Solids, Liquids, and Gases Notes

I. How do solids and liquids differ from gases? Solids – intermolecular forces are sufficiently strong relative to kinetic energy – molecules are virtually locked in place often in a very orderly pattern (crystalline structures) – definite volume and shape

Liquids Liquids – attractive intermolecular forces between molecules is comparable to kinetic energies of molecules – molecules are held in close proximity, but still move in a rather chaotic motion – definite volume but no definite shape – considered a fluid

Gases Gases – molecules/particl es in chaotic motion – average kinetic energy is greater than the attractive forces between molecules – have no definite volume or shape – considered a fluid

II. Intermolecular Forces (IM) - These are weak forces that exist between molecules and are responsible for the fact that the substance can exist as a liquid (and/or solid). Molecules of gases have little to no intermolecular forces (which is why gases have no definite shape or volume). Dipole-dipole IM forces, London dispersion, and hydrogen bonding are intermolecular forces.

IntrAmolecular Forces are the bonds or forces within the atoms of a molecule; the two bonds connecting two hydrogen atoms to an atom of oxygen in water are intrAmolecular forces. The force holding water molecules together so they don’t evaporate are intErmolecular forces and are about l/6 to l/l0th as strong as single covalent bonds. Covalent, ionic, and metallic bonding are intramolecular forces. Metallic bonding is the strongest of the three.

Intramolecular Force Draw this picture in your notes!

Dipole – Dipole Forces

Hydrogen Bonding

Practice Problems – True or False: 1. Gases have a definite volume. True or False? 2. Solids are considered fluids. True or False? 3. Dipole-dipole, London dispersion, and hydrogen bonding are intermolecular forces. True or false? 4. Intermolecular forces describe the forces of attraction between one molecule and another molecule. True or false? 5. Intramolecular forces describe the bonds between atoms within a molecule. True or false? 6. Gases have little to no intermolecular forces so they have no definite shape or volume. True or false? 7. Covalent, ionic, and metallic bonding are the three intramolecular forces. True or False? 8. Ionic bonds are the strongest of the three intramolecular forces. True or False?

III. Phase Changes 1. vaporization (+  H); liquid to gas 2. condensation (-  H); gas  liquid 3. sublimation (+  H); solid  gas 4. deposition (-  H); gas  solid 5. melting (+  H); solid  liquid 6. freezing (-  H); liquid  solid Phase changes involve the breaking and forming of intermolecular forces.

The phase changes that involve the breaking of intermolecular forces of attraction include melting, vaporization, and sublimation melting, vaporization, and sublimation These require an input of energy to overcome the attractive forces between the particles of the substance.

The phase changes that involve the forming of intermolecular forces of attraction include freezing, condensation, and deposition These release energy as the particles adopt a lower-energy conformation.

The strength of the intermolecular attractions between molecules, and therefore the amount of energy required to overcome these attractive forces (as well as the amount of energy released when the attractions are formed) depends on the molecular properties of the substance. Generally, the more polar a molecule is, the stronger the attractive forces between molecules are.

Phase Diagrams: a graph of pressure VS temperature that shows the conditions under which the phases of a substance exist. Phase Diagram for Water

Phase Diagram for Carbon Dioxide