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Liquids

Liquids. Properties of liquids are similar to solids’, and way different from gas properties density compressibilities enthalpy changes a ttractive forces . Intermolecular Attractive Forces between molecules (liquids & solids).

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Liquids

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

  2. 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.

  3. TYPES of IAFs • 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)

  4. 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- O Each H—O bond is polar Eneg difference is 1.4 Oxygen is the hog  δ+ H δ+ H

  5. 3. Ion-dipole forces • Between ion and greatly polar molecule, like • Accounts for solubility • Ionics in H20 – solutions • Na—Cl soluble? Yes, why? • Cl ion is attracted to δ+ H in H20 + Na ion is attracted to δ- O in H20 • If the attraction is strong enough, the compound will be soluble. Is PbSO4 soluble?

  6. 4. London dispersion forces • Also called van der Waals forces • Among non-polar molecules • Weakest IAF • Minimal attraction • H2, Cl2, CO2 at room temperature are gases, overcome IAFs

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