Question

Which ion has the largest radius? $ N{a^ + },G{a^{3 + }},{K^ + },M{g^{2 + }},C{a^{2 + }} $ .

Answer 1

Hint: The atomic radius is generally defined as the total distance from an atom’s nucleus to the outermost orbital of electrons. It is similar to the radius of the circle. As we move down the group or across the period the atomic radius changes. The radius we need to find is an ionic radius.

Complete Step By Step Answer:
The ionic radius is the radius of an atom forming an ionic bond or an ion. The radius of each atom in an ionic bond will be different from that of the covalent bond. In the question the element is cation, containing positive charge so, the size is smaller.
In the periodic table, atomic radii decrease from left to right across a row and increase from top to bottom down the group. This trend is because of the difference in the effective nuclear charge experienced by the electrons in the outermost orbitals of the element. The greater the effective nuclear charge, the more strongly the outermost electrons are attracted to the nucleus and the smaller the atomic radius.
 For the cation, which is an ion with a positive charge, by definition has fewer electrons than protons. The loss of electrons means that there are now more protons than electrons. The effective nuclear charge felt by the remaining electrons increases because there are fewer electrons to shield one another from the nucleus.
Thus, potassium has the largest radius and the magnesium has the smallest radius, the order will be:
  $ {K^ + } > N{a^ + } > C{a^{2 + }} > G{a^{3 + }} > M{g^{2 + }} $ .

Note:
Cation having lots of electrons, is always smaller than its parent neutral atom and an anion, having gained an electron, is always larger than the parent neutral atom. The ionic radius follows the same trend as atomic radius, the ionic radius increases going down a column and decreases from left to right.