4 states of matter: Liquids, Solids, Gases, and Plasma

Intermolecular forces (weakest to strongest):

The forces involved in the three states of matter (from weakest to strongest)

• Intermolecular forces
• Covalent bonding
• Ionic bonding
• Network covalent bonding

The change in phases is caused by the change of forces among the molecules.

London dispersion forces- forces between non-polar and noble gas molecules. The molecules involved have zero dipole moment. Generally, more electrons means greater Dispersion forces

Polarizability-as the atomic number of the atom increases, the # of electrons and protons also increases. This increase changes the momentary dipole action.

Based on this principle, as # of molecules or atom increases, the London dispersion forces also increase.Examples of molecules with London dispersion forces: CH₄ ; C₂H₄ ; He

*The London dispersion forces in C₂H₄ > CH₄ because ethane has more electrons.

Dipole-dipole attractions-forces between polar molecules. The positive pole of the molecule attracts the negative pole of another molecule. This force is only 1% as strong as a covalent or ionic bond. The strength of the force is inversely proportional to the distance between the two molecules.

Hydrogen Bonding-the strongest intermolecular force. Its strength is largely due to the small size of the hydrogen atom and the large polarity in the resulting molecule.

The atoms that form hydrogen bonding are the following: Fluorine (F), Nitrogen (N), and Oxygen (O).

Gas State:

For tutorial on gas click here.

Liquid State:

Basic properties of liquid

• Low compressibility
• High density compared to gas
• Lack of rigidity
• Viscosity-measure of resistance to flow (stronger intermolecular forces = greater viscosity)
• Surface tension-resistance of liquid to increase its surface area (stronger intermolecular forces = greater surface tension)
• Capillary action-the sudden rise in level of liquid in tight space

Cohesive forces-intermolecular forces between the molecules in the liquid

Adhesive forces-intermolecular forces between the liquid and the container

Water creeps up glass because…

1.Water and glass are polar
2. Molecules in glass orient themselves to attract the water molecules. (Dipole-dipole attractions)
3. Both water and glass have strong intermolecular forces so adhesive forces equals cohesive forces
4. Once they reach a balance, the result is a concave meniscus

For mercury, cohesive forces> adhesive forces because there is no attraction between mercury, nonpolar, with glass, polar. The result is a convex meniscus.

• Crystalline solids- organized structures of its components
• Amorphous solids- disorganized arrangement of its components
• Lattice- a 3-D representation of the components of the solid
• Unit cell- the smallest repeating unit of the lattice

Heat of fusion, D H_fus, is enthalpy change at the melting point of the solid.

Also known as vaporization. The energy to vaporize 1 mole of a liquid at 1 atm is the heat of vaporization, D H_vap.

When a liquid is sealed in a closed container, the liquid evaporates, but at the same time the gas condenses back to the liquid state. Equilibrium is reached when the rate of condensation equals the rate of evaporation. The equilibrium vapor pressure is also the vapor pressure of the liquid.

Heating Curve for water:

A Sample Phase Diagram

Triple point-the temperature and pressure in which all 3 states of matter co-exist in equilibrium

Critical point-the endpoint of the liquid-gas line where no matter how much the pressure and temperature are varied, the gas will not liquefy.

*The slope of the solid-liquid line is negative if the liquid state is denser than the solid states.