Question

Which of the following options represents the correct ionic radii in Å of N^3-, O^2-, and F^- respectively?

• A. 1.71, 1.36 and 1.40
• B. 1.71, 1.40 and 1.36
• C. 1.36, 1.40 and 1.71
• D. 1.40, 1.36 and 1.71

Hint:

In anions, as the negative charge increases (more electrons added), the ionic radius increases due to greater electron-electron repulsion. Thus, \(\text{N}^{3-}\) has the largest ionic radius, followed by \(\text{O}^{2-}\), and \(\text{F}^-\) has the smallest.

Answer 1

The Correct Option is B

To understand the ionic radii of N^3-, O^2-, and F^-, let us consider the following points:

The ionic radius is the effective size of an ion in a crystal lattice.

The ionic radius depends on the charge of the ion: the more negative the charge, the larger the ionic radius, as additional electrons increase electron-electron repulsion.

For the same element in different ionic states, the more negatively charged ion will generally have a larger ionic radius because of the greater repulsion between the added electrons.

Now, let's examine each ion:

N^3- (Nitride ion) has the highest negative charge (3^-), which means it has gained three electrons. The added electrons cause the electron-electron repulsion to be high, which leads to an increase in size. This results in the largest ionic radius among the three ions. The ionic radius of N^3- is 1.71 Å.

O^2- (Oxide ion) has a charge of 2^-, meaning it has gained two electrons. It has less repulsion compared to N^3- but still exhibits a larger size than F^-. The ionic radius of O^2- is 1.40 Å.

F^- (Fluoride ion) has the smallest negative charge (1^-), which means it has only gained one electron. Since it has the least repulsion between electrons, it will have the smallest ionic radius among the three. The ionic radius of F^- is 1.36 Å.

Thus, the correct order of ionic radii is:

N^3- > O^2- > F^-

So, the correct answer is option (2) 1.71, 1.40, and 1.36.