Question

What is the correct order of size in each pair given below? $Ni$ and $N{i^{2 + }}$
(A) $Ni = N{i^{2 + }}$
(B) $Ni < N{i^{2 + }}$
(C) $Ni > N{i^{2 + }}$
(D) None of these

Answer 1

When electrons are removed from an atom, it results in the ion of that atom. If electrons are added to an atom, the resulting ion will be larger than the parent atom. Atomic radii increases as we go from the top to bottom of the periodic table and decreases as we go from left to right in the periodic table.

Complete answer:
The atomic radius of $Ni$ atom is greater than the ionic radius of $N{i^{2 + }}$ ion. When two electrons are removed from the $Ni$ atom, $N{i^{2 + }}$ ion is formed. The ratio of the number of protons to the number of electrons is higher for the ion $N{i^{2 + }}$ . As there is a higher effective nuclear charge in $N{i^{2 + }}$ , the nucleus will pull the electrons towards itself to a greater extent than that in $Ni$ atom. This will result in a smaller ionic radius for $N{i^{2 + }}$ .
Therefore, option C is the correct answer.

Note:
Ionic radius is half of the distance between the atomic ions in a given crystal lattice. The ionic radius increases as we move down in a periodic table. If the effective nuclear charge on the valence shell decreases, the ionic radius will increase. Any atom or a group of atoms which bear one or more than one positive or negative electrical charges are called ions. The ions which are positively charged are called cations whereas the ions which are negatively charged are called anions.