Question

The number of species below that has two lone pairs of electrons in their central atom is ______. (Round off to the Nearest Integer.)

${\mathrm{SF}}_4,{{\mathrm{BF}}_4}^{-},{\mathrm{CIF}}_3,{\mathrm{AsF}}_3,{\mathrm{PCl}}_5,{\mathrm{BrF}}_5,{\mathrm{XeF}}_4,{\mathrm{SF}}_6$

Answer 1

Structure of ${\mathrm{SF}}_4$:-

• In ${\mathrm{SF}}_4$, there are 4 Fluorine atoms that are attached to Sulphur.
• Electronic configuration of Sulphur with atomic number 16 is:$1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^4$.
• It shares its 4 electrons with Fluorine and thus form ${\mathrm{SF}}_4$that has a shape of Trigonal bipyramidal.

• From the structure we can see that it has 4 bond pairs$(\mathrm{S}-\mathrm{F})$and 1 lone pair.

Structure of ${{\mathrm{BF}}_4}^{-}$:-

• In ${{\mathrm{BF}}_4}^{-}$, there are 4 Fluorine atoms that are attached to Boron.
• Electronic configuration of Boron with atomic number 4 is:$1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^1$.
• It shares its 4 electrons with Fluorine and thus form ${\mathrm{SF}}_4$that has a shape of Tetrahedral.

• From the structure we can see that it has 4 bond pairs$(\mathrm{B}-\mathrm{F})$.
• The one extra electron that is left in Boron results in the negative charge of the compound.
• Thus we can also see that it has no lone pairs present in it.

Structure of ${\mathrm{ClF}}_3$:-

• In ${\mathrm{ClF}}_3$, there are 4 Fluorine atoms that are attached to Chlorine.
• Electronic configuration of Chlorine with atomic number 17 is:$1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^5$
• As we know, due to the presence of vacant d-orbital, Chlorine shows variable valency of $3,5,7$.
• It shares its 3 electrons with Fluorine and thus form ${\mathrm{ClF}}_3$that has a T-shape.
• 

• From the structure we can see that it has 3 bond pairs$(\mathrm{Cl}-\mathrm{F})$and 2 lone pair.

Structure of ${\mathrm{AsF}}_3$:-

• In ${\mathrm{AsF}}_3$, there are 3 Fluorine atoms that are attached to Arsenic.
• Electronic configuration of Arsenic with atomic number 33 is:$\left[\mathrm{Ar}\right]3{\mathrm{d}}^{10}4{\mathrm{s}}^{2}4{\mathrm{p}}^3$.
• It shares its 3 electrons with Fluorine and thus form ${\mathrm{AsF}}_3$that has a shape of Trigonal pyramidal.

• From the structure we can see that it has 3 bond pairs$(\mathrm{As}-\mathrm{F})$and 1 lone pair.

Structure of ${\mathrm{BrF}}_5$:-

• In ${\mathrm{BrF}}_5$, there are 4 Fluorine atoms that are attached to Bromine.
• Electronic configuration of Bromine with atomic number 35 is:$\left[\mathrm{Ar}\right]4{\mathrm{s}}^{2}3{\mathrm{d}}^{10}4{\mathrm{p}}^5$
• It shares its 5 electrons with Fluorine and thus form ${\mathrm{BrF}}_5$that has a square pyramidal shape.

• From the structure we can see that it has 5 bond pairs$(\mathrm{Br}-\mathrm{F})$and 1 lone pair.

Structure of ${\mathrm{PCl}}_5$:-

• In ${\mathrm{PCl}}_5$, there are 5 Chlorine atoms that are attached to Phosphorous.
• Electronic configuration of Phosphorous with atomic number 15 is:$1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^3$
• It shares its 5 electrons with Chorine and thus form ${\mathrm{PCl}}_5$that has a trigonal bipyramidal shape.

• From the structure we can see that it has 5 bond pairs$(\mathrm{P}-\mathrm{Cl})$and no lone pair.

Structure of ${\mathrm{XeF}}_4$:-

• In ${\mathrm{XeF}}_4$, there are 5 Fluorine atoms that are attached to Xenon.
• Electronic configuration of Xenon with atomic number 54 is:$\left[\mathrm{Kr}\right]4{\mathrm{d}}^{10}5{\mathrm{s}}^{2}5{\mathrm{p}}^6$
• It shares its 4 electrons with Fluorine and thus form ${\mathrm{XeF}}_4$that has a square planar shape.

• From the structure we can see that it has 5 bond pairs$(\mathrm{Xe}-\mathrm{F})$and has 2 lone pairs.

Structure of ${\mathrm{SF}}_6$:-

• In ${\mathrm{SF}}_6$, there are 6 Fluorine atoms that are attached to Sulphur.
• Electronic configuration of Sulphur with atomic number 16 is:$1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^4$
• It shares its 6 electrons with Fluorine and thus form ${\mathrm{SF}}_6$that has an Octahedral shape.

• From the structure we can see that it has 6 bond pairs$(\mathrm{S}-\mathrm{F})$and no lone pair.

Therefore, The number of species below that have two lone pairs of electrons in their central atom is 2 (${\mathrm{ClF}}_3,{\mathrm{XeF}}_4$).