Question

(a) Explain the variation of ionisation energy along the group and period.
(b) Write any five uses of fluorine.

Answer 1

(a) Ionisation energy of an element is defined as the amount of energy required to remove the most loosely bound electron from isolated neutral gaseous atom in its lowest energy state.
$M_{\left(g\right)}+Energy\stackrel{I_1}{\to }{M}_{\left(g\right)}^{+}+e^{-}$
Periodic variation of ionisation energy
(a) Across the period: The value of ionisation energy increases from left to right with breaks where the atoms can attain a stable configuration by losing an electron. As we move across the period, effective nuclear charge increases, as the size decreases and it is difficult to remove the electrons from the valence shell. So, ionisation energy increases.
(b) Down the group: The value of ionisation energy decreases from top to bottom. Because as we move down the group, atomic size increases, the nuclear attraction decreases and it is easy to remove the electrons from valence shell. So, ionisation energy decreases.
(b) (i) Fluorine is used in the manufacture of Freon $\left(C{F}_{2}C{l}_2\right)$ which is used as refrigerants.
(ii) $Ca{F}_2$ is used as flux in metallurgy.
(iii) $NaF$ is used as preservative to prevent fermentation and also to prevent dental cavities.
(iv) $S{F}_6$ is used as an insulator.
(v) Teflon is used as a container for $HF$.
(vi) $U{F}_6$ is used in the separation of $U^{235}$ from $U^{238}$.