Why do some elements, like iron, have more than one valance number?
Some elements, like the transition metals, have electron configurations in which electrons from their inner shells can also be used as valence electrons; these elements can have several different oxidation states. For example, iron can have a valence of +2 or +3, and chromium can have a valence of +2, +3, or +6. Iron in the +3 oxidation state, Fe+3, acts as an oxidizing agent, accepting one electron to attain the Fe+2 state, while ferrous iron, Fe+2, by donating an electron in going to the +3 state, acts as a reducing agent.
