Learning objectives
Students should be able to:
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Count bonding domains and lone pairs around a central atom.
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Distinguish electron-domain arrangement from molecular shape.
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Predict shapes and bond angles using electron-pair repulsion.
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Explain why lone pairs reduce bond angles in ammonia and water.
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Recognise that single, double and triple bonds each occupy one bonding domain.
Using the simulation
1. Shape builder
Choose the number of bonding regions and central lone pairs, or load a real example. Change selected bonds to double bonds to explore the distinction between shared electron pairs and bonding domains.
Rotate the model and toggle lone pairs, angles and the framework. Open the displayed/dot-and-cross comparison to connect the electron diagram with the 3D structure.
Useful starting examples are CO₂, BF₃, CH₄ and SF₆, followed by NH₃ and H₂O.
2. Formula → shape
Use the four explanation stages to establish a consistent approach:
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Count bonding domains and central lone pairs.
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Arrange the domains to minimise repulsion.
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Name the shape formed by the atoms.
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State the bond angles and explain any distortion.
Ask students to predict each stage before advancing. The final stage provides a complete model answer. Use NH₄⁺ to discuss charge and electron counting, and CO₂ or HCN to reinforce how multiple bonds are treated.
3. Shape detective
Choose either 3D → answer or Formula → answer. Students identify bonding domains, lone pairs, total domains, the underlying arrangement, molecular shape and angles.
Check provides feedback and allows corrections; Reveal shows the solution. In formula challenges, the model remains hidden until revealed. Use random selection for mini-whiteboard questions or independent practice. Extension examples can be included when appropriate.
4. Lone-pair lab
Compare CH₄, NH₃ and H₂O. Use Play/Pause, Step, Reset or the slider to explore the change from the ideal tetrahedral angle to the reference angles:
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CH₄: 109.5°
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NH₃: 107°
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H₂O: 104.5°
Ask students to explain why all three have four electron domains but different molecular shapes and bond angles.
Teaching tips and misconceptions
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Count lone pairs on the central atom, not those on surrounding atoms.
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A double bond contains two shared pairs but forms one bonding domain.
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Molecular shape describes atom positions; lone pairs influence the shape but are omitted from its name.
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Reinforce the repulsion order: lone pair–lone pair > lone pair–bonding pair > bonding pair–bonding pair.
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Do not teach a fixed angle reduction per lone pair as a universal rule. Exact angles also depend on the molecule.
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Rotate models to demonstrate that changing the viewpoint does not change the shape. Follow up with students drawing ordinary bonds, solid wedges and dashed wedges.
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Treat generic builder structures as domain models, not proof that a corresponding stable molecule exists.
Extensions and model limitations
Optional examples include trigonal bipyramidal, seesaw, T-shaped, square pyramidal and square planar structures.
Atom colours indicate central and outer roles rather than element identity. Sizes, bond lengths and lone-pair lobes are schematic. Some extension models use ideal parent directions; use the stated angle information rather than measuring the screen.
The lone-pair animation illustrates an explanation, not a molecule physically changing between these states.
Display and independent use
Use Focus view to give the model more space, and Full screen for projection. Models can be rotated by dragging or using the arrow keys.
The same controls support teacher-led discussion and independent practice. Encourage students to write an explanation before checking or revealing answers.