Formation of methane (CH4) molecule on the basis of electronic theory of valence is described below. The electronic configuration of carbon is K, L: 2, 4. Thus, there are four electrons in the valence shell of carbon atom. To complete its octet, it needs four more electrons. A carbon atom completes its octet by sharing of electrons. Each hydrogen atom has only one electron in its valence shell, (K-shell. Thus, to complete its K-shell, a hydrogen atom requires one more electron (K-shell can have only two electrons). Thus, one carbon atom shares its four outermost electrons with four electrons of four hydrogen atoms.
The bond formed due top the sharing of one electron pair is called a single covalent bond. Thus, the carbon atom in methane forms four single bonds with four hydrogen atoms by mutual sharing of electrons. Therefore, the structural formula of methane consists of carbon atom bonded to four hydrogen atoms by single covalent bonds.