Molecular geometry practice: test VSEPR shapes and bond angles

Q: What’s the quickest way to avoid mixing up electron-domain geometry and molecular geometry?

Force a two-label habit: first write the steric number and the electron-domain geometry (linear/trigonal planar/tetrahedral/trigonal bipyramidal/octahedral). Then write the AXE pattern and name the molecular geometry after removing lone-pair positions (for example, SN = 4 with AX 3 E is trigonal pyramidal, not tetrahedral).

Q: How do I decide whether a bond angle should be reported as 109.5°, “<109.5°,” or a specific value like 107°?

On AP Chemistry and most Gen Chem I exams, you’re usually expected to give ideal angles (109.5°, 120°, 180°, 90°) or directional deviations (e.g., NH 3 has angles slightly less than 109.5° due to one lone pair). Exact experimental angles (like ~107° for NH 3 ) are rarely required unless explicitly stated.

Q: Why do lone pairs go equatorial in trigonal bipyramidal structures?

Equatorial positions in a trigonal bipyramidal arrangement have fewer 90° interactions than axial positions. Because lone pairs repel more strongly than bonding pairs, placing a lone pair equatorial minimizes strong 90° repulsions, which is why AX 4 E becomes seesaw and AX 3 E 2 becomes T-shaped when the electron-domain geometry is trigonal bipyramidal.

Q: Do resonance structures change the predicted VSEPR shape?

Typically, no. Resonance changes how electrons are distributed among equivalent bonding descriptions, but it usually does not change the number of electron domains around the central atom, so the electron-domain geometry and molecular geometry predicted by VSEPR remain the same. Focus on domain count, not the “location” of a particular double bond in resonance drawings.

Q: When does VSEPR stop working well?

VSEPR is most reliable for common main-group molecules and polyatomic ions where a clear central atom and localized electron domains make sense. It becomes less predictive for many transition-metal complexes and for cases where bonding is highly delocalized or where d-orbital effects dominate; those topics are usually handled with coordination chemistry models rather than introductory VSEPR rules.

12 – 65 Questions 13 min

This quiz targets molecular geometry in general chemistry, using VSEPR theory to predict 3D shapes and approximate bond angles from Lewis structures. Expect AP Chemistry and General Chemistry I depth: assign steric number and AXE notation, distinguish electron-domain vs molecular geometry, and explain angle deviations from lone pairs and multiple bonds.

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1What is the molecular geometry around carbon in CO2?

2In VSEPR counting, a double bond counts as one electron group (one region of electron density) on the central atom.

True / False

3Which AXE notation matches NH3 (ammonia) around nitrogen?

4What is the molecular geometry of H2O around oxygen?

5In a trigonal bipyramidal electron-domain geometry, lone pairs prefer axial positions to minimize repulsions.

True / False

6What AXE notation best describes SO2 around sulfur (ignoring resonance details but using the correct electron-group count)?

7A central atom with three electron groups has trigonal planar electron-domain geometry.

True / False

8What is the ideal bond angle for a trigonal planar electron-domain geometry?

9Select all that apply. Which statements are correct for counting electron groups on a central atom in VSEPR?

Select all that apply

10Sulfur tetrafluoride (SF4) has 5 electron groups around S (4 bonds and 1 lone pair). What is its molecular geometry?

11Arrange the steps for predicting a molecule’s molecular geometry using VSEPR (first step to last step).

Put in order

1Count electron groups on the central atom

2Assign the electron-domain geometry

3Derive the molecular geometry by ignoring lone-pair positions

4Draw a valid Lewis structure

12What is the ideal bond angle in a tetrahedral electron-domain geometry?

13CF4 has polar C–F bonds. What is the overall polarity of CF4?

14Select all that apply. For a trigonal bipyramidal electron-domain geometry (steric number 5), which statements are true?

Select all that apply

15Arrange the electron-domain geometries in order of increasing steric number (2 to 6).

Put in order

1Octahedral

2Tetrahedral

3Linear

4Trigonal planar

5Trigonal bipyramidal

16Compared with CH4, the H–N–H bond angle in NH3 is:

17Select all that apply. In an ideal trigonal bipyramidal molecule such as PF5, which bond angles are present?

