Hydrogen anion

Hydrogen anion

Names
Systematic IUPAC name Hydride
Identifiers
CAS Number	12184-88-2
ChEBI	CHEBI:29239
ChemSpider	145831 Y
Gmelin Reference	14911
Jmol 3D model	Interactive image
PubChem	166653
InChI InChI=1S/H/q-1 Y Key: KLGZELKXQMTEMM-UHFFFAOYSA-N Y
SMILES [H-]
Properties
Chemical formula	H−
Molar mass	1.01 g·mol−1
Thermochemistry
Std molar entropy (So298)	108.96 J K−1 mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

The hydrogen anion is a negative ion of hydrogen, H⁻. The hydrogen anion is an important constituent of the atmosphere of stars, such as the Sun. In chemistry, this ion is called hydride. The ion has two electrons bound by the electromagnetic force to a nucleus containing one proton.

Occurrence

The hydrogen anion is the dominant absorber of photons in the interstellar medium. It absorbs energies in the range 0.75–4.0 eV, which ranges from the infrared into the visible spectrum (Rau 1999, Srinivasan 1999). It also occurs in the Earth's ionosphere (Rau 1999).

Its existence was first proven theoretically by Hans Bethe in 1929 (Bethe 1929). H⁻ is unusual because, in its free form, it has no bound excited states, as was finally proven in 1977 (Hill 1977). It has been studied experimentally using particle accelerators (Bryant 1977).

In chemistry, the hydride anion is hydrogen that has the oxidation state −1. Hydride compounds formally contain a hydrogen anion. Most such compounds are in fact rather covalent. An example of a hydride is borohydride (BH⁻
₄).

See also

• Hydron (hydrogen cation)
• Electride, another very simple anion
• Hydrogen ion