
| Other Information | ||
| Enthalpy of Fusion/kJ mol-1 | 0.12 | |
| Enthalpy of Vaporisation/kJ mol-1 | 0.46 | |
| Oxidation States | ||
| main | H+1 | |
| others | H0, H-1 | |
| Covalent Bonds /kJ mol-1 | ||
| H - H | 454 | |
| H - F | 566 | |
| H - Cl | 431 | |
| H - Br | 366 | |
| H - I | 299 | |
| Ionisation Energies/kJ mol-1 | ||
| M - M+ | 1312 | |
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