IB Chemistry HL 2.2.13 Expanded Octets Question Bank

Practise IB Chemistry HL 2.2.13 by drawing Lewis formulas for five- and six-domain species and using VSEPR to predict their electron and molecular geometries.

Exam points

identify period-three or heavier central atoms that can accommodate an expanded octet
draw Lewis structures with five or six electron domains and the correct lone pairs
deduce molecular shape from trigonal-bipyramidal or octahedral domain geometry

[Maximum number: 3]

Phosphoryl chloride, $\mathrm{POCl}_{3}$ , is a dehydrating agent.

(a)

$\mathrm{POCl}_{3}$ can be prepared by the reaction of phosphorus pentachloride, $\mathrm{PCl}_{5}$ , with tetraphosphorus decaoxide, $\mathrm{P}_{4} \mathrm{O}_{10}$ .

[ 3 ]

(i)

Deduce the Lewis (electron dot) structure of $\mathrm{PCl}_{5}$ .

[ 1 ]

Lewis structure of $\ce{PCl5}$ : phosphorus is the central atom with five single $\ce{P-}$ Cl bonds; phosphorus has an expanded octet and each chlorine has three lone pairs. Dots, crosses or lines for electron pairs are acceptable.

(ii)

Predict the shape of this molecule, using the valence shell electron pair repulsion theory (VSEPR).

[ 1 ]

$\ce{PCl5}$ has a trigonal bipyramidal shape.

(iii)

Identify all the different bond angles in $\mathrm{PCl}_{5}$ .

[ 1 ]

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2.2.13 (HL)—Expanded octets question 1

Question (a)

Question (i)

Question (ii)

Question (iii)