Liquids Properties of liquids are similar to solids’, and way different from gas properties density compressibilities enthalpy changes attractive forces

INTERMOLECULAR ATTRACTIVE FORCES between molecules (liquids & solids) Forces that act between molecules (or atoms) keeping them in one phase, liquid A sample of a liquid will remain in that phase until IAFs are overcome, usually due to an increase in temperature or pressure For IAFs, you focus on many molecules in a sample, once you have determined if you have polar or non-polar bonds between the atoms that make up the molecules Remember, bond determination occurs due to electronegativity differences between two atoms (0.0 – 0.4 – non-polar covalent bond, 0.4 – 1.9 polar covalent bond, > 1.9 – ionic bonds) IAF determination occurs when you look at the interaction of molecules.

TYPES of IAFs 1.dipole-dipole Occurs between 2 polar molecules Polar molecules have a partial negative end (pole) δ+ δ- H-----F F is more negative, therefore hogs (  ) the electrons in the bond Many H---F molecules attracted to each other A strong force The molecules hold onto each other, won’t allow them to escape to gas phase (evaporate, boil)

2. Hydrogen Bonding A force between molecules NOT a bond between atoms A special type of dipole-dipole Between H and N, O, or F The STRONGEST IAF!!! Molecules with hydrogen bonding have the highest melting and boiling point of covalent, molecular compounds --- why? δ+Hδ+H δ-Oδ-O δ+Hδ+H Each H—O bond is polar Eneg difference is 1.4 Oxygen is the hog 

3. Ion-dipole forces Between ion and greatly polar molecule, like Accounts for solubility Ionics in H 2 0 – solutions Na—Cl soluble? Yes, why? -Cl ion is attracted to δ+ H in H Na ion is attracted to δ- O in H 2 0 If the attraction is strong enough, the compound will be soluble. Is PbSO 4 soluble?

4. London dispersion forces Also called van der Waals forces Among non-polar molecules Weakest IAF Minimal attraction H 2, Cl 2, CO 2 at room temperature are gases, overcome IAFs