Hydrogen and chlorine were originally used as examples of univalent atoms, because of their nature to form only one single bond. Hydrogen has only one "valence electron" and can form only one bond with an atom that has an incomplete outer shell. Chlorine has seven "valence electrons" and can form only one bond with an atom that donates a "valence electron" to complete chlorine's outer shell. However, chlorine can also have oxidation states from +1 to +7 and can form more than one bond by donating "valence electrons".