| Hydrogen - H
CAS: 1333-74-0 Description: Tasteless, colorless, odorless gas Classification: Non-metal Date of Discovery: 1766 Discoverer: Henry Cavendish Name Origin: Greek hudôr, "water" and genes, "forming" |
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Atomic Number: 1
Number of Neutrons: 0 Atomic Mass: 1.00794(7) amu Melting Point: -259.34 °C Boiling Point: -252.87 °C Density (293 K): 0.08988 g/cm3 70.8 g/l (-253 °C, liquid) 70.6 g/l (-262 °C, solid) Atomic volume: 14.4 cm3/mol Electrical resistivity: 0.630 10-6/cm 
Thermal conductivity: 0.001815 W/cmK Enthalpy of atomization: 217.57 kJ/mol Enthalpy of vaporization: 0.44936 kJ/mol Enthalpy of fusion: 0.05868 kJ/mol Specific heat capacity: 14.304 J/gK |
Energy levels: 1
Electron configuration: 1s1 Crystal Structure: Hexagonal Atomic radius: 0.79 Å Covalent radius: 0.32 Å Oxidation States: +1, -1 Electronegativity, Pauling: 2.20 Electron affinity: 0.754195 eV First ionization energy: 13.598 eV Polarizability: 0.666793 10-24cm3 |
| Isotope | Natural Abundance (%) | Atomic Mass | Half-life | Decay Mode | Spin |
| 1H | 99.985(1) | 1.007825032 | Stable | 1/2+ | |
| 2H | 0.015(1) | 2.014101778 | Stable | 1+ | |
| 3H | 3.01604927 | 12.32 y |  - |
1/2+ | |
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Hydrogen was prepared many years before it was recognized as a distinct substance by Cavendish in 1766. It was named by Lavoisier. Hydrogen is the most abundant of all elements in the universe, and it is thought that the heavier elements were, and still are, being built from hydrogen and helium. It has been estimated that hydrogen makes up more than 90% of all the atoms or three quarters of the mass of the universe. It is found in the sun and most stars, and plays an important part in the proton-proton reaction and
carbon-nitrogen cycle, which accounts for the energy of the sun and stars. It is thought that hydrogen is a major component of the planet Jupiter and that at some depth in the planet's interior the pressure is so great that solid molecular hydrogen is converted into solid metallic hydrogen. In 1973, it was reported that a group of Russian
experimenters may have produced metallic hydrogen at a pressure of 2.8 Mbar. At the transition the density changed from 1.08 to 1.3 g/cu cm. Earlier, in 1972, a Livermore (California) group also reported on a similar experiment in which they observed a pressure-volume point centered at 2 Mbar. It has been predicted that metallic hydrogen may be metastable; others have predicted it would be a superconductor at room temperature. On earth, hydrogen occurs chiefly in combination with oxygen in water, but it is also present in organic matter such as living plants, petroleum, coal, etc. It is present as the free element in the atmosphere, but only to the extent of less than 1 ppm by volume. It is the lightest of all gases, and combines with other elements, sometimes
explosively, to form compounds. Great quantities of hydrogen are required commercially for the fixation of nitrogen from the air in the Haber ammonia process and for the hydrogenation of fats and oils. It is also used in large quantities in methanol production, in hydrodealkylation, hydrocracking, and hydrodesulfurization. It is also
used as a rocket fuel, for welding, for production of hydrochloric acid, for the reduction of metallic ores, and for filling balloons. The lifting power of 1 cu. ft. of hydrogen gas is about 0.076 lb at 0 °C, 760 mm pressure. Production of hydrogen in the U.S. alone now amounts to about 3 billion cubic feet per year. It is prepared by the action of steam on heated carbon, by decomposition of certain hydrocarbons with heat, by the electrolysis of water, or by the displacement from acids by certain metals. It is also produced by the action of sodium or potassium hydroxide on aluminum. Liquid hydrogen is important in cryogenics and in the study of superconductivity, as its melting point is only a 20 degrees above absolute zero. The ordinary isotope of hydrogen, 1H, is known as protium. In 1932, Urey announced the discovery of a stable isotope, deuterium (2H or D) with an atomic weioht of 2. Deuterium is present in natural hydrogen to the extent of 0.015%. Two years later an unstable isotope, tritium (3H), with an atomic weight of 3 was discovered. Tritium has a half-life of about 12.5 years. Tritium atoms are also present in hydrogen but in much smaller proportion. Tritium is readily produced in nuclear reactors and is used in the production of the hydrogen bomb. It is also used as a radioactive agent in making luminous paints, and as a tracer. Deuterium gas is readily available, without permit, at about $1/l. Heavy water, deuterium oxide (D2O), which is used as a moderator to slow down neutrons, is available without permit at a cost of 6¢ to $1/g, depending on quantity and purity. Quite apart from isotopes, it has been shown that hydrogen gas under ordinary conditions is a mixture of two kinds of molecules,
known as ortho- and para-hydrogen, which differ from one another by
the spins of their electrons and nuclei. Normal hydrogen at room temperature contains 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 differ in energy, the physical properties also differ. The melting and boiling points of parahydrogen are about 0.1 °C lower than those of normal hydrogen. Consideration is being given to an entire economy based on solar- and nuclear-generated hydrogen. Located in remote regions, power plants would electrolyze sea waters, the hydrogen produced would travel to distant cities by pipelines. Pollution-free hydrogen could replace natural gas, gasoline, etc., and could serve as a reducing agent in metallurgy, chemical processing, refining, etc. It could also be used to convert trash into methane and ethylene. Public acceptance, high capital investment, and the high
present cost of hydrogen with respect to present fuels are but a few of the problems facing establishment of such an economy.
LINKS: American Hydrogen Association Chemical of the Week - Hydrogen Hydrogen Gas Molecule Hydrogen Peroxide Online National Hydrogen Association Return
Sources for the information on this website include: Lide, David R., ed. CRC Handbook of Chemistry and Physics, 78th Ed., 1997-1998. |
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