A carbon atom has four valence electrons. These are the electrons in carbon’s outer, second energy level and largely determine how the element bonds with other atoms.
Carbon’s atomic number is 6, giving a neutral atom the electron configuration 1s² 2s² 2p². The inner 1s² pair is not part of the valence shell; the remaining two 2s electrons and two 2p electrons make four valence electrons.
That arrangement helps explain carbon’s extraordinary chemistry. Rather than usually gaining or losing four electrons, carbon commonly shares electrons through covalent bonds. It can form four single bonds, as in methane, or combinations of single, double, and triple bonds. This tetravalence allows chains, rings, and large molecular structures.
A common mix-up is to answer 6, carbon’s total number of electrons, or 8, the stable-shell target described by the octet rule. Carbon starts with four outer electrons and can share four more in compounds, giving it an effective octet.