A carbon atom possesses four electrons in its outermost orbit. To reach stability, it therefore tends to form four covalent bonds. By sharing these four electrons, it acquires an additional four electrons from other atoms, completing its outermost shell with a total of eight electrons. Atoms that readily share electrons with carbon, thus forming bonds, include hydrogen, oxygen, nitrogen, halogens, and, naturally, other carbon atoms. These bonds are referred to as carbon-carbon bonds, carbon-hydrogen bonds, carbon-oxygen bonds, etc. (Note they are all covalent bonds.)