Question

Which electronic configuration of an element has abnormally high difference between second and third ionisation energy?

• A. $1s^2,2s^2,2p^6,3s^1$
• B. $1s^2,2s^2,2p^6,3s^2,3p^1$
• C. $1s^2,2s^2,2p^6$
• D. $1s^2,2s^2,2p^6,3s^2$

Answer 1

The correct option is D $1s^2,2s^2,2p^6,3s^2$

(a) $1s^{2}2s^{2}2p^{6}3s^1\stackrel{+E_1}{\to }1s^{2}2s^{2}2p^6$ $\stackrel{+1E_2}{\to }1s^{2}2s^{2}2p^5\stackrel{+1E_3}{\to }1s^{2}2s^{2}2p^4$

(b) $1s^{2}2s^{2}2p^{6}3s^{2}3p^1\stackrel{+E_1}{\to }1s^{2}2s^{2}2p^{6}3s^2$$\stackrel{+1E_2}{\to }1s^{2}2s^{2}2p^{6}3s^1\stackrel{+1E_3}{\to }1s^{2}2s^{2}2p^6$

(c) $1s^{2}2s^{2}2p^6\stackrel{+E_1}{\to }1s^{2}2s^{2}2p^5\stackrel{+1E_2}{\to }1s^{2}2s^{2}2p^4$ $\stackrel{1E_3}{\to }1s^{2}2s^{2}2p^3$

(d) $1s^{2}2s^{2}2p^{6}3s^2\stackrel{+E_1}{\to }1s^{2}2s^{2}2p^{6}3s^1$$\stackrel{+1E_2}{\to }1s^{2}2s^{2}2p^6\stackrel{+1E_3}{\to }1s^{2}2s^{2}2p^5$

In option D, after removal of second valence electron from 3s orbital, the ion formed achieves noble gas configuration. Therefore, to remove the third electron from 2p orbital, a lot of energy is required. Thus, there is an abnormally high difference between second and third ionization enthalpies.