Types of carbides

Types of carbides
Ionic salts

Salt like carbides are formed by the metals of[1]

* group 1 (the alkali metals )
* group 2 (the alkaline earths )
* group 3 (scandium, yttrium and lanthanum)
* group 11(copper, silver and gold)
* group 12 (zinc ,cadmium and mercury)
* only aluminium from group 13, (gallium, indium and thallium do not appear to form carbides).
* lanthanides when forming MC2 and M2C3 carbides
* actinides when forming MC2 and M2C3 carbides

Most commonly they are salts of C22− and are called acetylides, ethynides, acetylenediides or very rarely, percarbides.
Some compounds contain other anionic species:[1]

* C4−, sometimes called methanides (or methides) because they hydrolyse to give methane gas.
* C34− ion, sometimes called sesquicarbides, they hydrolyse to give methylacetylene.

The naming of ionic carbides is not consistent and can be quite confusing.

Acetylides

The polyatomic ion C22− contains a triple bond between the two carbon atoms. Examples are the carbides of the alkali metals e.g. Na2C2, some alkaline earths, e.g. CaC2 and lanthanoids e.g. LaC2.[1] The C-C bond distance ranges from 109.2pm in CaC2 (similar to ethyne), to 130.3 pm in LaC2 and 134pm in UC2.[1] The bonding in LaC2 has been described in terms of LaIII with the extra electron delocalised into the antibonding orbital on C22−, explaining the metallic conduction