Several carbides are assumed to be salts of the acetylide anion  (also called percarbide, by analogy with peroxide), which has a triple bond between the two carbon atoms. Alkali metals, alkaline earth metals, and lanthanoid metals form acetylides, for example, sodium carbide NaC, calcium carbide CaC, and LaC. Lanthanides also form carbides (sesquicarbides, see below) with formula MC. Metals from group 11 also tend to form acetylides, such as copper(I) acetylide and silver acetylide. Carbides of the actinide elements, which have stoichiometry MC and MC, are also described as salt-like derivatives of .
The C–C triple bond length ranges from 119.2 pm in CaC (similar to ethyne), to 130.3 pm in LaC and 134 pm in UC. The bonding in LaC has been described in terms of La with the extra electron delocalised into the antibonding orbital on , explaining the metallic conduction.