Size correlates beautifully with electronegativity. The larger the atom, the weaker its hold on its outer-shell electrons, and the easier it is for another atom to take them away. Electronegativities of the representative elements are shown in color below. They range from 0.7 for cesium at the lower left, to 4.0 for fluorine at the upper right. We encountered cesium in Chapter 7, in connection with the photoelectric effect, as the electron-losing metal that is employed in electric eyes and photocells. It was mentioned previously that the omission of the transition metals between Groups IIA and IIIA was detectable by the sudden decrease in metallic radii, as shown in the table on the lower left page. They also are responsible for the unusual increase in electronegativity values (right), from 1.0 in Ca to 1.6 in Ga, and from 1.0 in Sr to 1.7 in In.

Lines connecting elements of equal electronegativity would extend diagonally from the upper left of the table to the lower right. Since electronegativity is chiefly responsible for determining chemical behavior, the chemical properties of the elements also show diagonal trends, as we have seen previously. The elements with amphoteric oxides cut a diagonal swath down the table, from Be to Al, Ge, and Sb. Weak, barely acidic oxyacids are formed by B, Si, As, and Te, whereas the common strong laboratory oxyacids are derived from N and S. This diagonality of properties also extends to the metal-nonmetal boundary and the solid-gas boundary for nonmetals, as the table at the beginning of the chapter indicates. The elements become more metallic downward in each group, and to the left across each row.