hydrogen
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| hydrogen | |
|---|---|
| Name | hydrogen |
| Category | nonmetal |
| Standard atomic weight | 1.008 |
| Electron configuration | 1s¹ |
| Phase at STP | gas |
| Melting point K | 13.99 |
| Boiling point K | 20.271 |
| Density at STP gpcm3 | 0.08988 |
| Triple point K | 13.8033 |
| Critical point K | 32.938 |
hydrogen. It is the lightest and most abundant chemical element in the universe, constituting roughly 75% of its elemental mass. As the primary component of stars like the Sun, it fuels nuclear fusion reactions that release immense energy. On Earth, it is predominantly found in compounds such as water and hydrocarbons, playing a fundamental role in chemistry and biology.
Properties
Under standard conditions, it exists as a diatomic gas (H₂) that is colorless, odorless, and highly flammable. It exhibits the lowest atomic number and atomic mass of all elements, with its most common isotope, protium, possessing a single proton and no neutron. The element displays unique quantum mechanical behavior due to its simple atomic structure, which was pivotal in the development of quantum theory. Its other isotopes include deuterium, a stable isotope used in nuclear magnetic resonance spectroscopy, and radioactive tritium, employed in luminous paint and as a tracer in biochemistry. At extremely high pressures, such as those found within gas giant planets like Jupiter, it is predicted to exist in a metallic hydrogen state.
Occurrence and production
In the cosmos, vast molecular clouds of H₂ within galaxies like the Milky Way are the birthplaces of new stars. On our planet, it is rarely found in its free form and must be extracted from compounds. The primary industrial method is steam reforming of natural gas, a process developed by companies like BASF. Electrolysis of water, using electricity to split water molecules, offers a cleaner route, especially when powered by renewable energy sources such as solar power from facilities like the Ivanpah Solar Power Facility. Significant quantities are also produced as a byproduct of chlor-alkali process operations in the chemical industry.
Compounds
It forms an immense variety of compounds, most notably water (H₂O), which is essential for all known life forms. With carbon, it creates a vast array of hydrocarbons, the primary constituents of fossil fuels like petroleum and natural gas. In acid–base reactions, it is the defining component of Brønsted–Lowry acids, which donate protons in aqueous solution. Important inorganic compounds include ammonia (NH₃), crucial for the Haber process and fertilizer production, and hydrogen chloride (HCl), a key industrial acid. In organic chemistry, it is a component of all biomolecules, including carbohydrates, proteins, and nucleic acids like DNA.
Applications
The largest single use is in the Haber–Bosch process for synthesizing ammonia, a cornerstone of modern agriculture pioneered by Fritz Haber and Carl Bosch. It is a critical reagent in hydrocracking and hydrodesulfurization to refine petroleum at facilities like those operated by ExxonMobil. As a potential clean energy carrier, it is used in fuel cells to power vehicles, such as the Toyota Mirai, and provides rocket propellant for space agencies like NASA and SpaceX. The gas is also employed to create a protective reducing atmosphere in metallurgy for annealing metals and in the production of methanol via the MTG process.
Safety and precautions
As a highly flammable gas, it forms explosive mixtures with air across a wide range of concentrations, a hazard famously demonstrated by the Hindenburg disaster. Leaks can be difficult to detect without specialized sensors due to its odorless and colorless nature. When handled in cryogenic liquid form, it poses significant risks of cryogenic burn and pressure vessel rupture. Safety protocols in industries and laboratories are governed by organizations like the National Fire Protection Association and regulations such as those from the Occupational Safety and Health Administration. In confined spaces, it can act as an asphyxiant by displacing oxygen.
History
The combustible nature of gas mixtures containing it was observed in the 16th and 17th centuries by alchemists including Paracelsus. It was first identified as a distinct substance in 1766 by Henry Cavendish, who called it "inflammable air" and later determined it produced water when burned, a key finding in the demise of the phlogiston theory. Antoine Lavoisier named it "hydrogen," meaning "water-former," following his experiments which helped establish modern chemistry. Its atomic structure became central to Niels Bohr's model of the atom and the development of quantum mechanics by scientists like Erwin Schrödinger. The discovery of its isotopes, deuterium by Harold Urey and tritium by Ernest Rutherford, further expanded nuclear science.