Metal

The first element of the periodic table, hydrogen, is a nonmetal. In the case of the alkali metals of Group 1, however, one finds that lithium, sodium, potassium, rubidium, cesium, and francium all exhibit to a high degree typically metallic properties. Each of these atoms has one electron in the outermost energy level. The energies required to pull off these single valence electrons are relatively small; on the other hand, the energies required to pull off a second electron are many times higher.

Group 2 of the periodic table includes the elements beryllium, magnesium, calcium, strontium, and radium. These elements are known as the alkaline earth metals. In each of the Group 2 elements, there are two electrons in the outer-most energy level. Going down the group from beryllium to radium, one finds decreasing ionization potentials with increasing ionic radius. In general, the larger atoms hold their electrons less tightly than do the smaller atoms. Although the first two electrons are removed relatively easy, removal of a third electron from the Group 2 elements requires very high energies.

Groups 3 through 12 in the periodic table are known as the transition elements. The most characteristic property of the transition elements is that they are all metals. This is because the outermost electron shells of these elements contain very few electrons. Unlike the Group 1 and 2 elements, the transition metals tend to be hard, brittle, and fairly high melting. The difference is due in part to the relatively small size of the transition element radii, and partly to the existence of some covalent bonding between the ions.

The Group 13 elements have the same relationship to the alkaline earth elements that the alkaline earth elements have to the alkali metals, that is, the group properties are modified by the presence of a third valence electron. The elements of Group 13 are boron, aluminum, gallium, indium, and thallium. Except for boron, which may be classified as a semimetal, these elements tend to show metallic properties.

Group 14 elements include carbon, silicon, germanium, tin, and lead. As already noted, carbon forms a solid of complex structure that does not exhibit metallic properties. The second and third members of the group, silicon and germanium, cannot be classified as metals either; they are only semimetals.

In Group 15, there is a complete change of properties from nonmetallic to metallic in going down the group. The lighter members, nitrogen and phosphorous, are typically nonmetals. The middle members, arsenic and antimony, are semimetals. The heaviest member, bismuth, is a metal.

The Group 16 elements include oxygen, sulfur, selenium, tellurium, and polonium. As would be expected from their location on the far right of the periodic table, the Group 16 elements have high ionization potentials, and metallic properties are difficult to observe. However, in going down the group, electrons are less tightly held; so there is some suggestion of metallic behavior in the heavier Group 16 elements.

The Group 17 elements, i.e., fluorine, chlorine, bromine, iodine, and astatine, all have high electronegativities and consequently show practically no metallic properties. Iodine, however, does show some metallic characteristics. Astatine may have some metallic properties, but it is a short-lived radioactive element, and measurements of its properties are difficult to carry out.

The Group 18 elements, or noble gases, consist of six gases: helium, neon, argon, krypton, xenon, and radon. The noble gases are nonmetals.