Properties of Simple Molecules (Oxford AQA IGCSE Chemistry)

Melting & Boiling Points of Simple Molecules

• Substances that consist of simple molecules are gases, liquid or solids with relatively low melting and boiling points 

• They have strong covalent bonds between the atoms, but only weak forces between molecules

Diagram to show the difference between covalent and intermolecular bonds

• They have relatively low melting and boiling points because: 

  • There are weak intermolecular forces between the molecules

  • These forces require little energy to overcome 

• As the molecules increase in size, the melting and boiling points generally increase because the strength of these intermolecular forces increases and so more energy is needed to break them 

Conductivity of Simple Molecules

Simple molecules are poor conductors of electricity (even when molten) because:

• There are no free ions or electrons to move and carry the charge.

• Most covalent compounds do not conduct at all in the solid state and are thus insulators

• Common insulators include the plastic coating around household electrical wiring, rubber and wood