Question

For each of the following pair indicate which of the ion is larger in size
1)Fe2+,Fe3+
2)Mg2+,Ca2+

Answer 1

Answer:

Fe2+ is greater in size than Fe3+.

Explanation:

Consider the electronic configuration of Fe2+[Ar] 3d6 and Fe3+[Ar] 3d5 (For comparison, Fe [Ar] 4s2 3d6). Fe3+ ionic radius is 63 pm, while Fe2+ has an ionic radius of 77 pm. (For comparison, the Fe atom has a radius of 140 pm). This is because the outermost electron in the Fe2+ ion is pulled off to form Fe3+ ion. As the electrons are removed, it reduces the repulsion increasing nuclear charge experienced by each of the other d electrons and decreases the size of the ion.