Question

Which of the following series of isoelectronic ions (Mg²⁺, N³⁻, F⁻, Si⁴⁺) has the ionic radii in order of largest to smallest? A) Mg²⁺ > N³⁻ > F⁻ > Si⁴⁺ B) Mg²⁺ > Si⁴⁺ > F⁻ > N³⁻ C) N³⁻ > F⁻ > Si⁴⁺ > Mg²⁺ D) N³⁻ > F⁻ > Mg²⁺ > Si⁴⁺ E) F⁻ > N³⁻ > Si⁴⁺ > Mg²⁺

Answer 1

Answer:

Option (d) is correct

N³⁻ > F⁻ > Mg²⁺ > Si⁴⁺

Explanation:

Total electrons for all the species = 10

So these are iso electronic with each other.

We know

Ionic radii ∝ $\frac{Magnitude of Negative Charge}{Magnitude of Positive Charge}$

• Si⁴⁺ has 14 protons and 10 electrons
• Mg²⁺ has 12 protons and 10 electrons
• N³⁻ has 7 protons and 10 electrons
• F⁻ has 9 protons and 10 electrons

• Iso electronic species with greatest number of protons have small size and vice versa.
• So Si⁺⁴ have smallest size and N³⁻ have largest in size