Physical properties from structure
Introduced| English | Meaning |
|---|---|
| conductivity/kɒndəkˈtɪvɪti/ | conductivity |
| solubility/ˌsɒljuːˈbɪlɪti/ | The maximum amount of a solute that can dissolve in a specified amount of solvent at a given temperature and pressure. |
| molten/ˈməʊltn/ | In the liquid state after being melted by heating. |
| soluble/ˈsɒljuːbl/ | Able to dissolve in a specified solvent under the stated conditions. |
| insoluble/ɪnˈsɒljuːbl/ | Having very low solubility in a specified solvent under the stated conditions. |
Structure decides everything
- The structure decides a substance's physical properties.
- Melting point, conductivity 电导率 and solubility 溶解度 all follow from the bonding.
- You can even work backwards to identify an unknown.
Structure-property lab
Link a material property to the structure that causes it.
Simple molecular substances have low melting points because their covalent bonds are weak.
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False. The covalent bonds inside the molecules are strong. Melting only overcomes the weak forces between molecules, which is why the melting point is low.
Melting and boiling points
- High when strong forces (ionic, covalent or metallic) must be broken.
- Low when only weak intermolecular forces break (simple molecular).
Quartz is a giant covalent structure of silicon and oxygen
A substance has a high melting point when:
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Breaking strong bonds needs lots of energy, giving a high melting/boiling point; weak forces give a low one.
Match each structure to its properties.
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Properties come from structure: strong giant lattices melt high; simple molecules melt low.
Conductivity and solubility
- Conductivity needs charged particles that can move:
- ionic solids conduct only when molten 熔融 or dissolved (ions free);
- metals conduct (delocalised electrons); graphite conducts too.
- Solubility: ionic solids are usually soluble 可溶 in water; molecular and giant-covalent solids are usually insoluble 不溶.
An ionic solid conducts electricity:
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The ions are fixed in the solid lattice; only when molten or dissolved can they move and carry charge.
Graphite conducts electricity because:
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Graphite has delocalised electrons between its layers, so it conducts even though it is a non-metal.
Identifying an unknown
- From a substance's melting point, conductivity and solubility, you can deduce its structure and bonding.
A solid with a very high melting point that does not conduct and is insoluble is most likely:
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Very high mp + no conductivity (not graphite) + insoluble points to a giant covalent network like diamond or SiO₂.
You've got it
- high mp/bp = strong forces (ionic/covalent/metallic); low = weak intermolecular (simple molecular)
- conduct: ionic only when molten/dissolved; metals + graphite always
- ionic usually soluble; molecular & giant covalent insoluble
- use mp + conductivity + solubility to identify the structure