Forces between molecules

What are intermolecular forces?

The forces of attraction between simple covalent molecules

What are the 3 main type of intermolecular force?

• induced dipole-dipole forces

• Permanent dipole-dipole forces

• Hydrogen bonds

How is a dipole created?

By a difference in charge between 2 atoms caused by a shift in electron density in the bond

Where are permanent forces of attraction found in?

Polar molecules which contain permanent dipoles e.g. propanone

Which hydrocarbon typically has the weakest forms of attraction between molecules?

Alkanes as there are no permanent charges in these molecules

What are induced forces also known as?

Van der waals forces

Which molecules are able to attract each other electrostatically?

Polar molecules which have an overall dipole moment

are intermolecular forces stronger than covalent bonds?

No

What are intermolecular forces significant in explaining?

Higher melting and boiling points

How do permanent dipoles raise the melting and boiling point?

it attracts other molecules, raising the strength of the intermolecular force. this raises mp and bp

How are induced dipole forces formed?

When the movement of electrons in a molecule induces another dipole in another neighbouring dipole. This means molecules will attract each other weakly and as the number of electrons increases so does the strength of the van der waal

What is another factor that can affect the van der Waals forces?

Side chains e.g. methyl groups

Where does hydrogen bonding occur?

Between molecules (intermolecular)

How does hydrogen bonding occur?

In compounds whose molecules consist of a hydrogen atom covalently bonded to an electronegative atom e.g. fluorine. Oxygen or nitrogen. There are slight charges within the molecules caused by a slight shift of electrons in the covalent bond. As a result of these charges, weak electrostatic attractions exist between molecules which are called hydrogen bonds