Question

Which of the following atoms would have the largest ionic radii?

• A. $F^{-}$
• B. $O^{-2}$
• C. ${Na}^{+}$
• D. ${Mg}^{+2}$
• E. ${Al}^{+3}$

Answer 1

Answer: (B)

$O^{-2}$

Option B is the correct answer.

In general anions have a larger radius than their corresponding atoms. $O^{-2}$ is an anion having two extra electrons than the corresponding atom $O$. Thus it has the largest radius.

We can also say, that as the number of electrons increases in the outermost shell, the nuclear force of attraction or pull of the nucleus on these electrons also decreases, and hence, the radius is increased.