Structure detective sim
Heat, test the conductivity, dissolve and hammer eight unknown solids, then decide whether each is giant ionic, simple molecular, giant covalent, metallic or a polymer.
Structure and bonding: deduce the structure from the properties · covers the O-Level, IGCSE, GCSE topic
What the sim shows
The way a substance behaves shows how its particles are held together. Giant ionic (sodium chloride, magnesium oxide): high melting points; no conduction as a solid, because the ions are fixed, but conduction when molten or dissolved, when they can move; brittle. Simple molecular (sulfur, wax, glucose): low melting points, because only weak forces between molecules must be overcome; no conduction. Giant covalent (graphite, silicon dioxide): very high melting points, because many strong covalent bonds must break; insoluble; graphite alone conducts, through delocalised electrons that move along its layers, and weak forces between its layers let them slide. Metallic (copper): conducts as a solid and when molten, through delocalised electrons; malleable. Polymer (poly(ethene)): very long molecules; softens over a range at a fairly low temperature; flexible. Melting points are rounded data-book values: sodium chloride 801 °C, magnesium oxide 2852 °C, sulfur about 115 °C, wax about 55 °C, glucose 146 °C, silicon dioxide about 1710 °C, copper 1085 °C, poly(ethene) softening from about 105 °C; graphite does not melt at normal pressure. Model limits: the furnace has a graphite heating element and is filled with argon, so nothing burns (in air, sulfur, wax, glucose, poly(ethene) and graphite would burn when heated strongly); it reaches 3000 °C, so even magnesium oxide (2852 °C) melts. Above a few hundred °C sulfur boils and wax, glucose and poly(ethene) break down; glucose starts to decompose (caramelise) as it melts; sodium chloride, silicon dioxide and copper boil at 1465, 2950 and 2562 °C. The currents are illustrative; sulfur dissolves only a little in hexane.
- Samples A–H: unknown solids
- Bulb and ammeter: does it conduct?
- Furnace: argon-filled, up to 3000 °C
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