Semimetals or metalloids possess characteristics of both metals and nonmetals. The members of this group are the least uniform in character. Semimetals may act as either metals or nonmetals, depending on the situation. In other words, in certain compounds, semimetals may bond with nonmetals (acting as metals), while in others they may bond with metals (acting as nonmetals).
The alkali metals are the elements found in group IA of the periodic table. All of these metals have one valence electron and are thus very reactive. They tend to have a softer consistency. The alkaline earth metals are the elements in group IIA of the periodic table. These elements have two valence electrons and have positive electron affinities.
The transition metals are the elements located in the B groups of the periodic table. Transition metals may have several oxidation states; that is, they give up their electrons fairly easily and have several to lose. Since the d orbitals are filling in this section of the periodic table, the d electrons are not in complete shells or subshells and may be removed. In addition, the outer two valence electrons (from a higher energy shell) may be removed. Since the electrons are so easily removed, the transition metals are extremely good conductors. These elements also have high melting and boiling points. They may form complexes with water when dissolved in solution.
