Comparing Ionic & Covalent Compounds (Edexcel GCSE Chemistry)
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Comparing Ionic & Covalent Compounds
Ionic compounds have high melting and boiling points
This is because the oppositely charged ions in the lattice structure are attracted to each other by strong electrostatic forces which hold them firmly in place
Large amounts of energy are needed to overcome these forces so the m.p. and b.p. are high
Ionic substances can conduct electricity when in either the molten state or when dissolved in solution. In both cases the ions must be able to move and carry the charge
In solid ionic substances the ions are in fixed positions and cannot move, hence they do not conduct electricity
Particles in solution/molten form can move and conduct electricity but in solid form they are in fixed positions and are unable to conduct
Simple covalent substances, such as carbon dioxide and methane, have very strong covalent bonds between the atoms in each molecule, but much weaker intermolecular forces between individual molecules
When one of these substances melts or boils, it is these weak intermolecular forces that break, not the strong covalent bonds
Less energy is needed to break the molecules apart, so they have lower m.p. and b.p. than ionic compounds
They are poor conductors of electricity as there are no free ions or electrons to move and carry 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
Diagram showing the plastic coating surrounding the conducting metal wires in an electric cable
Examiner Tips and Tricks
Simple molecules are small and can be separated into individual units without breaking any bonds.Giant ionic and covalent structures form huge continuous networks of atoms that are bonded together and which cannot be separated into individual units without breaking bonds.
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