Because carbon has four valence electrons, it can form a maximum of four single covalent bonds in order to reach a full octet. Carbon can also form two double bonds or one triple bond. Note that double bonds are stronger than single bonds and triple bonds are stronger than double bonds.

Carbon is special because it can form long carbon-to-carbon chains. Carbon’s size and its four valence electrons allow it to make a large number of bonds compared to many other elements. This is why carbon is often a part of large molecules.