The carbon atom has four valence
electrons, whereas each of the four hydrogen atoms has a single valence electron.
Each hydrogen atom can acquire a helium electron configuration (two 1s valence
electrons) when the carbon atom shares with it one electron. The carbon now has
four additional shared electrons, one from each hydrogen, for a total of eight valence
electrons, and the electron structure of neon. The covalent bond is directional; that
is, it is between specific atoms and may exist only in the direction between one atom
and another that participates in the electron sharing.