The correct decreasing order of first ionisat | vedclass

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Question

(C) The general trend for first ionization enthalpy across a period is that it increases from left to right due to an increase in effective nuclear ch

Vedclass · Accepted Answer

$F > N > C > O > Be > B$

Vedclass · Answer

(C) The general trend for first ionization enthalpy across a period is that it increases from left to right due to an increase in effective nuclear charge and a decrease in atomic size. However,there are exceptions due to stable electronic configurations. The electronic configurations of the second-period elements are: $Li (1s^2 2s^1)$,$Be (1s^2 2s^2)$,$B (1s^2 2s^2 2p^1)$,$C (1s^2 2s^2 2p^2)$,$N (1s^2 2s^2 2p^3)$,$O (1s^2 2s^2 2p^4)$,$F (1s^2 2s^2 2p^5)$,$Ne (1s^2 2s^2 2p^6)$. $Be$ has a fully filled $2s$ orbital,which is more stable than the $2p^1$ configuration of $B$. $N$ has a half-filled $2p$ orbital,which is more stable than the $2p^4$ configuration of $O$. Thus,the correct decreasing order for the elements $Be, B, C, N, F$ is $F > N > C > Be > B$.

The correct decreasing order of first ionisation enthalpies of five elements of the second period is

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