Physical Properties of Covalent Compounds - Macromolecular compounds

Macromolecular Compounds


  1. The macromolecular compounds have giant, covalent molecules with extremely large molecular lattices.
  2. They have very high melting and boiling points.
  3. They don't conduct electricity — not even when molten (except for graphite).
  4. They're usually insoluble in water.
  5. Examples of such macromolecules are diamond, silica and graphite.


Diamond and Silica(Sand)

(3 dimensional structure macromolecular compound - Diamond)


  1. A diamond crystal or a grain of sand is just one giant molecule. Such molecules, because they are so rigid and strong, have very high melting points.
  2. Each carbon atom forms four covalent bonds in a very rigid giant covalent structure, which makes diamond the hardest natural substance. This makes diamonds ideal as cutting tools.
  3. All those strong covalent bonds give diamond a very high melting point.
  4. It doesn't conduct electricity because it has no free electrons.
  5. Diamond is an allotrope of carbon. Allotropes are different forms of the same element in the same physical state


Graphite

(3 dimensional layer structure: graphite)


  1. Carbon also occurs in the form of graphite. The carbon atoms form joined hexagonal rings forming layers 1 atom thick.
  2. Graphite is black and opaque.
  3. Each carbon atom only forms three covalent bonds, creating sheets of carbon atoms which are free to slide over each other. This makes graphite slippery, so it's useful as a lubricant.
  4. The layers are held together so loosely that they can be rubbed off onto paper to leave a black mark — that's how pencils work.
  5. Graphite has a high melting point — the covalent bonds need lots of energy before they break.
  6. Only three out of each carbon's four outer electrons are used in bonds, so there are lots of spare electrons. This means graphite conducts electricity — it's used for electrodes.


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