Intramolecular Bonds the bond within the molecule that holds the atoms together
Intermolecular Forces forces between molecules
Types of Intermolecular Forces
1. Van der Waals Forces
- Weak attractive forces caused by the movement of electrons within a molecule
- Randomly moving electrons may at one point be nearer to one atom than another
- Temporary dipole formed
- If two molecules with opoositely charged temporary dipoles are near each other an attractive force will exist E.g. H(-)H(+) — H(-)H(+)
- Sometimes a temporary dipole in one molecule will induce a dipole in another
- Results in greater boiling point
- Greater number of electrons = greater number of temporary dipoles = greater boiling point
- Occurs in non-polar and polar molecules
2. Dipole – Dipole Interactions
- Negative end of one dipole is attracted to the positive end of another
- Permanent forces (due to polarity)
- Stronger than van der Waals forces, weaker than hydrogen bonding
- Results in greater boiling point
- Occurs in polar molecules
3. Hydrogen Bonding
- Occurs when hydrogen is bonded to highly electronegative atoms (O, N, F)
- Strong – Requires more energy to break than regular covalent bonds – Higher boiling point
- Oxygen (-) has an attraction to neighbouring hydrogen (+) molecules, and vice versa
- Covalent bond > Hydrogen bond > Dipole-dipole interactions > van der Waals forces
- H2S should have a higher boiling point (greater molecular mass) but the H-S bond is much less polar than the O-H bond
- Hydrogen bonding only occurs between hydrogen and small atoms (O, N, F) because the charge is much more concentrated and therefore, more effective
