The seventh and last row again has fourteen inner transition metals, and the beginning of another series of transition metals. Only the first four of these transition metals have been prepared artificially, and none of them exists in nature.

The "eight-electron" elements - all of the elements except transition metals and inner transition metals - show the widest variety of chemical properties. They range from metals to nonmetals, and the boundary between these categories runs diagonally from upper left to lower right in the table. Because they illustrate the entire range of chemical properties, they are called the representative elements. The transition metals, although easily distinguishable from one another, are much more similar in behavior. All are metals, with a tendency to lose one to three electrons easily in chemical reactions. Iron (Fe), copper (Cu), tungsten (W), and gold (Au) are not difficult to distinguish, but neither are they as different, for example, as hydrogen, lithium, chlorine, and carbon. The inner transition, or rare earth, metals are so similar to one another that they can be separated only with great care. One rare earth, "didymium," discovered in 1885, later was found to be a mixture of two elements, which were christened neodymium (Nd) and praseodymium (Pm).