A carbon atom has 6 electrons, arranged in the configuration 1s2 2s2 2p2 1 s 2, 2 s 2, 2 p 2. The 2 electrons in the 1s orbital are not of interest in organic chemistry, as they do not partake in the reactions involved here. The remaining four electrons are the carbon atoms valence electrons, as these are available for forming covalent bonds. From the electron configuration, you would expect carbon to only form two bonds, but due to orbital hybridization, carbon can meet the octet rule of having eight electrons in its outer shell.