Hydrogen halides
Hydrogen halides are chemical compounds that are formed from the corresponding halogens with hydrogen . The general empirical formula is HX, where X stands for the halogen. Their aqueous solutions are called hydrohalic acids . However, the common names hydrochloric acid for hydrochloric acid and hydrofluoric acid for hydrofluoric acid are much more familiar. Since the chemical properties of Tenness are completely unknown, the Tenness hydrogen is still unknown.
properties
Physical Properties
Except for hydrogen fluoride, all hydrogen halides are colorless, pungent-smelling gases under standard conditions. Their boiling and melting temperatures increase as the atomic number of the halogen increases. An exception is hydrogen fluoride , which deviates significantly from this tendency due to strong intermolecular interactions through hydrogen bonds . While hydrogen fluoride occurs as a hexamer even in the gaseous state , all other hydrogen halides are monomeric. The enthalpies of dissociation of the HX bond increase, the bond lengths decrease with decreasing atomic number.
Chemical properties
Hydrogen halides are classic Brønsted : You dissociate in aqueous solution in halide - anions (X - ) and protons ; the latter are present as hydrated oxonium cations (H 3 O + ), but are usually referred to simply as H + . The pK s values of hydrogen halides fall with growing period of the halogen sharply, which has experienced a particularly strong jump between the hydrofluoric and hydrochloric acid. The former is just a weak acid. The acid strength increases with decreasing dissociation enthalpy and not, as would be expected, with the increasing electronegativity of the halogen. Another noticeable trend is the increase in the reducing power of hydrogen halides and acids with increasing atomic number. In fact, hydrogen iodide (acid) is also used as a reducing agent. Hydrogen halides react with amines to form hydrohalides .
| connection | Melting temperature | Boiling temperature | Bond length | Enthalpy of dissociation | pK s value |
|---|---|---|---|---|---|
| Hydrogen fluoride (HF) | - 83.4 ° C | 19.5 ° C | 0.917 Å | 574 kJ / mol | 3.19 |
| Hydrogen chloride (HCl) | −114.0 ° C | −85.0 ° C | 1.274 Å | 428 kJ / mol | −6.1 |
| Hydrogen bromide (HBr) | - 82.8 ° C | −66.7 ° C | 1.414 Å | 362 kJ / mol | −8.9 |
| Hydrogen iodide (HI) | - 50.8 ° C | −35.4 ° C | 1.609 Å | 294 kJ / mol | −9.3 |
More detailed information on properties, use, safety instructions, etc. can be found under the specific hydrogen halides or their aqueous solutions, which are named hydrofluoric acid , hydrochloric acid , hydrobromic acid or hydroiodic acid .
Astatic hydrogen
Astatine occurs as a radioactive, especially very short-lived intermediate link of decay series and therefore only occurs in negligible amounts in nature. Accordingly, the level of knowledge about the chemical and physical properties of astatine and consequently of astatine hydrogen is limited. All that is known is that the reducing power of the latter is greater than that of hydrogen iodide, which, as expected, confirms the group trend.
literature
- Riedel, Janiak: Inorganische Chemie , 7th edition, de Gruyter, Berlin 2007, p. 409 ff., ISBN 978-3-11-018903-2 .