Select all that apply

18In the carbonate ion, CO3^2−, how many electron groups surround the central carbon?

19Which molecule is expected to have the smallest bond angle around its central atom?

20Chlorine trifluoride (ClF3) has 5 electron groups around Cl (3 bonds and 2 lone pairs). What is its molecular geometry?

21Arrange these molecules from largest to smallest typical bond angle around the central atom: CH4, NH3, H2O, BF3, CO2.

Put in order

1H2O

2BF3

3NH3

4CO2

5CH4

22A lab partner draws SOCl2 (thionyl chloride) with S double-bonded to O, single-bonded to two Cl, and with one lone pair on S. What is the molecular geometry around sulfur?

23Select all that apply. With identical outer atoms, which molecular geometries can be nonpolar due to dipole cancellation?

Select all that apply

24The nitrate ion, NO3−, has trigonal planar molecular geometry about nitrogen.

True / False

25XeF2 is often written as AX2E3 around Xe. What is the molecular geometry?

Frequent VSEPR Shape + Bond Angle Errors (and Reliable Fixes)

Most missed VSEPR questions come from skipping a careful electron-domain count or naming the geometry too early. Use the checks below to catch the high-frequency traps.

1) Counting bonds instead of electron domains

Mistake: Treating a double/triple bond as “two/three groups.”
Fix: In VSEPR, any bond (single, double, triple) counts as one region of electron density on the central atom. Count domains, not bond order.

2) Confusing electron-domain geometry with molecular geometry

Mistake: Calling NH₃ “tetrahedral” or H₂O “tetrahedral.”
Fix: Do it in two steps: (i) electron-domain geometry from steric number, then (ii) molecular geometry after “hiding” lone-pair positions.

3) Misreading the central atom in polyatomic ions

Mistake: Letting terminal atoms (and their lone pairs) drive the shape name.
Fix: VSEPR geometry is defined around the central atom only. Terminal lone pairs affect polarity discussions but do not change the central atom’s domain count.

4) Placing lone pairs in the wrong positions for trigonal bipyramidal (SN = 5)

Mistake: Putting lone pairs axial “because it looks symmetric.”
Fix: Lone pairs prefer equatorial sites (fewer 90° interactions). This is the difference between correctly naming seesaw (AX₄E), T-shaped (AX₃E₂), and linear (AX₂E₃).

5) Treating ideal angles as exact numbers

Mistake: Reporting 109.5° for any AX₄-based shape.
Fix: Use ideal angles as baselines, then adjust qualitatively: lone pairs compress adjacent bond angles; multiple bonds can slightly widen angles to other domains.

6) Assuming “polar bonds” automatically means “polar molecule”

Mistake: Declaring CO₂ or SF₆ polar due to bond polarity.
Fix: After finding the shape, check symmetry and cancellation of bond dipoles; symmetric shapes with identical surrounding atoms often sum to ~0.

VSEPR Geometry: 5 High-Impact Rules to Apply Under Exam Time Pressure

Use these five rules as your default workflow whenever a Lewis structure is provided (or must be drawn) and you’re asked for a shape or bond angle.

