Atomic Radii and Periodic Trends
Using only a periodic table, list these atoms in order of decreasing size: Br, Cl, Ge, K, S.
K > Ge > Br > S > Cl
Strategy and Explanation Based on the periodic trends in atomic size, we expect the radius of Cl to be smaller than that of Br, which is below it in Group 7A; S in Period 3 should be smaller than Br, which is in Period 4. Because size decreases across a period, we expect Cl to be smaller than S. Of the Period 4 atoms, Ge is earlier in the period than Br and therefore larger than it, but smaller than K, which starts the period. From these trends we can summarize the relative sizes of the radii, from largest to smallest, as K > Ge > Br > S > Cl.