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Bonding in solids – identify unknowns from their properties

ChemistryChemical BondingAges 15–16

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A virtual lab for working out the bonding in unknown solids from their properties. Heat each sample to estimate its melting point, test its solubility in water and in hexane, test whether the solid, the melt and the solution conduct electricity, and strike it with a hammer to see whether it is malleable or brittle. Fill in a property table, classify each substance as ionic, simple molecular, metallic or giant covalent with a reason, then check your answers to see real data and a particle-level picture.

Lesson: Structure and bonding: properties of ionic, molecular, metallic and giant covalent substances

What it shows

The properties of a solid depend on its particles and the forces between them. Ionic compounds such as sodium chloride form giant lattices of ions: they melt at high temperatures and conduct only when molten or dissolved, when the ions can move. Simple molecular substances such as sugar and wax have weak forces between their molecules, so they melt easily and never conduct. Metals conduct as solids because of their delocalised electrons and can be hammered flat. Giant covalent substances such as sand do not melt in the lab; graphite is the exception that conducts.

How to use

Choose a Sample and a Test, then press the step button, for example Heat, or Add sample and then Shake. For heating and the melt test, choose the Bunsen burner or the electric furnace as the Heat source. Record each result with the buttons below the steps. For every unknown, choose its Type of substance and a Reason, then press Check. Identified samples show their real data and a particle picture.

Parameters you can change

  • Mode Unknown substances (random), Known substances (practice)
  • Starting test Heating (melting point), Solubility in water, Solubility in hexane, Conductivity: solid, Conductivity: melt, Conductivity: aqueous solution, Hammer test (malleable or brittle)
  • Heat source Bunsen burner (to about 600 °C), Electric furnace (to 1100 °C)
  • Number of unknown substances 2–5 samples
  • Describe observations in words

Questions to explore

  1. Why does sodium chloride conduct electricity when molten or dissolved but not as a solid?
  2. Sugar dissolves well in water. Why does this not show that sugar is an ionic compound?
  3. Graphite conducts as a solid. Which test results show that graphite is not a metal?

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