Question

The increasing order of the first ionisation enthalpies of the elements $B,P,S$ and $F$ is:

• A. $B<S<P<F$
• B. $F<S<P<B$
• C. $P<S<B<F$
• D. $B<P<S<F$

Answer 1

Answer: (A)

$B<S<P<F$

In general:
(i) First ionization energy $(I.E_1)$ or enthalpy, increases along the period from left to right, but due to half-filled configuration of $P-atoms$, it has higher $I.E_1$ than of $S-atom$.
(ii) $I{E}_1$ decreases as we move down the group from top to bottom.
(iii) More is the size of an atom, less is the $I{E}_1$.
Hence, correct order of $I{E}_1$ is $B<S<P<F$.
$I{E}_1$ for (in $kJmo{l}^{-1})$
$B=800$
$S=999.4$
$P=1012$
$F=1680.8$.