Topic 2a - Simple Molecular Substances

Simple molecules

Trends in melting and boiling points

Properties of simple molecules

Made up of only a few atoms joined by covalent bonds

Hydrogen - H2

Oxygen - O2

Chlorine - Cl2

Ammonia - NH3

Hydrogen chloride - HCl

Methane - CH4

Water - H2O

Nitrogen - N2

Electrical conductivity

Don't conduct electricity in any state

Melting and boiling points

Low melting and boiling points

Although atoms form very strong covalent bonds the forces of attraction between molecules is very weak (intermolecular forces)

And it's the intermolecular forces that need to be broken

As molecules get bigger the strength of the intermolecular forces increase so more energy is needed to break them

So boiling points increase the bigger the molecule