Click down on the above molecule to display a menu of ways to manipulate it. Carbon is, along with hydrogen, oxygen and nitrogen, one of the most abundant atoms in living organisms. All of these atoms readily form covalent bonds by electron pair sharing. Hydrogen needs one electron, oxygen two, nitrogen three, and carbon four to complete their outer electron shells and thus form stable covalent bonds. These elements thus react with each other to form a large number of different covalent compunds.
Carbon atoms possess another, and most significant property, the capacity to bond with each other.
Since a carbon atom may either accept or donate four electrons, it can form covalent bonds with four other carbon atoms. Organic compounds of carbon have another distinctive feature. No other chemical element can form molecules of such widely different sizes and shapes or with such a variety of functional groups.