Overview
Suitable for: GCSE and A-level Chemistry.
Prior knowledge: Students should understand the charges of protons and electrons, the structure of an atom and basic electron arrangements.
Use the simulation for teacher-led explanation, paired investigation or revision. The five screens link electron transfer, ion charges, chemical formulae, giant ionic structures and observable properties.
Suggested teaching sequence
- Start with the formation of ions
Choose sodium chloride in the Electron transfer screen. Use All shells to establish the starting electron arrangements, then ask students to predict how losing or gaining one electron will affect each atom’s charge.
Select Next electron to animate one transfer and pause. Inspect the sodium and chloride ions, comparing their proton and electron numbers. Emphasise that the nuclei remain unchanged.
Switch to Outer electrons to connect the model to the simplified dot-and-cross diagrams used in textbooks and exam questions.
- Compare different transfer patterns
Work through MgO → MgCl₂ → Na₂O. Before each animation, ask students to predict how many electrons must be transferred and how many atoms of each element are required.
- MgO: one magnesium atom transfers two electrons to one oxygen atom.
- MgCl₂: one magnesium atom transfers one electron to each of two chlorine atoms.
- Na₂O: two sodium atoms each transfer one electron to one oxygen atom.
All three examples involve two transferred electrons, but their ion ratios differ. Ask students to explain each ratio using the charges formed.
- Build the formula from the charges
Open Build the formula and use Use transfer example to load the current element pair.
Change the number of each ion using the plus and minus controls. Ask students to make the total charge zero, then check whether their numbers give the smallest whole-number ratio.
Use Hide formula for prediction and Find simplest ratio to reveal the answer. A useful discussion is: “Why do we write MgO rather than Mg₂O₂, even though both ratios balance the charges?”
- Connect the formula to a giant lattice
Open Giant lattice and compare One layer with the 3D lattice. Highlight the nearest neighbours and rotate the model.
Explain that an interior ion in sodium chloride has six nearest neighbours of the opposite charge. A single flat layer shows only four; the other two lie outside that plane.
Use this to establish that NaCl represents a repeating 1:1 ratio throughout a giant structure. It does not describe separate sodium chloride molecules or permanently paired donor and acceptor ions.
- Explain the properties
Use the four Properties views to connect observations to particles:
- Melting: increase the energy input and observe the loss of order. The particles remain charged ions, which can move past one another in the liquid.
- Conductivity: switch on the supply and compare solid, molten and aqueous sodium chloride. Ask students to identify both the charged particles and whether they can move.
- Brittleness: shift the layers until like charges become adjacent. Link the resulting repulsion to fracture.
- Dissolving: follow ions leaving the crystal and use the hydration zoom to compare water orientation around Na⁺ and Cl⁻. Discuss why solubility varies between ionic compounds.
- Check understanding
Use Explain & check to practise reading dot-and-cross diagrams, identifying ion charges, counting transferred electrons and deducing formulae.
The Discuss & explain section provides prompts and revealable key points. Students can compare their explanations with these points; written discussion responses are not automatically marked.
A-level extension
Select A-level to explore three-electron and six-electron examples, including AlF₃, Li₃N, Al₂O₃ and Mg₃N₂.
Use the atom-to-ion equations to link electron loss with oxidation and electron gain with reduction. Extend formula building to intact polyatomic ions, including nitrate, sulfate, carbonate, hydroxide and ammonium.
The Attraction lab compares the effects of ionic charge and separation on electrostatic attraction. Use the accompanying explanations to introduce the roles of ionisation, lattice formation and hydration. These are qualitative models rather than full thermochemical calculations.
Key teaching points and model limits
- Electron transfer forms ions. Ionic bonding is the electrostatic attraction between oppositely charged ions.
- Dots and crosses show electron origins; all electrons are identical.
- A neutral compound still contains individually charged ions.
- The outer-electron view omits filled inner shells. A bracketed metal symbol without electron marks does not mean the ion has lost all its electrons.
- Full outer shells help students predict common ions, but do not provide a complete explanation of the energetics of compound formation.
- Electron paths and intermediate charges are bookkeeping representations, not actual trajectories or stable intermediate products.
- The properties demonstrations use sodium chloride. Avoid assuming every ionic compound has identical solubility or behaviour in water.
Practical controls
Use Next electron to pause after each transfer, or Play all to show the complete sequence. The progress slider and speed controls support discussion and replay. Reset restores the neutral atoms and leaves the animation paused.
Use Projector view for classroom display, Black & white for textbook-style presentation, and Save diagram to export the current electron diagram as an SVG for worksheets or slides.