Hydride

When hydrides are called compounds of hydrogen with other elements. These can be divided into four types:

  • Covalent hydrides
  • Salt -like hydrides
  • Metallic hydrides
  • Complex Übergangsmetallhydride

It is important to note that here a sharp distinction ( in covalent, salt type, ...) is not possible to change because the bonding is not abrupt, but steadily. Different textbooks draw the dividing lines also different.

Covalent hydrides

This is a hydrogen compounds with the metalloids and non- metals of the 3rd - 7th Main group. Under normal conditions, it is usually gases or liquids. The most important group of these compounds are the hydrocarbons. The polarity of the bond in this case depends on the binding partners, there are

  • Compounds positiviertem hydrogen, in which the hydrogen has the oxidation number 1. Examples are water (H2O ), ammonia ( NH3) or hydrogen chloride (HCl). Here, the hydrogen has an acid function, and acts as an oxidant.
  • Compounds negativiertem hydrogen, in which the hydrogen has the oxidation number -1. In covalent compounds, these are to be regarded rather as special cases. Examples are silanes or boranes. Here, the hydrogen has a basic function and acts as a reducing agent.
  • Compounds containing a weakly polar hydrogen bonding. Important here, the carbon -hydrogen bonds of the hydrocarbons, which are considered non-polar. Again, the hydrogen is replaced by the oxidation number of 1.

Salt -like hydrides

Saline hydrides are ionic compounds which contain the H- hydride ion. Involved here are highly electropositive metals of the first and second main group, with the exception of beryllium. They crystallize in an ionic lattice. Examples: sodium hydride ( NaH) or calcium hydride ( CaH 2 ). With water or acids is carried out extremely violent evolution of hydrogen. The reducing action of the hydride is marked only at high temperatures, otherwise it acts as a very strong base.

Complex hydrides

They are also constructed in salt form, but in contrast to the salt-like hydrides contain no free hydride ions, but covalently bonded to a metal or semi-metal hydrogen. The best known and most important are here lithium aluminum hydride ( LiAlH4, lithium tetrahydridoaluminate, lithium aluminum hydride ) and sodium borohydride ( NaBH4, sodium borohydride, sodium borohydride ). They are used as a strong reducing agent in chemical synthesis because they can transfer the hydrogen as hydride ion to suitable substrates. While lithium aluminum hydride reacts explosively with water, sodium borohydride can be used in aqueous solution ( in other protic releasing agents such as alcohols and ).

Metallic hydrides

In these, the hydrogen stored in the metal lattice of transition metals. Mostly, these are not stoichiometric composition. The storage changing the structure of the metal mesh, and thus also of the same electronic properties. Examples of stoichiometric structures:

  • In the NiAs structure crystallize: MnH, CrH
  • In the fluorite structure crystallize: TiH2, VH2, CRH2 and CeH2

Complex Übergangsmetallhydride

The complex Übergangsmetallhydride are ternary compounds, which are composed of hydride, a transition metal (M) and an electro- positive metal (A). They have the general form AxMyHz. There are a large number of these compounds, but generally they are divided into alkaline earth and alkali - Übergangsmetallhydride Übergangsmetallhydride. They crystallize in a crystal lattice containing complex anions. Example: Mg2NiH4.

Ionic crystal
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