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Oxidation & Electrons | Appearance & Characteristics Reactions | Compounds | Radius | Conductivity Abundance & Isotopes 
Nasa image: Vast Quantities of Hydrogen in Remote Galaxies |
General:
| Name: Hydrogen | Symbol: H |
| Type: Non-Metal | Atomic weight: 1.0079 |
| Density @ 293 K: 0.0000899 g/cm3 | Atomic volume: 14.4 cm3/mol |
| Discovered: Although it had been made previously by others, hydrogen was first recognized as a distinct element by Henry Cavendish in 1766 when he prepared it by adding strong acids to metals. He described hydgrogen as "inflammable air from metals". Cavendish also observed that when the substance was burned, it produced water. Lavoisier later named the element hydrogen (1783). The name comes from the Greek 'hydro' meaning water and 'genes' meaning forming. | |
States
| State (s, l, g): gas | |
| Melting point: 14.01 K (-259.14 oC) | Boiling point: 20.28 K (-252.87 oC) |
Energies
| Specific heat capacity: 14.304 J g-1 K-1 | Heat of atomization: 218 kJ mol-1 |
| Heat of fusion: 0.117 kJ mol-1 of H2 | Heat of vaporization (sublimation): 0.904 kJ mol-1 of H2 |
| 1st ionization energy: 1312 kJ mol-1 | 2nd ionization energy: kJ mol-1 |
| 3rd ionization energy: kJ mol-1 | Electron affinity: 72.7711 kJ mol-1 |
Oxidation & Electrons
| Shells: 1 | Electron configuration: 1s1 |
| Minimum oxidation number: -1 | Maximum oxidation number: 1 |
| Min. common oxidation no.: -1 | Max. common oxidation no.: 1 |
| Electronegativity (Pauling Scale): 2.18 | Polarizability volume: 0.7 Å3 |
Appearance & Characteristics
| Structure: hcp: hexagonal close packed (as solid at low temperatures) | Color: Colorless |
| Harmful effects: Hydrogen is highly flammable and has an almost invisible flame, which can lead to accidental burns. | Hardness: mohs |
| Characteristics: Hydrogen is the simplest element of all, and the lightest. It is also by far the most common element in the Universe. Over 90 percent of the atoms in the Universe are hydrogen. In its commonest form, the hydrogen atom is made of one proton, one electron, and no neutrons. Hydrogen is the only element that can exist without neutrons. Hydrogen is a colorless, odorless gas which exists, at standard temperature and pressure, as diatomic molecules, H2. It burns and forms explosive mixtures in air and it reacts violently with oxidants. On Earth, the major location of hydrogen is in water, H2O. There is little free hydrogen on Earth because it is so light it escapes from the atmosphere into space. | |
Nasa: The Space Shuttle's external fuel tank (orange) filled with liquid hydrogen and oxygen. 
Hydrogen cars emit water rather than pollutants. |
Uses: Large quantities of hydrogen are used in the Haber process (production of ammonia), hydrogenation of fats and oils, methanol production, hydrocracking, and hydrodesulfurization. Hydrogen is also used in metal refining. Liquid hydrogen is used as a rocket fuel, for example powering the Space Shuttle's lift-off and ascent into orbit. Liquid hydrogen and oxygen are held in the Shuttle's large, external fuel tank. (See image left.) Hydrogen's two heavier isotopes (deuterium and tritium) are used in nuclear fusion. The hydrogen economy has been proposed as a replacement for our current hydrocarbon (oil and coal based) economy. The basis of the hydrogen economy is that energy is produced when hydrogen combusts with oxygen and the only by-product from the reaction is water. At the moment, however, the hydrogen for hydrogen-powered cars is produced from hydrocarbons. Only when solar or wind energies, for example, can be used commercially to split water into hydrogen and oxygen will a true hydrogen economy be possible. |
Reactions
| Reaction with air: vigorous, ⇒ H2O | Reaction with 6 M HCl: none |
| Reaction with 15 M HNO3: none | Reaction with 6 M NaOH: none |
Compounds
| Oxide(s): H2O | Chloride(s): HCl |
| Hydride(s): H2 |
Radius
| Atomic radius: 25 pm | Ionic radius (1+ ion): pm |
| Ionic radius (2+ ion): pm | Ionic radius (3+ ion): pm |
| Ionic radius (2- ion): pm | Ionic radius (1- ion): pm |
Conductivity
| Thermal conductivity: 0.1805 W m-1 K-1 | Electrical conductivity: S cm-1 |
Abundance & Isotopes
Laboratory electrolysis of water. Electrical energy is used to split water. Hydrogen gathers in one test-tube, oxygen in the other. |
Abundance Earth's crust: 1,500 ppm by weight (0.15 %), 3.1 % by moles Abundance Solar System: 75 % by weight, 93 % by moles Cost, pure: 12 $/100g Cost, bulk: $/100g Source: Hydrogen is prepared commercially by reacting superheated steam with methane or carbon. In the laboratory, hydrogen can be produced by the action of acids on metals such as zinc, or by the electrolysis of water (shown on the left). Isotopes: Hydrogen has three isotopes, 1H (protium), 2H (deuterium) and 3H (tritium). Its two heavier isotopes (deuterium and tritium) are used for nuclear fusion. Protium is the most abundant isotope, and tritium the least abundant. Tritium is unstable with a half-life of about 12 years 4 months. |
