Hydrogen halide

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Hydrogen halides (or hydrohalic acids) are inorganic compounds that contain a hydrogen ion and a halide ion. The halogens are fluorine, chlorine, bromine and iodine. Astatine does not make a stable hydrogen halide, so it is not included.

The hydrogen halides are diatomic molecules with no tendency to ionize in the gas phase. Chemists therefore distinguish hydrogen chloride from hydrochloric acid. The former is a gas at room temperature that reacts with water to give the acid. Once the acid has formed, the diatomic molecule can not easily be regenerated.

compound formula structure model d(H−X) / pm
(gas phase)
μ / D Notes
hydrogen fluoride
HF
Hydrogen-fluoride-2D-dimensions.png
Hydrogen-fluoride-3D-vdW.png
91.7
1.86
Highly toxic, weak acid
hydrogen chloride
HCl
Hydrogen-chloride-2D-dimensions.png
Hydrogen-chloride-3D-vdW.png
127.4
1.11
Strong acid, most common
hydrogen bromide
HBr
Hydrogen-bromide-2D-dimensions.png
Hydrogen-bromide-3D-vdW.png
141.4
0.788
Strong acid
hydrogen iodide
HI
Hydrogen-iodide-2D-dimensions.png
Hydrogen-iodide-3D-vdW.png
160.9
0.382
Strong acid, reducing agent