Maharashtra State PSC Model Paper 5

The correct answer is Two or more species with the same number of atoms, the same number of valence electrons, and the same structure, regardless of the nature of elements involved.

• Two or more species with the same number of atoms, the same number of valence electrons, and the same structure, regardless of the nature of elements involved are known as isoelectronic species.
• ${\mathrm{N}}^{3-},{\mathrm{O}}^{2-},{\mathrm{F}}^{-},\mathrm{Ne},{\mathrm{Na}}^{+},{\mathrm{Mg}}^{2+},$ and ${\mathrm{Al}}^{3+}$ are some of the examples of isoelectronic species.
• Their atomic radii would be different because of their different nuclear charges.
• The cation with the greater positive charge will have a smaller radius because of the greater attraction of the electrons to the nucleus.
• The anion with the greater negative charge will have a larger radius because the net repulsion of the electrons will outweigh the nuclear charge and the ion will expand in size.