Test Index

p Block Elements

Section: Chemistry

Question : 25 of 60

Marks: +1, -0

\mathrm{X}_2

decrease in ionization energy down the group
decrease in HOMO-LUMO gap down the group
decreases in $\pi^{*}-\sigma^{*}$ gap down the group
the physical state of $\mathrm{X}_2$ at room temperature changes from gas to solid down the group.

Solution:

Electronic configuration of

\mathrm{F}_2

molecule is

\sigma^{2}_{1s},\sigma^{*2}_{1s},\sigma^{2}_{2s},\sigma^{*2}_{2s},\sigma^{2}_{2p_z},\pi^{2}_{2p_x}\pi^{2}_{2p_y},\pi^{*2}_{2px},\pi^{*2}_{2p_y},\sigma^{*2}_{2p_z}

⇒ Similar electronic configuration for other

\mathrm{X}_2

molecules.

⇒

\pi^{*}_{p_x}

and

\pi^{*}_{p_y}

are highest energy occupied molecular orbital (HUMO) and

\sigma^{*}_{p_z}

is lowest energyunoccupied molecular orbital (LUMO).

⇒ Colour of

\mathrm{X}_2

molecules of group 17 elements is due to transition of electrons from

\pi^{*}

and

\sigma^{*}

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