Teaching focus
Use this tool to help students connect electron arrangements, shared pairs, molecular formulae and the properties of covalent substances. Students should already recognise element symbols and understand simple electron shell arrangements.
The four sections can be used separately across a sequence of lessons.
Suggested teaching sequence
1. Begin with a single shared pair
In Build molecules, choose hydrogen and start with the separate atoms. Ask students how many electrons each atom has before selecting Combine atoms. Use the step buttons, pause control or progress slider to discuss what changes.
Inspect each atom in the completed molecule. Establish that the same shared pair counts towards both atoms’ outer shells, giving each hydrogen atom access to two electrons.
2. Build up to larger molecules
Work through hydrogen chloride, water, ammonia and methane. Ask students to predict how many bonds each atom will form before combining them. Use Check outer shells and click individual atoms to identify shared and unshared electrons.
Useful prompts include:
- How many electrons does each atom contribute to the shared pairs?
- Which electrons count towards this atom’s completed outer shell?
- How many lone pairs remain?
- Why does oxygen form two bonds in water?
3. Compare single, double and triple bonds
Open Why a bond forms and click the cards to compare hydrogen, oxygen and nitrogen. Count the shared pairs and remaining lone pairs in each diagram. Establish that single, double and triple bonds contain one, two and three shared pairs respectively.
Select Show the attractions and ask students to identify the charges involved. Develop the explanation that negative shared electrons are attracted to both positive nuclei. A completed outer shell is a useful pattern; the electrostatic attraction explains what holds the atoms together.
4. Connect diagrams with formulae
Use Hide formula before asking students to count the atoms and write the molecular formula. Switch between Dot & cross and Displayed formula to connect the representations.
Emphasise that a subscript gives the number of atoms of an element, while each bond line represents one shared pair of electrons. Carbon dioxide and ethene provide useful examples containing double bonds.
5. Link structure to properties
In Structures & properties, begin with small molecules and use Heat: separate molecules. Ask students to describe what happens to the molecules and the attractions between them.
Compare this with diamond’s continuous network and graphite’s layered structure. Use Slide the layers to support explanations of graphite’s softness. Extend to graphene, silicon dioxide, fullerenes and polymers as appropriate.
Encourage explanations that follow the sequence: structure → bonds or forces → energy or movement → property.
6. Check understanding
Use Read the diagram as a mini-whiteboard activity, paired task or independent check. Students enter the molecular formula, total shared pairs and total lone pairs, then select Check answers.
Remind students that the pair counts refer to the whole molecule. Ask them to explain any corrections using the diagram before moving to another example.
Key teaching reminders
- Dots and crosses identify the atoms that supplied the electrons. All electrons have the same negative charge.
- Shared electrons count towards the outer shells of both bonded atoms.
- Shell circles represent energy levels. The diagrams simplify molecular shapes, sizes and electron behaviour.
- The bonding animation models electron sharing; it does not show a reaction mechanism.
- When a simple molecular substance melts or boils, intermolecular forces are overcome and the molecules remain intact.
Useful classroom controls
Use Projector view to enlarge the molecule builder, Inner shells to reconnect bonding with electron arrangements, and Black & white to practise interpreting diagrams without colour cues. Save diagram exports an SVG for worksheets or slides.
The builder supports 14 selected molecules. Ethyne is included as an extension example.