An attractive intermolecular force resulting from the tendency of polar molecules to align themselves such that the positive end of one molecule is near the negative end of another. Diplole- Dipole Van der Waals forces The weak attractive forces between molecules or atoms resulting from the small, instantaneous dipoles that occur because of the varying positions of the electrons about the nuclei of atoms. London Dispersion Forces A weak to moderate attractive force that exists between hydrogen atoms covalently bonded to very electronegative atoms, particularly F, O, or N and the lone pair of electrons of another electronegative atom in another molecule Hydrogen Bonding

P4O10, Cl2, AgCl, I2 Br2, Ne, HCl, N2 Ar, Kr, Xe, Ne Circle the one with the lowest boiling point. P4O10, Cl2, AgCl, I2 Circle the one with the highest intermolecular bond strength Br2, Ne, HCl, N2 Circle the one with the highest boiling point. Ar, Kr, Xe, Ne Rank boiling points 1-5 (with 5 being the highest) BaCl2, H2, CO, HF, Ne 5 1 3 4 2 HF, HCl, HBr, HI Rank bond strengths 1-4 (with 4 being the highest) 4 1 2 3

Net force inward on the surface particles! (Evidence of attractive forces at work!) Surface Tension: A resistance in liquids to create new surfaces …due to an imbalance of forces on particles on the surfaces of liquids

energy used to overcome attractive forces DHv Heating Curve for a Typical Liquid energy used to overcome attractive forces DHv Heat of vaporization Temperature → B.P. L→ G L clusters→ random Time