PERIODIC TABLE

Chemists of the nineteenth century noticed that many elements have similar chemical properties. Numerous attempts were made to arrange the elements into some systematic fashion to emphasize these similarities. The most successful arrangement was arrived at independently by two chemists, Dmitri Mendeleev and Lothar Meyer. They grouped the elements with similar properties together into families and designed the first periodic table of the elements. The modern periodic table is a direct descendant of the original Meyer-Mendeleev arrangement of the elements.
The periodic table consists of a number of columns called groups. The horizontal rows are called periods. The elements in each gcouo have similar chemical and physical properties. For example, the elements at the far right of the periodic table, called the noble gases, are the least reactive of all the elements. The elements in group IA are called the alkali metals. Those in group IIA are called the alkaline earth metals. The transition metals are the elements located in groups IIIB to IIB. The halogens are the elements in group VIIA. All the members of a group have similar physical and chemical properties.
The elements are divided into three classes based on their physical properties. Elements that show a metallic luster when polished, are capable of being drawn out into wire, can be hammered into sheets, and are good conductors of heat and electricity ars classed as metals. Elements that do not have these properties are classed as nonmetals. A class between these two is called the metalloids, or borderline elements. Elements of the three classes are shown in the periodic table in Figure 1. There is a zigzag line on the right side of the periodic table that separates the nonmetals on the right from the metals on the left. Near this line are the metalloids. These elements such as silicon (Si) and germanium (Ge), have some properties that are similar to those of nonmetals and some that are similar to those of metals.