Question 1(a) in every paper from 2021 to 2025 was a table asking for two Lewis structures and the name of each shape. It is the most predictable set of marks in the standard. Draw the Lewis structure first, count the regions, then read the shape off the table. Lone pairs occupy space and push the bonds closer together, which is why the electron geometry and the molecular shape can differ.
Regions of electron density → shape (this table answers Q1a every year)
Regions
Bonding / lone
Electron geometry
Molecular shape
Bond angle
2
2 / 0
Linear
Linear
180°
3
3 / 0
Trigonal planar
Trigonal planar
120°
3
2 / 1
Trigonal planar
Bent
<120°
4
4 / 0
Tetrahedral
Tetrahedral
109.5°
4
3 / 1
Tetrahedral
Trigonal pyramidal
<109.5°
4
2 / 2
Tetrahedral
Bent
<109.5°
5
5 / 0
Trigonal bipyramidal
Trigonal bipyramidal
90° and 120°
5
4 / 1
Trigonal bipyramidal
Seesaw
<90°, <120°
5
3 / 2
Trigonal bipyramidal
T-shaped
<90°
5
2 / 3
Trigonal bipyramidal
Linear
180°
6
6 / 0
Octahedral
Octahedral
90°
6
5 / 1
Octahedral
Square pyramidal
<90°
6
4 / 2
Octahedral
Square planar
90°
ℹ
The ones they actually asked
SeF₄ and ClF₄⁻ (2021) · BrCl₅ and BrF₃ (2022) · SF₄ and SF₆ (2023) · PF₅ and SeCl₄²⁻ (2024) · SF₃⁻ and SBrF₅ (2025). Notice how many are five- and six-region species: seesaw, T-shaped and square planar come up far more than the simple tetrahedral cases, so practise those. Worked example SF₄ (asked in 2023 and 2025) Give the Lewis structure and name the shape of sulfur tetrafluoride, SF₄. Valence electrons: S has 6, each F has 7. Total = 6 + (4 × 7) = 34. Four S–F bonds use 8 electrons; 24 more complete the fluorine octets. That leaves 2. The remaining pair sits on the sulfur, so S has 4 bonds + 1 lone pair = 5 regions. Five regions → trigonal bipyramidal electron geometry. The lone pair takes an equatorial position. ✓ Shape = seesaw. Bond angles slightly less than 90° and 120°, because the lone pair repels more strongly than a bonding pair. Worked example Bond angles: SF₄ vs SBrF₅ (2025, Excellence) Justify why the F–S–F bond angles in SF₄ differ from those in SBrF₅. SF₄: 4 bonds + 1 lone pair = five regions of electron density → trigonal bipyramidal geometry → angles of 90° and 120°. SBrF₅: 6 bonds + 0 lone pairs = six regions → octahedral geometry → all angles 90°. More regions of electron density are forced closer together, so the octahedral angles are smaller and uniform. ✓ The difference comes from five versus six regions of electron density around the sulfur: trigonal bipyramidal (90° and 120°) versus octahedral (all 90°). ✕
Naming the electron geometry instead of the shape
SF₄ has trigonal bipyramidal electron geometry but its shape is seesaw. The question asks for the shape, which counts atoms only. Give the geometry when it asks about bond angles, and the shape when it asks to name the shape.