Select the larger member of each pair. (a) \(\mathrm{K}\) and \(\mathrm{K}^{+}\) (b) \(\mathrm{O}\) and \(\mathrm{O}^{2-}\) (c) \(\mathrm{Tl}\) and \(\mathrm{Tl}^{3+}\) (d) \(\mathrm{Cu}^{+}\) and \(\mathrm{Cu}^{2+}\)

To start, we need to identify the number of electrons and protons for each species. (a) K has 19 electrons and 19 protons, while K+ has 18 electrons and 19 protons. (b) O has 16 electrons and 8 protons, while O\(^{2-}\) has 18 electrons and 8 protons. (c) Tl has 81 electrons and 81 protons, while Tl\(^{3+}\) has 78 electrons and 81 protons. (d) Cu\(^{+}\) has 28 electrons and 29 protons, while Cu\(^{2+}\) has 27 electrons and 29 protons.

When an atom loses electrons, its size generally decreases. This is because there are fewer electrons to shield the electrostatic force from the protons in the nucleus, leading to a stronger attraction between the electrons and protons; thus, the electron cloud gets pulled in closer. Conversely, when an atom gains electrons, its size generally increases, as there are more electrons to shield the electrostatic force, leading to a weaker attraction between the nucleus and the electron cloud. (a) K is bigger than K+ because it has one more electron. The extra electron in K results in a weaker attraction with the nucleus, leading to a larger atomic size. (b) O\(^{2-}\) is bigger than O because it has two more electrons. The extra electrons in O\(^{2-}\) cause a weaker attraction with the nucleus, leading to a larger atomic size. (c) Tl is bigger than Tl\(^{3+}\) because it has three more electrons. The extra electrons in Tl result in a weaker attraction with the nucleus, leading to a larger atomic size. (d) Cu\(^{+}\) is bigger than Cu\(^{2+}\) because it has one more electron. The extra electron in Cu\(^{+}\) causes a weaker attraction with the nucleus, leading to a larger atomic size.

Taking into consideration the impact of the number of electrons on the size of the species, the larger member of each pair is: (a) K (b) O\(^{2-}\) (c) Tl (d) Cu\(^{+}\)