Question

for each of the following pairs indicate which of the following two species is of the larger size
a) Fe2+ and Fe3+
b) Mg2+ and Ca 2+​

Answer 1

Answer:

B) Mg2+ and Ca2+ is of the larger size.

Answer 2

Answer:

For a: The size of $Fe^{2+}$ ion is large.

For b: The size of $Ca^{2+}$ ion is large.

Explanation:

For ions, the effective nuclear charge changes than the neutral atom.

There are two types of ions:

• Cations: They are formed when an atom looses its valence electrons. They are positive ions.
• Anions: They are formed when an atom gain electrons in its outermost shell. They are negative ions.

The size of the cation is small then their neutral atom. This is so because, the ion has less number of electrons while its nuclear charge remains the same. So, the nucleus attracts the electron more towards itself and leads to the decrease in size.

For a:  $Fe^{2+}\text{ and }Fe^{3+}$

As, the charge of the cation increases, the effective nuclear charge also increases, which results in the decrease of size of the cation.

Hence, the size of $Fe^{2+}$ ion is large.

For b:  $Mg^{2+}\text{ and }Ca^{2+}$

On moving down the group, the size of neutral atom increases because of the addition of new shell around the nucleus of an atom.

So, the size of ion will also increase as we move down the group.

Hence, the size of $Ca^{2+}$ ion is large.