HYDROGEN Laura Vidal Juan

INTRODUCTION Etymology: the name of an element. Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. Its atomic mass is amu (hydrogen is the lightest element). Hydrogen is the most abundant of the chemical elements, constituting roughly 75% of the universe's elemental mass Elemental hydrogen is relatively rare on Earth, and is industrially produced from hydrocarbons

DISCOVERY T. Von Hohenheim = Paracelsus (1493–1541) produced H 2 artificially via the mixing of metals with strong acids. Robert Boyle (1671) rediscovered and described the reaction between iron filings and dilute acids, which results in the production of hydrogen gas. Henry Cavendish (1766) recognized hydrogen gas as a discrete substance, by identifying the gas from a metal-acid reaction as "inflammable air" and further finding that the gas produces water when burned. Antoine Lavoisier (1783) gave the element the name of hydrogen when he (with Laplace) reproduced Cavendish's finding. Study of the energetics and bonding of the hydrogen atom by Maxwell, has played a key role in the development of quantum mechanics.

COMPOUNDS Bonded to fluorine, oxygen, or nitrogen it forms hydrogen bonding. With metals and metalloids it forms hydrides, that could be implied in coordination complex. With carbon it forms organic compounds: importance in Biochemistry. H+ is implied in acid-base chemistry.

BIOHYDROGEN H 2 is a product of some types of anaerobic metabolism and it is produced by several microorganisms. It take part in redox reactions (hydrogenases). H 2 is created during pyruvate fermentation to water. Water splitting, that occurs during photosintesis, give rise to H +. H + is important in the electronic transfer chain.

CHEMICAL CHARACTERISTICS Hydrogen is highly soluble in many compounds of rare earth metals and transition metals and can be dissolved in crystalline and amorphous metals. It is highly flammable and will burn at concentrations as low as 4% H 2 in air. It ignites automatically at a temperature of 560 °C. H 2 reacts directly with other oxidizing elements. Pure hydrogen-oxygen flames burn in the ultraviolet color range and are nearly invisible to the naked eye.

SOME PROPERTIES  General: At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas with the molecular formula H 2.  Physical properties:  Atomic properties: Crystal structure = hexagonal Atomic radius = 25 pm Electronegativity = 2.1 Heat of fusion = 117 kJ·mol −1 Heat of vaporization = kJ·mol −1 It has the highest thermal conductivity of any gas Density = g/L Melting point = K Boiling point = K

APPLICATIONS I One of the first uses of H 2 was for balloons, and later airships. Infamously, H 2 was used in the Hindenburg airship that was destroyed in a midair fire. The highly flammable hydrogen (H 2 ) was later replaced for airships and most balloons by the unreactive helium (He). Uses in petroleum and chemical industries: processing of fossil fuels, and in the production of ammonia. Uses as a reactant: hydrogenating agent (in increasing the level of saturation of unsaturated fats and oils ); in the production of methanol; in the manufacture of hydrochloric acid; reducing agent of metallic ores.

APPLICATIONS II Applications in physics and engineering: shielding gas in welding methods, the rotor coolant in electrical generators at power stations Liquid H 2 is used in cryogenic research As a tracer gas for minute leak detection Isotopes: Protium is the most common isotope; Deuterium (hydrogen-2) is used in nuclear fission application; Tritium (hydrogen-3), produced in nuclear reactors, is used in the production of hydrogen bombs, as an isotopic label in the biosciences, and as a radiation source in luminous paints.