Learning objectives
Students should be able to:
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Describe simple molecular solids as discrete covalently bonded molecules held together by intermolecular attractions.
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Explain melting and boiling in terms of overcoming intermolecular forces.
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Explain water’s relatively high melting and boiling points and the lower density of ice.
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Relate solubility to interactions between solute and solvent particles.
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Explain electrical conductivity through the presence or absence of mobile charged particles.
Suggested teaching sequence
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Molecular lattices: Compare iodine and ice. Hide and reveal attractions to distinguish covalent bonds within molecules from forces between molecules. Rotate and tilt the larger ice lattice, then switch to the local view to inspect hydrogen bonding around one water molecule.
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Melting & boiling: Ask students to predict which bonds or attractions change. Follow an intact molecule through the solid, liquid and gas stages. Pause during boiling to identify vapour bubbles forming within the liquid and releasing molecules at the surface.
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Ice & water: Run the 2-D ice-to-liquid animation and compare the equal-mass volume readouts. Ask students to explain why closer packing increases density and why ice floats. Use the separate 3-D views to revisit the open structure.
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Water’s anomaly: Examine the other Group 16 hydrides before revealing water. Compare melting and boiling points, distinguishing the general boiling-point trend from water’s hydrogen-bonding anomaly.
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Solubility: Investigate ethanol in water, hexane in water, and iodine in water or hexane. Students should predict the outcome before playing the animation. Follow original attractions being disrupted and new contacts forming, then connect the molecular model to the bulk observation.
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Conductivity: Compare neutral molecular samples with aqueous HCl. Follow the initially mixed H⁺ and Cl⁻ ions towards opposite electrodes, then reverse polarity. Distinguish ion movement in the solution from electron movement in the wires.
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Check understanding: Use the questions and explanatory feedback for consolidation, discussion or independent review.
Teaching tips and misconceptions
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Melting and boiling do not break the covalent bonds within these molecules.
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Boiling bubbles contain the substance’s vapour, not air or separate constituent elements.
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Ice is a molecular solid, not a giant covalent structure. Liquid water still contains hydrogen bonds.
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Distinguish the bent shape of one water molecule from the approximately tetrahedral arrangement of neighbouring molecules in ice.
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“Like dissolves like” is a useful guide rather than a universal rule. Low solubility is not the same as complete insolubility.
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Dissolving does not automatically produce ions: ethanol solution and aqueous HCl provide a useful contrast.
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H⁺(aq) is shorthand for hydrated hydrogen ions. Pure water has a very small conductivity rather than exactly zero.
Display and independent use
Use Focus view or full screen for projection. Play, pause, step, reset and progress controls allow students to inspect changes at their own pace. Encourage a predict–observe–explain approach, keeping explanations hidden until students have discussed or recorded their ideas. The HTML works offline; external source links require internet access.
Model limitations and practical safety
Particle sizes, spacing, timings and mixture proportions are illustrative. The 2-D water models show selected connections; the 3-D ice models idealise the geometry. The heating sequence is not a quantitative heating curve, and the ice animation does not model water’s density maximum at 4 °C. Conductivity follows ions to the electrodes without modelling electrode reactions.
These are virtual investigations, not practical instructions. Any accompanying laboratory work requires an appropriate school risk assessment: ethanol and hexane are flammable, iodine is harmful, and hydrochloric acid presents concentration-dependent hazards.