Arrange The Following Isoelectronic Series In Order Of Decreasing Radius:
F – , N3 – , O2 – ,Mg 2+, Na +.
Rank Ions From Largest To Smallest. To Rank Items As Equivalent, Overlap Them.
The correct answer and explanation is :
The ions provided—F⁻, N³⁻, O²⁻, Mg²⁺, and Na⁺—are isoelectronic, meaning they all have the same number of electrons. To arrange these ions in order of decreasing radius, we need to consider the following:
- Isoelectronic Ions: All the ions have the same electron configuration. Specifically, they all have 10 electrons, which corresponds to the electron configuration of neon (Ne): 1s² 2s² 2p⁶.
- Effective Nuclear Charge (Z_eff): The nuclear charge (Z) of each ion is different because they have different numbers of protons. The effective nuclear charge felt by the electrons increases with the number of protons, which causes a stronger attraction between the nucleus and the electron cloud, pulling the electrons closer to the nucleus and reducing the ion’s size.
- F⁻ has 9 protons, so its Z_eff is relatively low.
- N³⁻ has 7 protons, meaning it has the lowest Z_eff.
- O²⁻ has 8 protons, giving it a moderate Z_eff.
- Na⁺ has 11 protons, so its Z_eff is higher.
- Mg²⁺ has 12 protons, which gives it the highest Z_eff and pulls the electrons in the most tightly.
- Trends in Size: For isoelectronic ions, the ion with the fewest protons will experience the weakest pull on its electrons, resulting in the largest radius. Conversely, the ion with the most protons will experience the strongest pull on its electrons, resulting in the smallest radius.
Thus, the order of ions from largest to smallest radius is:
N³⁻ > F⁻ > O²⁻ > Na⁺ > Mg²⁺
Explanation:
- N³⁻ has the largest radius because it has the fewest protons, so the electrons experience the weakest pull from the nucleus.
- F⁻ follows because it has more protons than N³⁻ but fewer than O²⁻, leading to a slightly smaller radius.
- O²⁻ has more protons than F⁻ but fewer than Na⁺, so it is smaller than F⁻.
- Na⁺ is smaller than O²⁻ due to its higher nuclear charge.
- Mg²⁺ has the smallest radius because it has the most protons, resulting in the greatest pull on its electrons.
This trend is based on the balance between nuclear charge and electron-electron repulsion in isoelectronic species.