Organic chemistry is a very vast and complex subject. There are millions of known organic compounds—far more than the number of inorganic compounds. The reason for this lies within the uniqueness of carbon's structure and bonding capabilities. Carbon has four valence electrons, and therefore makes four separate covalent bonds in compounds. Carbon has the ability to bond to itself repeatedly, making long chains of carbon atoms, as well as ringed structures. These bonds can be single, double, or triple covalent bonds. Carbon readily makes covalent bonds with other elements—primarily hydrogen, oxygen, nitrogen, halogens, and several other nonmetals.