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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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Ionic Compounds

  • 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.
  • Insoluble.
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