The transition metals are those elements found in the “d” block of the periodic table. If you aren’t familiar with that terminology, looking at the periodic table, the “d” block is the section beginning with the third column from the left and reaching all the way to the twelfth column. (This assumes that you have the standard representation of the periodic table that places the two rows of the “f” block – also called the lanthanides and actinides – underneath the rest of the table.)
The transition metals include most of your everyday metals – iron, copper, gold, silver, nickel, platinum, titanium (but not aluminum). You’ll also find a number of elements that you probably aren’t familiar with, like vanadium and ruthenium.
If you are familiar with electron configurations, the transition metals are the first elements encountered that revert to filling an inner shell instead of the outermost shell. This is because after the outermost “s” orbital has been filled, the “d” orbitals of the previous energy level provide a lower energy state than does the outermost “P” orbitals.
The important result of this different electron arrangement is that there are now multiple ways to achieve a stable ion. The “octet rule” is no longer truly a rule once the transition metals are reached. Instead, combinations that result in a half full (5) or completely full (10) “d”, an empty “d” but a full “s”, and the standard octet are all observed, as well as other patterns as well. With multiple stable patterns possible, many of the transition metals can produce ions of differing charges. Iron, for example, commonly will have either a +2 or +3 charge. (Charges from +5 to +1 can be made in the lab, but those are under more extreme circumstances.) Vanadium will have charges of +3, +4 or +5. Copper will normally be +1 or +2. Some of the transition metals are still only found with one common ionic form however. Silver is most always +1, zinc +2, and gold +3.
Because the charges of the ions of transition metals can vary, naming ionic compounds which include transition metals requires that the charge of the ion be stated. This is done by placing the charge of the ion in parenthesis using Roman numerals after the name of the transition metal. As a result, rust – Fe2O3, in which iron has a charge of +3, is properly named iron (III) oxide. This distinguishes it from FeO, which would be iron (II) oxide.