Final answer:
Silver is less reactive than rubidium because after losing its outermost electron, silver achieves a stable filled d-subshell, while rubidium has a less stable closed shell. Silver has a smaller atomic radius, which means its valence electron is held more tightly by the nucleus compared to the larger rubidium atom, whose valence electron is more easily removed.
Step-by-step explanation:
The question asks why silver is far less reactive than rubidium, even though both form +1 ions. This can be explained by considering their ground-state electron configurations and atomic radii. Silver's electron configuration is [Kr]4d105s1 and it forms a stable 4d10 configuration upon losing its outermost electron, which gives silver a filled d-subshell contributing to its low reactivity. In contrast, rubidium has the electron configuration [Kr]5s1 and when it loses its lone valence electron, it results in a [Kr] core, which is less stable compared to a filled d-subshell. Additionally, the large atomic radius of rubidium makes the outer electron easier to remove, as it is farther from the nucleus and feels less nuclear charge.
Regarding ionic radii, cations are smaller than their neutral atoms because the loss of an electron leads to a decrease in electron-electron repulsion and allows the remaining electrons to be pulled closer to the nucleus. For instance, the Na+ ion is smaller than the Na atom because it has one less electron, resulting in a closed shell with n = 2. On the other hand, anions are larger than their neutral atoms due to the addition of electrons causing increased electron-electron repulsion, and the increased electron cloud size without an increase in nuclear charge, as in the case of the Na- ion.