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in the fourth and fifth rows except that they also have the lanthanides (first inner transition series) and actinides (second inner transition series). These come about by filling the 4f and 5f orbitals (see the many electron atom energy level diagram, Figure 11.1). The 4f (lanthanides) and 5f (actinides) orbitals (n = 4 and 5) are spatially much smaller than the 6s and 6p and 7s and 7p orbitals (n = 6 and 7) that are filled in the sixth and seventh rows because the principal quantum numbers, n, are smaller. The outermost electrons (largest principle quantum number) determine the chemical properties of atoms, that is, how many covalent bonds they make or what types of ions they form. Therefore, the 4f and 5f orbitals do not influence the chemical properties significantly. The lanthanides begin with lanthanum (La). The 4f energy levels are very close in energy to the 5d levels (see Figure 11.1). La comes after barium (Ba), which has two electrons in the 6s orbital. La has one more electron, which is actually in a 5d orbital. After La the 4f orbitals are filled. Lutetium (Lu, element 71) begins the third transition metal series. It has two electrons in the 6s orbital, 14 electrons in the 4f orbitals, and one electron in a 5d orbital. All of the lanthanides have chemical properties that are quite similar to La and Lu. In the same manner, the actinides begin with actinium (Ac). After filling the 5f orbitals with 14 electrons, lawrencium (Lr, the manmade element 103) begins the fifth transition metal series. All of the actinides have chemical properties that are very similar to Ac and Lr.

Most Elements Are Metals

The Periodic Table is color coded (shaded in Figure 11.4), with the elements divided into metals, semimetals (semiconductors), and nonmetals (insulators). (A detailed quantum theory explanation of why materials are metals, semiconductors, or insulators is presented in Chapter 19.) The Periodic Table shows that the vast majority of elements are metals. It is easy to see why this is. The left two columns are metals because they are comprised of elements that are either one or two s electrons past the previous noble gas closed shell configuration. They can readily give up these electrons to fall back to the closed shell configuration. Therefore, in solid form, it is easy to move electrons, and the solids are electrical conductors. Adding d electrons in the transitions series doesn’t eliminate the ability of an element to give up its outermost (highest n) s electrons. The d electrons only add more electrons that can be lost under the right circumstances. Adding f electrons doesn’t change things. Therefore, in addition to the two left-hand columns of elements, all of the transition series of elements are metals, usually called the transition metals. The inner transition series (addition of f electrons) are also metal. The elements that can lose three electrons to fall back to the previous closed shell configuration, like aluminum, are also metals. All of these together comprise most of the elements. The nonmetals are the group of elements in the upper right triangle-like block of elements in the Periodic Table. Some of these are the elements that tend to form covalent bonds by sharing electrons. They do not want to give up electrons. The halogens want to gain electrons or form covalent bonds. And the noble gases, by and large, do not want to gain or lose electrons or form covalent bonds. Therefore, all of these are nonmetals. If they are solids, the atoms do not want to give up electrons, a property necessary to conduct electricity. They are insulators. The small group of elements that form a diagonal block near the right side of the Periodic Table are semimetals or semiconductors. They are between the true metals and the nonmetals. Under some circumstances, they will conduct electricity. Silicon is the most well known and most technologically important of these semiconductors. Silicon is used in all of the microelectronics in our computers and other digital devices. In Chapter 19, we will discuss the differences