Carbide

This article is about type of material. For specific material sometimes called "carbide", see tungsten carbide.

Carbide is a name for chemical compounds of carbon and a metal or mixture of metals. It can also refer to the major anions of carbon, C⁴⁻, C2−2, and C4−3.

Different carbides have different structures and chemical properties. Many are refractory materials, meaning they are strong even when very hot.

Types of carbide

Carbides are grouped by their main type of chemical bond.

Metal-like carbides

Carbides from the early transition metals are called metallic (metal-like) or interstitial carbides. "Interstitial" means that the small carbon atoms are inside the gaps between the big metal atoms. The carbide is metallic Some of the most important carbides, like tungsten carbide and titanium carbide, are metal-like carbides.

Salt-like carbides

Salt-like carbides are made by the alkali metals, alkaline earth metals, some lanthanides and actinides, the Group 3 metals (scandium, yttrium, and lutetium), and aluminium. These electropositive elements are good at giving away electrons, even though carbon is not normally good at taking electrons. These carbides are "salt-like" because they are ionic compounds.

Salt-like carbides can be grouped according to the structure of the carbon anion. These anions are strong bases that react with water to make hydrocarbons. The anions are named based on the hydrocarbon made by this reaction:

Anion		Hydrocarbon		Example
Methanide	C4−	Methane	CH4	Aluminium carbide	Al4C3
Acetylide	C2−2	Acetylene	C2H2	Calcium carbide	CaC2
Allylide	C4−3	Allylene	C3H4	Magnesium carbide	Mg2C3

The names for these carbides are not systematic names. The systematic name "methanide" would refer to the CH−3 anion, not C⁴⁻. This "methanide" is too unstable to exist normally. Compounds like methyllithium have covalent bonds with a methyl group, not ionic bonds to CH−3.

Covalent carbides

Most chemical bonds with carbon are covalent bonds, including carbides. The covalent carbides aren't "carbides with covalent bonds", but "carbides with mostly or only covalent bonds". The two covalent carbides are silicon carbide and boron carbide. This is because silicon and boron have similar size and electronegativity to carbon.