1. Properties of Covalent (Molecular) Substances

2. Properties Depend on strength of IMF between “particles” or separate units covalent substances: – units are molecules

3. Intermolecular Forces Dispersion forcesDispersion forces occur between nonpolar molecules (Van der Waals) Dipole-dipole forcesDipole-dipole forces occur between polar molecules Hydrogen bondingHydrogen bonding occurs between molecules with an H-F, H-O, or H-N bond Intermolecular forces determine phase!

4. weakest IMF = dispersion forces - occur between nonpolar molecules - occur between nonpolar molecules ● Monatomic molecules: He, Ne, Ar, Kr, etc. ● Diatomics of same element: O 2, H 2, N 2 ● Symmetric molecules: C 4 H 10 Dispersion forces ↑ as size molecule ↑

5. Dipole-dipole forces occur between: - polar molecules (permanent charge separation) HCl and HBr are examples of polar diatomic molecules

6. Hydrogen bonding occurs between molecules containing an H-F, H-O, or H-N bond H-bonding: strongest IMF H-bonding: strongest IMF

7. Properties of Covalent (Molecular) Substances Poor conductors of heat & electricity –no charged particles! Low mp & low bp –easy to pull molecules apart from each other Majority of solids are soft Low H f and H v compared to ionic & metallic substances High VP compared to ionic & metallic substances

8. mp, bp, H f and H v and vapor pressure depend on how hard it is to pull particles apart Weak IMF – easy to pull particles apart Strong IMF – more difficult to pull apart

9. Which substance has the strongest intermolecular forces? The weakest? Water Ether