Chemistry - shape of molecules - symmetrical molecules.

Since symmetrical molecules either have no charge(O₂) or have a similar charge on the exterior (CH₄). In either case no attraction or repulsion occurs and it is hard to imagine that a force of attraction actually exists. The fact that we can form solid carbon dioxide(dry ice) and liquid methane is evidence of an intermolecular force of attraction acting between the molecules of each compound.
Such intermolecular forces of attraction are known as dispersion forces or van der waal's forces. Click for a more detailed explanation of how these forces come about.

Symmetry
Symmetrical molecules are also known as non-polar molecules. This means that symmetrical molecules do not have charged poles. In other words non-polar molecules do not have oppositely charged ends. A molecule that can be cut into two identical halves is said to be symmetrical.
	The carbon dioxide molecule on the left is a symmetrical molecule, it does not have oppositely charged ends. The positive charge on the carbon is masked by the negative charges on the oxygen atoms. Click to see an animation of the process
The oxygen atom is also symmetrical with no permanent charge on the molecule.
	A polar molecule such as HCl is not symmetrical. It therefore has two opposite charged ends.
The methane molecule on the right is symmetrical. The negative charge on the carbon is completely surrounded by the positive charges on the hydrogen atoms.The negative carbon is not exposed to the other molecules. Click to see an animation of the process
Since symmetrical molecules either have no charge(O₂) or have a similar charge on the exterior (CH₄). In either case no attraction or repulsion occurs and it is hard to imagine that a force of attraction actually exists. The fact that we can form solid carbon dioxide(dry ice) and liquid methane is evidence of an intermolecular force of attraction acting between the molecules of each compound. Such intermolecular forces of attraction are known as dispersion forces or van der waal's forces. Click for a more detailed explanation of how these forces come about.
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