State the structure & properties of ionic compounds.
Giant ionic lattice structure
- high mp/bp
- (mostly) soluble in water and insoluble in organic solvents
- cannot conduct electricity in solid state but can conduct when molten or aqueous
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State the structure & properties of covalent compounds.
Simple molecular structure
- low mp/bp
- soluble in organic solvents but insoluble in water
- cannot conduct electricity in all states
Exception: substances that can form ions when dissolved in water (e.g. HCl and NH3) can conduct when aqueous
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State the structure & properties of diamond, graphite & sand.
Giant molecular structure
- high mp/bp
- insoluble in organic solvents but insoluble in water
- cannot conduct electricity in all states
Exception: graphite can conduct.
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Explain why ionic compounds have high mp.
- giant ionic lattice structrure
- a lot of energy required to overcome the strong electrostatic forces of attraction between ions.
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Explain why covalent compounds have low bp.
- simple molecular structure
- little energy required to overcome the weak intermolecular forces of attraction between molecules.
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Explain why diamond, graphite and sand have high mp.
- giant molecular structrure
- a lot of energy required to break the numerous strong covalent bonds between atoms.
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Explain why ionic compounds can conduct electricity when aq or molten but not when solid.
When solid, the ions are held in fixed positions by strong electrostatic forces of attraction; no free ions to carry charge.
When molten or aq, the electrostatic forces of attraction have been overcome; ions are mobile and free to carry charge.
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Explain why covalent compounds cannot conduct electricity.
- simple molecular structure
- no free mobile electrons or ions to carry charge
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Explain why diamond cannot conduct electricity but graphite can conduct electricity.
In diamond, all the electrons are used in bonding; no free electrons to act as charge carriers.
In graphite, each C atom is bonded to 3 other C atoms; each C atom has 1 free electron to act as charged carriers.
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Explain why diamond is hard but graphite is soft & slippery.
In diamond, there is network of strong covalent bonds which require a lot of energy to break.
In graphite, there is weak IMF of attraction between 2D layers; layers can easily slide when a force is applied
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