Carbon typically forms up to four covalent bonds because it has four valence electrons available for bonding, allowing it to share four pairs of electrons with other atoms to complete its octet and achieve stability

. The four bonds can be arranged in various ways, including:

• Four single bonds
• One double bond plus two single bonds
• Two double bonds
• One triple bond plus one single bond

This tetravalency is fundamental to carbon's chemistry and its ability to form complex molecules. However, there are rare exceptions where carbon can appear to exceed this four-bond limit. For example, in a special charged form of hexamethylbenzene, a carbon atom was experimentally shown to bond to six other carbon atoms. This unusual bonding involves weaker, longer bonds and electron sharing that is spread thin across more bonds than usual, so it does not violate the basic electron-sharing principle but represents an exceptional case

. In summary:

• Carbon normally forms up to four covalent bonds due to its four valence electrons

• It can form single, double, and triple bonds in various combinations to make up these four bonds

• Exceptional cases exist where carbon bonds to more than four atoms, but these are rare and involve unusual bonding situations