Question

The first ionisation potentials of four consecutive elements present in the second period of periodic table are $8.3,11.3,14.5$ and $13.6$ eV respectively which one of the following is the first ionisation potential of nitrogen?

• A. $13.6$
• B. $14.5$
• C. $11.3$
• D. $8.3$

Answer 1

The correct option is B $14.5$

Elements of $2^{nd}$ period: ${}_{3}Li{}_{4}Be{}_{5}B{}_{6}C{}_{7}N{}_{8}O{}_{9}F{}_{10}Ne$

${}_{7}N\Rightarrow 1s^{2}2s^{2}2p^3$

$N$ is more electronegative among the elements. Also has a stable half-filled electron configuration due to which it will have a high first $IP$ but less than $Ne$ as $Ne$ is an inert gas. But the $IP$ value of $Ne$ is more than $14.5eV$ due to its' inertness.

$\therefore$ $IP$ of $N$ is $14.5eV$.