Properties relating to bonding
The properties of elements and compounds can be explained by considering the different types of bonding present inside the molecules.
Ionic lattice
All ionic compounds have a high melting point and boiling point. They conduct when molten or in solution as the ions are free to move.
They can be broken down by electrolysis.
Covalent network
All covalent network structures have very high melting points and boiling points. They are all hard and do not conduct electricity.
Covalent molecular
They have low melting points and boiling points. They do not conduct electricity. Some covalent molecular compounds have higher melting points than expected.
Sometimes two molecules that seem similar can have very different properties because of the intermolecular bonds present. Consider ethanol and ether.
Both molecules have the same molecular formula (C2H6O) yet there is a large difference in boiling points.
Ethanol (CH3CH2OH) is a liquid at room temperature (boiling point 79ËšC).
Ether (CH3OCH3) is a gas at room temperature (boiling point -23ËšC).
Both ethanol and ether have the same molecular mass, however, their melting points and boiling points are different due to the ethanol containing hydrogen bonding.
Ether is a symmetrical molecule, so even though it contains polar bonds, the molecule itself is non-polar and the only intermolecular force present will be weak London dispersion forces.
Ammonia (NH3) and hydrogen fluoride (HF) both also have higher boiling points than might be predicted due to presence of hydrogen bonding between the molecules.