Lock in the steric number from the central atom before naming anything. Count electron domains around the central atom as: each bond (single/double/triple) = 1 domain, each lone pair on the central atom = 1 domain. The steric number determines the electron-domain geometry (2 linear, 3 trigonal planar, 4 tetrahedral, 5 trigonal bipyramidal, 6 octahedral).
Translate to AXE notation to prevent “chart-memorization” errors. Write A = central atom, X = number of bonded atoms (domains that are bonds), E = number of lone pairs on the central atom. Then map AXE to the molecular geometry name (for example, AX₃E = trigonal pyramidal; AX₂E₂ = bent).
Separate “electron-domain geometry” from “molecular geometry” every time. If E > 0, the electron-domain geometry and molecular geometry differ. State (even mentally) both: it keeps you from calling NH₃ tetrahedral (it’s tetrahedral EDG, trigonal pyramidal MG) and from missing that H₂O is bent even though the domains are tetrahedral.
Use ideal angles as anchors, then reason directionally about deviations. Start from 180°, 120°, 109.5°, 90°/120° (SN = 5), and 90° (SN = 6). Then apply the repulsion hierarchy: lone pair–lone pair > lone pair–bond > bond–bond, so lone pairs typically compress bond angles; higher electron density (often near multiple bonds) can slightly widen competing angles.
For SN = 5 and SN = 6, place lone pairs strategically before deciding the final name. In trigonal bipyramidal arrangements, put lone pairs in equatorial positions first; in octahedral arrangements, lone pairs spread out (often opposite when possible) to minimize lone pair–lone pair repulsion. Correct lone-pair placement is what distinguishes seesaw vs T-shaped vs linear (SN = 5) and square pyramidal vs square planar (SN = 6).

Authoritative VSEPR + Molecular Geometry References (Free and Instructor-Trusted)

OpenStax Chemistry 2e, 7.6: Molecular Structure and Polarity — Clear VSEPR workflow from Lewis structures, including common shapes and approximate bond angles.
Khan Academy: Molecular geometry (VSEPR theory) — Visual explanation of electron domains vs molecular geometry with bond-angle intuition.
Chemistry LibreTexts: VSEPR – Molecular Geometry — Detailed tables, AXE patterns, and worked examples that mirror Gen Chem exam expectations.
Davidson College: VSEPR Model (Virtual Chemistry Experiments) — Interactive practice mapping Lewis structures to shapes and angles.
University of Oxford: Virtual Chemistry (VSEPR) — 3D-focused overview of common molecular shapes and how electron-pair repulsion drives geometry.

VSEPR Molecular Geometry FAQ: AXE Notation, Lone Pairs, and Angle Reasoning

Do double and triple bonds count as more than one electron domain in VSEPR?

No. In VSEPR, a single bond, double bond, or triple bond between the central atom and a terminal atom is treated as one electron domain (one region of electron density). However, multiple bonds often carry higher electron density, so they can slightly shift nearby bond angles compared with the ideal values.

What’s the quickest way to avoid mixing up electron-domain geometry and molecular geometry?

Force a two-label habit: first write the steric number and the electron-domain geometry (linear/trigonal planar/tetrahedral/trigonal bipyramidal/octahedral). Then write the AXE pattern and name the molecular geometry after removing lone-pair positions (for example, SN = 4 with AX₃E is trigonal pyramidal, not tetrahedral).

How do I decide whether a bond angle should be reported as 109.5°, “<109.5°,” or a specific value like 107°?

On AP Chemistry and most Gen Chem I exams, you’re usually expected to give ideal angles (109.5°, 120°, 180°, 90°) or directional deviations (e.g., NH₃ has angles slightly less than 109.5° due to one lone pair). Exact experimental angles (like ~107° for NH₃) are rarely required unless explicitly stated.

Why do lone pairs go equatorial in trigonal bipyramidal structures?

Equatorial positions in a trigonal bipyramidal arrangement have fewer 90° interactions than axial positions. Because lone pairs repel more strongly than bonding pairs, placing a lone pair equatorial minimizes strong 90° repulsions, which is why AX₄E becomes seesaw and AX₃E₂ becomes T-shaped when the electron-domain geometry is trigonal bipyramidal.

Do resonance structures change the predicted VSEPR shape?

Typically, no. Resonance changes how electrons are distributed among equivalent bonding descriptions, but it usually does not change the number of electron domains around the central atom, so the electron-domain geometry and molecular geometry predicted by VSEPR remain the same. Focus on domain count, not the “location” of a particular double bond in resonance drawings.

When does VSEPR stop working well?

VSEPR is most reliable for common main-group molecules and polyatomic ions where a clear central atom and localized electron domains make sense. It becomes less predictive for many transition-metal complexes and for cases where bonding is highly delocalized or where d-orbital effects dominate; those topics are usually handled with coordination chemistry models rather than introductory VSEPR rules.