Covalent Bonding in Interstitial Monocarbides

As opposed to ionic bonding which involves electron transfer, covalent bonding means the sharing of electrons. Interstitial carbides have some degree of covalent bonding (M-C and M-M) resulting mostly from interaction between the Ip state of the carbon (see Ch. 2, Sec. 3.1) and the d state of the metal (the unfilled d orbitals mentioned in Sec. 2.2), and also from interaction between metal atoms. 

In order to form a monocarbide, the valence electrons of the carbon atom hybridize with the spd band of the metal atom. It is likely that the metal orbitals are the dP-sj hybridization since the typical octahedral grouping of the metal atoms centered on the carbon atom has six bonds to the six comers of the octahedron, thus favoring the M-C bond. Indeed, the cP-sjP hybridization is common in the Group IV metals (Ti, Zr, 

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