Covalent Substances: Two Kinds

Substances with covalent bonds (electron Sharing) can either be simple molecules or giant structures
Simple Molecular Substance
1. The atom forms a very strong covalent bond to form small molecules of several atoms.
2. By contrast, the forces of attraction between these molecules are very weak
3. The result of these feeble intermolecular forces
  1. The melting and boiling point are very low
  2. Because molecules are easily parted from each other.
4. It’s the intermolecular forces that get broken when simple molecular substances melt or boil – not the much stronger covalent bonds.
5. Most molecular substances are gases or liquids at room temperature but they can be solids
6. Molecular substances don’t conduct electricity – there are not ions so there’s no electrical charge.
Giant covalent Structure are macromolecules
1. These are similar to giant ionic Structure (lattice)
  1. Except that there are no charged ions
2. All the atoms are bonded to each other by strong covalent bonds
  1. This means that they have a very high melting and boiling points
3. They don’t conduct electricity - not even when molten (except for graphite)
  1. The main example are diamond and graphite as they are both made only from carbon atoms and silicon atoms (Silica)
4. Diamond
  1. Each carbon atom forms four covalent bonds in a very rigid giant structure
    1. Made of the hardest natural substance
      1. Used for drill tips and it’s pretty and sparkly too
5. Silicon Dioxide (Silica)
  1. This is what sand made of - each grain of sand is one giant structure of silicon and oxygen.
6. Graphite
  1. Each carbon atom only forms three covalent bonds
  2. These creates layers which are free to slide other each other (like a pack of cards) - Graphite is soft and slippery
  3. This is because there are weak intermolecular forces between the layers

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Covalent Substances: Two Kinds

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	Created by Evangeline Taylor over 10 years ago