Molecules and Compounds

Electron Arrangement in Complex Covalent Molecules

Nitrogen:

C₂H₄ (ethene):

CH₃OH (methanol):

CO₂:

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