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Atomic Structure

What are the Properties of Simple Molecules?
(compare these with giant molecules and ionic compounds).

When non-metals react with non-metals
a covalently bonded molecule is formed.

Covalent bonds are strong but only exist
between the atoms of the molecule.
The force of attraction between molecules
(called the intermolecular force)
is very weak (compare this with ionic bonding).
The picture below shows the
forces of attraction between two molecules of oxygen gas.

Intermolecular Forces

The weak force between molecules means that very
little energy is needed to separate them. Many
molecular compounds are liquid or gas at room temperature.
They have low melting and boiling points.

Note that when a molecular compound melts or boils,
molecules separate from each other
but the covalent bond between the atoms of the molecule
does not break. The molecule is the same molecule
in the solid, liquid or gas state. If the covalent bond breaks,
the molecule is said to decompose (split up!).

Molecules do not have a charge (no ions) because the
electrons are shared between atoms to form a covalent bond.
Molecular substances will therefore not conduct electricity
(with the exception of graphite which has an unusual structure).

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