Hydrogen

Basic features

Hydrogen is the lightest chemical element; its most common isotope comprises just one negatively charged electron, distributed around a positively charged proton (the nucleus of the atom). The electron is bound to the proton by the Coulomb force, the electrical force that one stationary, electrically charged nanoparticle exerts on another. The hydrogen atom has special significance in quantum mechanics as a simple physical system for which there is an exact solution to the Schrödinger equation; from that equation, the experimentally observed frequencies and intensities of the hydrogen's spectral lines can be calculated. Spectral lines are dark or bright lines in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies.

Related Topics:
Isotope - Electron - Proton - Nucleus - Coulomb force - Quantum mechanics - Schrödinger equation - Spectral line

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At standard temperature and pressure, hydrogen forms a diatomic gas, H2, with a boiling point of only 20.27 K and a melting point of 14.02 K.{{ref|commonsensescience.org}} Under extreme pressures, such as those at the center of gas giants, the molecules lose their identity and the hydrogen becomes a liquid metal. Under the extremely low pressure in space?virtually a vacuum?the element tends to exist as individual atoms, simply because there is no way for them to combine. However, clouds of H2 and singular hydrogen atoms are said to form in H I and H II regions and are associated with star formation, however the existance of singular hydrogen atoms is disputed.. Hydrogen plays a vital role in powering stars through the proton–proton and carbon–nitrogen cycle. These are nuclear fusion processes, which release huge amounts of energy in stars and other hot celestial bodies as hydrogen atoms combine into helium atoms.

Related Topics:
Standard temperature and pressure - K - Gas giant - Liquid metal - H I - H II region - Star formation - Stars - Proton–proton - Carbon–nitrogen cycle - Nuclear fusion - Helium

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H2 is highly soluble in water, alcohol, and ether. It has a high capacity for adsorption, in which it is attached to and held to the surface of some substances. It is an odorless, tasteless, colorless, and highly flammable gas that burns at concentrations as low as 4%. It reacts violently with chlorine and fluorine, forming hydrohalic acids that can damage the lungs and other tissues. When mixed with oxygen, hydrogen explodes on ignition. A unique property of hydrogen is that its flame is completely invisible in air. This makes it difficult to tell if a leak is burning, and carries the added risk that it is easy to walk into a hydrogen fire inadvertently.

Related Topics:
Adsorption - Flammable - Chlorine - Fluorine - Hydrohalic acid - Lung - Tissue

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See also: hydrogen atom.

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