10. Playing with a Full Deck:
       The Periodic Table
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       The Transition Metals

Transition metals exhibit many different oxidation states, more than for any other class of elements. For reasons that we shall see in the next section, ions in many of these states are brightly colored, which indicates the electronic absorption of energy in the visible spectrum. The name "chromium" came from "chroma" for color. In principle, the maximum oxidation number for a transition metal would be the total number of outer s and d electrons, and this maximum indeed is found from scandium (Sc) to manganese (Mn), with 3 to 7 outer electrons (see above).


Each d electron can go into a separate orbital in these elements, so pairing of two electrons with opposite spin in the same orbital is not necessary. Pairing to fill an orbital must begin with iron (Fe), and this pairing effectively removes both electrons from bonding activity. The maximum oxidation number decreases in the progression from iron to zinc (Zn) at the end of the first transition-metal series. The +2 and +3 states are most common for these latter transition metals.

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