Hydrogen
Hydrogen is a chemical element with chemical symbol H and atomic number 1. With an atomic weight of 1.00794 u, hydrogen is the lightest element on theperiodic table. Its monatomic form (H) is the most abundant chemical substance in the Universe, constituting roughly 75% of all baryonic mass.
Non-remnantstars are mainly composed of hydrogen in its plasma state. The most commonisotope of hydrogen, termed protium (name rarely used, symbol 1H), has one proton and no neutrons.
The universal emergence of atomic hydrogen first occurred during the recombination epoch. At standard temperature and pressure, hydrogen is acolorless, odorless, tasteless, non-toxic, nonmetallic, highly combustible diatomicgas with the molecular formula H2. Since hydrogen readily forms covalentcompounds with most non-metallic elements, most of the hydrogen on Earth exists in molecular forms such as in the form of water or organic compounds.
Hydrogen plays a particularly important role in acid–base reactions as many acid-base reactions involve the exchange of protons between soluble molecules. In ionic compounds, hydrogen can take the form of a negative charge (i.e., anion) when it is known as a hydride, or as a positively charged (i.e., cation) species denoted by the symbol H+. The hydrogen cation is written as though composed of a bare proton, but in reality, hydrogen cations in ionic compounds are always more complex species than that would suggest. As the only neutral atom for which theSchrödinger equation can be solved analytically,[10] study of the energetics and bonding of the hydrogen atom has played a key role in the development ofquantum mechanics.
Hydrogen gas was first artificially produced in the early 16th century, via the mixing of metals with acids. In 1766–81, Henry Cavendish was the first to recognize that hydrogen gas was a discrete substance,[11] and that it produces water when burned, a property which later gave it its name: in Greek, hydrogen means "water-former".
Industrial production is mainly from the steam reforming of natural gas, and less often from more energy-intensive hydrogen production methods like the electrolysis of water.[12] Most hydrogen is employed near its production site, with the two largest uses being fossil fuel processing (e.g., hydrocracking) andammonia production, mostly for the fertilizer market. Hydrogen is a concern inmetallurgy as it can embrittle many metals,[13] complicating the design of pipelines and storage tanks.[14]
Contents
- 1Properties
- 2History
- 3Natural occurrence
- 4Production
- 5Applications
- 6Biological reactions
- 7Safety and precautions
- 8Notes
- 9References
- 10Further reading
- 11External links
History
Discovery and use
Main article: Timeline of hydrogen technologies
In 1671, Robert Boyle discovered and described the reaction between iron filings and dilute acids, which results in the production of hydrogen gas.[59][60] In 1766, Henry Cavendish was the first to recognize hydrogen gas as a discrete substance, by naming the gas from a metal-acid reaction "flammable air". He speculated that "flammable air" was in fact identical to the hypothetical substance called "phlogiston"[61][62] and further finding in 1781 that the gas produces water when burned. He is usually given credit for its discovery as an element.[6][7] In 1783, Antoine Lavoisier gave the element the name hydrogen (from the Greek ὑδρο-hydro meaning "water" and -γενής genes meaning "creator")[8] when he and Laplace reproduced Cavendish's finding that water is produced when hydrogen is burned.[7]
[
Antoine-Laurent de Lavoisier
Lavoisier produced hydrogen for his experiments on mass conservation by reacting a flux of steam with metallic iron through an incandescent iron tube heated in a fire. Anaerobic oxidation of iron by the protons of water at high temperature can be schematically represented by the set of following reactions:
Fe + H2O → FeO + H22 Fe + 3 H2O → Fe2O3 + 3 H23 Fe + 4 H2O → Fe3O4 + 4 H2
Many metals such as zirconium undergo a similar reaction with water leading to the production of hydrogen.
Hydrogen was liquefied for the first time by James Dewar in 1898 by using regenerative coolingand his invention, the vacuum flask.[7] He produced solid hydrogen the next year.[7] Deuteriumwas discovered in December 1931 by Harold Urey, and tritium was prepared in 1934 by Ernest Rutherford, Mark Oliphant, and Paul Harteck.[6] Heavy water, which consists of deuterium in the place of regular hydrogen, was discovered by Urey's group in 1932.[7] François Isaac de Rivaz built the first de Rivaz engine, an internal combustion engine powered by a mixture of hydrogen and oxygen in 1806. Edward Daniel Clarke invented the hydrogen gas blowpipe in 1819. The Döbereiner's lamp and limelight were invented in 1823.[7]
The first hydrogen-filled balloon was invented by Jacques Charles in 1783.[7] Hydrogen provided the lift for the first reliable form of air-travel following the 1852 invention of the first hydrogen-lifted airship by Henri Giffard.[7] German count Ferdinand von Zeppelin promoted the idea of rigid airships lifted by hydrogen that later were called Zeppelins; the first of which had its maiden flight in 1900.[7] Regularly scheduled flights started in 1910 and by the outbreak of World War I in August 1914, they had carried 35,000 passengers without a serious incident. Hydrogen-lifted airships were used as observation platforms and bombers during the war.
The first non-stop transatlantic crossing was made by the British airship R34 in 1919. Regular passenger service resumed in the 1920s and the discovery of helium reserves in the United States promised increased safety, but the U.S. government refused to sell the gas for this purpose. Therefore, H2 was used in the *Hindenburg* airship, which was destroyed in a midair fire over New Jersey on 6 May 1937.[7] The incident was broadcast live on radio and filmed. Ignition of leaking hydrogen is widely assumed to be the cause, but later investigations pointed to the ignition of the aluminized fabric coating by static electricity. But the damage to hydrogen's reputation as a lifting gas was already done.
In the same year the first hydrogen-cooled turbogenerator went into service with gaseous hydrogen as a coolant in the rotor and the stator in 1937 at Dayton, Ohio, by the Dayton Power & Light Co.;[63] because of the thermal conductivity of hydrogen gas, this is the most common type in its field today.
The nickel hydrogen battery was used for the first time in 1977 aboard the U.S. Navy's Navigation technology satellite-2 (NTS-2).[64] For example, the ISS,[65] Mars Odyssey[66] and the Mars Global Surveyor[67] are equipped with nickel-hydrogen batteries. In the dark part of its orbit, the Hubble Space Telescope is also powered by nickel-hydrogen batteries, which were finally replaced in May 2009,[68] more than 19 years after launch, and 13 years over their design life.[69]...