The far right group of the abbreviated periodic table is composed of the noble gases, helium, neon, and argon. Rather than losing electrons to produce positively charged cations, as is common with metals, the halogens readily gain electrons to complete their outer shell electron octets, producing F- and Cl- anions. These elements are the most nonmetallic of the elements. These elemental halogens are diatomic gases in which the two atoms of F2 or Cl2 are held together by a single covalent bond consisting of two shared electrons. The second group from the right, which in the abbreviated periodic table consists of fluorine and chlorine, is known as the halogens. These metals are highly reactive to form doubly charged cations (Be2+, Mg2+, Ca2+) by the loss of 2 electrons per atom. Freshly exposed surfaces of these metals have a grayish-white luster.
The second group of the abbreviated periodic table contains beryllium, magnesium, and calcium, all known as alkaline earth metals. The alkali metals react with elemental chlorine to produce the ionic chloride salts including, in addition to NaCl shown in Figure 3.8, LiCl and KCl. To produce the metal hydroxides, strongly basic substances that can be very destructive to flesh that they contact. The alkali metals (represented by M, below) react violently with water, Freshly cut, an alkali metal surface has a silvery-white color which almost instantaneously turns to a coating of gray metal oxide with exposure to air. In the elemental state alkali metals have a very low density and are so soft that they can be cut with a knife. Excluding hydrogen, the elements in the first group on the left of the table - lithium, sodium, and potassium - are alkali metals.
Otherwise, the elements in vertical columns belong to groups with similar chemical properties. In examining the periodic table, hydrogen should be regarded as having unique properties and not belonging to a specific group. Abbreviated 20-element version of the periodic table showing Lewis symbols of the elements.
As will be seen in later chapters, the chemistry of the first 20 elements tends to be straightforward and easily related to the atomic structures of these elements. This very simple, brief table contains much useful information, and it is recommended that the reader become familiar with it and be able to reproduce the Lewis symbols for each of the 20 elements. It is seen that the symbols of the elements in the same vertical columns have the same number of dots showing identical configurations for their outer-shell electrons. In addition to atomic number and atomic mass, this table shows the Lewis symbol of each element. The abbreviated periodic table with the first 20 elements is illustrated in Figure 3.9.
Among these elements are thorium, uranium, and plutonium, which are important in nuclear energy and nuclear weaponry. Also included are the lanthanides and the actinides. Among the heavier elements in the complete periodic table are the transition metals, including the important metals chromium, manganese, iron, cobalt, nickel, and copper. However, these elements are important and they are all shown in the complete periodic table at the end of this chapter. As noted above, the placement of electrons in elements with atomic number 21 and higher is a little too complicated to explain here. With element number 20, all of the elements required for the abbreviated periodic table have been described.