Structures and properties C2 AQA

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  • Created on: 08-04-10 19:56
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Structures and properties
Ionic compounds:
It takes a lot of energy to break the bonds which hold a giant
ionic lattice together. So ionic compounds have very high
melting points ­ they are all solids at room temperature. Also,
ionic compounds will conduct electricity when we melt them or
dissolve them in water because their ions can then move freely.
Simple molecules:
Substances made up of simple molecules have low melting and
boiling points. The forces between simple molecules are small.
These weak intermolecular forces explain the low melting points
and boiling points. Simple molecules have no overall charge, so
they cannot carry electrical charge. Therefore substances
containing simple molecules do not conduct electricity.
Giant Covalent Substances:
Some covalently bonded substances contain giant structures.
These substances have high melting points and boiling points.
The giant structure of graphite contains layers of atoms that can
slide over each other which make graphite slippery. The atoms
in diamond have a different structure and cannot slide like this ­
so diamond is a very hard substance. Graphite can conduct
electricity because of the delocalized electrons along its layers.
Giant metallic structures:
We can bend and shape metals because the layers of atoms (or
ions) in a metal can slide over each other. Delocalised electrons
in metals allow them to conduct heat and electricity well.

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