Question

Which has the smallest size?
(a) $N{{a}^{+}}$
(b) $A{{l}^{+3}}$
(c) $M{{g}^{+2}}$
(d) ${{P}^{+5}}$

Answer 1

Hint: As we move from left to right, atomic radii decreases and hence, size also decreases and as we move from top to bottom, the atomic radii increases and hence, size also increases, and always remember that the size of the cation is always smaller than the anion. Now, Identify the smallest cation from the above given cations.

Complete step by step answer:
-First of all, let's discuss what an atomic radius is. By the term atomic radius, we mean the average distance of the outermost shell from the nucleus.
-The atomic radii and the size decreases as we move from right to left of the periodic table and increases as we move from top to bottom of the periodic table.
-Moreover, the cations have smaller atomic radii than the anions. It is so because after losing the electrons , the number of protons in the nucleus increases resulting in the increase of the nuclear charge and hence, the electrons present in the element are more strongly attracted by the nucleus and hence, its atomic radius decreases and thus , the size also decreases.
-Greater the charge on the cation, smaller is the size of the cation and vice-versa. So, from the above given all cations, we can see that phosphorus has the greatest charge on it i.e. +5 and its electrons are very strongly attracted by the nucleus due to the increased nuclear and thus, has the smallest size.

Hence, option (d) is correct.

Note: Atomic radii is divided into three types;
1. Covalent radius : the distance between the two atoms when they are bound by a single bond in a covalent molecule is called the covalent radius.
2. Van Der Waals radius: the one half the distance between the nuclei of the two non covalently bonded atoms is called the Van Der Waals radius.
3. Metallic radius: it is one half the internuclear distance between the two adjacent metal atoms.