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Intermolecular Forces

Intermolecular forces


So intermolecular forces what are they all about?! In plain English, intermolecular forces are the smaller forces in a bigger equation and are simply forces between molecules.

You can get a range of different bonds, the main ones we know are ionic and covalent bonds which are very strong when compared to these little intermolecular forces in between molecules. There are three different intermolecular forces you deal with at A level and trust me these little guys will become the bane of your life.

These three types of bonds are known as hydrogen bonding, permanent dipoles and temporary dipoles.

Hydrogen bonding

Hydrogen bonding is the strongest type of intermolecular force and occurs in molecules containing a O-H, N-H or F-H bonds, this is due to oxygen, nitrogen and fluorine being the most electronegative elements which then creates something known as a dipole. These dipoles exist as delta negative and delta positive and refers the the distribution of electrons across a whole molecule.

Image result for dipole o-h
As seen in the diagram above oxygen has made a sort of association with that of the hydrogen and this occurs because oxygen has a lone pair of electrons. This creates a hydrogen bond with the hydrogen of another molecule. This diagram is just the tip of the ice burg (water puns!), hydrogen bonding occurs between many molecules of water resulting in a huge pool of hydrogen bonds.

Hydrogen bonding with water can cause a multitude of interesting properties including:

- Ice being less dense than water
- Water having a relatively high melting and boiling points compared to molecules which have permanent dipoles.
- Water has a relatively high surface tension which allows small insects to 'float' and walk across a raft of hydrogen bonds.

Permanent dipoles

Permanent dipoles occur when there are polar bonds and as it practically says on the tin there are dipoles and guess what? They are permanent! 

Dipoles become permanent due to large differences in electronegativity like those we saw in the hydrogen bonds. These dipoles create a slightly positive and a slightly negative end and can shift electrons in non-polar molecules due to this slight charge difference. 

Image result for permanent dipole

Temporary dipoles

This intermolecular force is unique as these forces occur randomly due to the movement of electrons in the atoms shells. This movement can change the distribution of the charge temporarily resulting in an instantaneous dipole which induces dipoles in neighboring molecules. These induced dipoles attract one another resulting in an intermolecular force. The size of this force increases as the number of electrons increase which in turn will increase in boiling point as there are more forces to break and thus more energy will be needed.

Did you find this helpful? Feel free to drop a comment and let me know what you liked and if I have missed something!

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