Question

Compare the radii of two species X and Y. Give reasons for your answer.

(a) X has 12 protons and 12 electrons (b) Y has 12 protons and 10 electrons

Answer 1

(a) For X

• Number of Protons= 12
• No of Electrons= 12
• So, atomic number= 12
• Electronic configuration- $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^2$
• So X should be Magnesium atom $\left(\mathrm{Mg}\right)$

(b) For Y

• Number of Protons= 12
• No of Electrons= 10
• So, atomic number= 12
• Electronic configuration- $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^0$
• So Y should be a Magnesium ion $\left({\mathrm{Mg}}^{2+}\right)$

Y has 10 electrons but X has 12 electrons so, the effect of nuclear charge on Y is greater than that of X, therefore the radius of Y is smaller as compared to X.