Hydrogen (H)

Science / Periodic Table of Elements / Hydrogen (H): Atomic number: 1, Atomic mass: 1.007825 g.mol -1, Electronegativity: 2.1, Density: 0.0899*10 -3 g.cm -3 at 20 °C, Melting point: - 259.2 °C, Boiling point: - 252.8 °C, Vanderwaals radius: 0.12 nm, Ionic radius: 0.208 (-1) nm, Isotopes: 3, Electronic shell: 1s1, Energy of first ionisation: 1311 kJ.mol -1, Discovered by: Henry Cavendish in 1766. First element in the periodic table. In normal conditions it’s a colourless, odourless and insipid gas, formed by diatomic molecules, H2. The hydrogen atom, symbol H, is formed by a nucleus with one unit of positive charge and one electron. Its atomic number is 1 and its atomic weight 1,00797 g/mol. It’s one of the main compounds of water and of all organic matter, and it’s widely spread not only in The Earth but also in the entire Universe. There are three hydrogen isotopes: protium, mass 1, found in more than 99,985% of the natural element; deuterium, mass 2, found in nature in 0.015% approximately, and tritium, mass 3, which appears in small quantities in nature, but can be artificially produced by various nuclear reactions. Uses: The most important use of hydrogen is the ammonia synthesis. The use of hydrogen is extending quickly in fuel refinement, like the breaking down by hydrogen (hydrocracking), and in sulphur elimination. Huge quantities of hydrogen are consumed in the catalytic hydrogenation of unsaturated vegetable oils to obtain solid fat. Hydrogenation is used in the manufacture of organic chemical products. Huge quantities of hydrogen are used as rocket fuels, in combination with oxygen or fluor, and as a rocket propellent propelled by nuclear energy. Hydrogen can be burned in internal combustion engines. Hydrogen fuel cells are being looked into as a way to provide power and research is being conducted on hydrogen as a possible major future fuel. For instance it can be converted to and from electricity from bio-fuels, from and into natural gas and diesel fuel, theoretically with no emissions of either CO2 or toxic chemicals. Properties: Common hydrogen has a molecular weight of 2,01594 g. As a gas it has a density of 0.071 g/l at 0??C and 1 atm. Its relative density, compared with that of the air, is 0.0695. Hydrogen is the most flammable of all the known substances. Hydrogen is slightly more soluble in organic solvents than in water. Many metals absorb hydrogen. Hydrogen absorption by steel can result in brittle steel, which leads to fails in the chemical process equipment. At normal temperature hydrogen is a not very reactive substance, unless it has been activated somehow; for instance, by an appropriate catalyser. At high temperatures it’s highly reactive. Although in general it’s diatomic, molecular hydrogen dissociates into free atoms at high temperatures. Atomic hydrogen is a powerful reductive agent, even at ambient temperature. It reacts with the oxides and chlorides of many metals, like silver, copper, lead, bismuth and mercury, to produce free metals. It reduces some salts to their metallic state, like nitrates, nitrites and sodium and potassium cyanide. It reacts with a number of elements, metals and non-metals, to produce hydrides, like NAH, KH, H2S and PH3. Atomic hydrogen produces hydrogen peroxide, H2O2, with oxygen. Atomic hydrogen reacts with organic compounds to form a complex mixture of products; with etilene, C2H4, for instance, the products are ethane, C2H6, and butane, C4H10. The heat released when the hydrogen atoms recombine to form the hydrogen molecules is used to obtain high temperatures in atomic hydrogen welding. Hydrogen reacts with oxygen to form water and this reaction is extraordinarily slow at ambient temperature; but if it’s accelerated by a catalyser, like platinum, or an electric spark, it’s made with explosive violence.

Hydrogen Peroxide

Entertainment / Photography / Hydrogen Peroxide: Chemical used in hypo clearing agents. MORE

Standard Hydrogen Electrode

Science / Chemistry / Standard Hydrogen Electrode: A platinum electrode that runs the half reaction 2 H+(aq, 1M) + 2 e- rightarrow H2(g, 1 atm), chosen as a reference for cell voltages. The electrode potential of the standard hydrogen electrode is def MORE

Hydrogen Bond

Science / Biology / Hydrogen Bond: A weak bond between two atoms (one of which is hydrogen) with partial but opposite electrical charges. MORE