Simple Molecular Covalent Substances
- There are strong covalent bonds between the atoms but weak forces between individual molecules.
- They have low boiling and melting points.
- They are liquids are gases at room temperatures or solids but with low melting points.
- No charged particles so don't conduct electricity.
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Giant Molecular Covalent Substances - Diamond
- The covalent bonds in giant molecular covalent substances are strong and so it takes a lot of energy to break these bonds and because of this they have very high melting points.
- They are very hard substances that do not conduct electricity as they have no free electrons.
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Giant Molecular Covalent Substances - Graphite
- High melting point
- Conducts electricity as fourth bond can move freely between layers as it is delocalised so electricity can pass through.
- Very soft - each atom is joined to three others. Layers are held by weak forces and can slide off.
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- High melting and boiling points as the ions are held together by very strong electrostatic forces and so lots of energy is needed to break these bonds.
- Ionic substances are solid at room temperature and must be heated strongly to melt.
- They only conduct when they are molten or dissolved in water because the charged particles can move.
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Uses of Diamond and Graphite
- Diamond is used for cutting tools as it is very hard.
- It is used as a lubricant because forces between layers are weak and layers can slide over each other.
- Graphite has one free electron from each carbon that can move along the layers so graphite conducts electricity and can be used to make electrodes.
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Fractional Distillation of Air
Done to obatain nitrogen and oxygen.
- Gas is cooled to condense it to a liquid - -200 degrees.
- Water vapour condenses and is removed by absorbent filters.
- Carbon dioxide freezes at -79 degrees and is removed.
- Oxygen liquifies at -183 degrees at the bottom of the column.
- Nitrogen liquifies at -196 degrees at the top of the column.
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- Positive ions held together by a sea of delocalised electrons.
- Conducts electricity when solid and liquid as delocalised electrons can move between ions.
- Medium - high melting and boiling points.
- All metals, except mercury, are solid at room temperature.
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