Chapter 7

Q. 7.PS.12

Trends in Ionic Sizes

For each of these pairs, choose the smaller atom or ion:
(a) A Cu atom or a Cu^{2+} ion
(b) A Se atom or a Se^{2-} ion
(c) A Cu^+ ion or a Cu^{2+} ion


Verified Solution

(a) Cu^{2+} ion           (b) Se atom           (c) Cu^{2+} ion

Strategy and Explanation Consider the differences in the sizes of atoms and their corresponding ions based on electron loss or gain.
(a) A cation is smaller than its parent atom; therefore, Cu^{2+} is smaller than a Cu atom.
(b) Anions are larger than their parent atoms, so a Se^{2-} ion is larger than a selenium atom.
(c) Both copper ions contain 26 protons, but Cu^{2+} has one fewer electron than does Cu^+.
Correspondingly, the radius of Cu^{2+} is smaller than that of Cu^+.