HardChemistryHigh School (11–12)The p-Block ElementsConceptualNumerical

Eight species are given: SF₄, XeF₄, ClF₃, XeO₃, IF₇, XeOF₄, ClO₄⁻ and I₃⁻…

Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

Eight species are given: $\text{SF}_{4}$ , $\text{XeF}_{4}$ , $\text{ClF}_{3}$ , $\text{XeO}_{3}$ , $\text{IF}_{7}$ , $\text{XeOF}_{4}$ , $\text{ClO}_{4}^{-}$ and $\text{I}_{3}^{-}$ . For each, find the lone pairs on the central atom and the shape. Then count three things. First, how many of the eight have at least one lone pair on the central atom? Second, how many have the hybridisation sp3d? Third, how many have a zero dipole moment, because their shape is symmetrical? Assume that every bond to the central atom is polar, except in $\text{I}_{3}^{-}$ , which is symmetrical by shape. Use $V = 6$ for sulphur, 8 for xenon, 7 for chlorine and iodine.

Need a reminder? The key ideaShow

For the central atom, lone pairs $= (V - \text{electrons taken by the ligands} - \text{charge})/2$ , and the steric number is the number of bonded atoms plus the lone pairs. In a trigonal bipyramid a lone pair prefers an equatorial place, where it has fewer neighbours at 90°. The order of repulsion is lone pair-lone pair, then lone pair-bond pair, then bond pair-bond pair.

The worked solution

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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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