Structure and Bonding — A/L Chemistry

How do I practise Structure and Bonding?

1 question with a worked solution

Check before you answer: VSEPR Theory & Molecular Geometry: Deducing electron pair geometry and actual molecular shape by accounting for lone pair-lone pair > lone pair-bond pair > bond pair-bond pair repulsion hierarchies.

1. According to VSEPR theory, what is the molecular shape and the approximate bond angles of sulfur tetrafluoride (SF₄)?
   1. A) Tetrahedral shape with bond angles of 109.5°
   2. B) Square planar shape with bond angles of 90°
   3. C) See-saw shape with bond angles < 120° and < 90°
   4. D) Trigonal bipyramidal shape with bond angles of 120° and 90°
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   Correct answer: C) See-saw shape with bond angles < 120° and < 90°

   Sulfur has 6 valence electrons; in SF₄ it forms 4 single bonds with fluorine and retains 1 lone pair (total 5 electron pairs). The electron pair geometry is trigonal bipyramidal. The lone pair occupies an equatorial position to minimize repulsion, resulting in a see-saw molecular shape with bond angles slightly compressed to <120° and <90°.

   Show worked solution

   Step 1: Total valence electrons for S = 6. 4 F atoms share 4 electrons to form 4 bond pairs. Step 2: Remaining electrons on S = 6 - 4 = 2 electrons = 1 lone pair (AX₄E notation). Step 3: Total steric number = 4 + 1 = 5. Basic arrangement is trigonal bipyramidal. Step 4: Applying lone pair - bond pair repulsion hierarchies, the lone pair occupies an equatorial site, bending axial F-S-F bonds to ~173° (<180°) and equatorial F-S-F bonds to ~102° (<120°). Answer: See-saw shape with bond angles < 120° and < 90°.
   Modelled on: the A/L Chemistry examination pattern

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Where does Structure and Bonding fit in the syllabus?

Grade 12 · Term 1