CIE IGCSE Chemistry

Revision Notes

3.3.2 Molecules & Compounds

Extended Only

Electron Arrangement in Complex Covalent Molecules


Dot & cross Nitrogen, IGCSE & GCSE Chemistry revision notes 

C2H4 (ethene):

Dot-&-cross-Ethene_, IGCSE & GCSE Chemistry revision notes 

CH3OH (methanol):

Dot & cross Methanol, IGCSE & GCSE Chemistry revision notes



Dot-&-cross-Carbon-Dioxide_, downloadable IGCSE & GCSE Chemistry revision notes

Extended Only

Melting & Boiling Points of 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
  • 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

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.

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