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7 Periodic Properties of the Elements Solutions to Exercises (b) Si K>Li (b) Pb > Sn > Si (c) N>O>F 7.26 (a) Na Mg²⁺ > Be²⁺ (c) Fe: [Ar]4s²3d⁶; [Ar]3d⁵. The 4s valence electrons in Fe are on average farther from the nucleus than the 3d electrons, so Fe is larger than Since there are five 3d orbitals, in at least one orbital must contain a pair of electrons. Removing one electron to form Fe³⁺ significantly reduces repulsion, increasing the nuclear charge experienced by each of the other d electrons and decreasing the size of the ion. Fe > > Fe³⁺ 7.29 The size of the red sphere decreases on reaction, so it loses one or more electrons and becomes a cation. Metals lose electrons when reacting with nonmetals, so the red sphere represents a metal. The size of the blue sphere increases on reaction, so it gains one or more electrons and becomes an anion. Nonmetals gain electrons when reacting with metals, so the blue sphere represents a nonmetal. 7.30 The order of radii is > Br > F, so the largest brown sphere is Br, the intermediate blue one is Br, and the smallest red one is F. 171