Chapter 12 Chem 115

Liquid

• molecules have ~equal energy and intermolecular forces

• molecules are closely packed in random orientation

Gas 

molecules are located far apart and have freedom of motion 

molecules have more kinetic energy and weaker intermolecular forces 

Solid

molecules are closely packed in fixed positions

molecules have less kinetic energy and stronger inermolecular forces

Ice→ water vapor

sublimation

vapor → ice 

deposition 

Endothermic phase changes

• melting

• evaporation

• sumblimation

Exothermic phase changes

• deposition

• freezing

• condensation

intermolecular forces

forces between two molecules 

• london dispersion

• dipole- dipole

• hydrogen bonding

• ion-dipole

intramolecular forces

forces within a molecule

• ionic and covalent

London dispersion

• Instantaneous dipole that occurs accidentally in an atom induces a similar dipole in a neighboring atom.

• between all molecules

• non-polar

• covalent

• significant in larger molecules/atoms

Dipole-dipole 

• between polar molecules 

Hydrogen bonding

• occurs between hydrogen: Nitrogen, Oxygen, or Fluorine

• Strong dipole-dipole forces

As IMFs increase:

• viscosity, boiling point, and surface tension:

  • increase

• vapor pressure

  • decreases

Surface Tension

resistance of a liquid to an increase in its surface area
Liquids with large intermolecular forces tend to have high surface tensions.

Capillary action

0. spontaneous rising of a liquid in a narrow tube:

   Cohesive forces – intermolecular forces among the molecules of the liquid.
   Adhesive forces – forces between the liquid molecules and their container.
   

0. Vapor Pressure

0. is the partial pressure of its vapor in dynamic equilibrium with its liquid (rates of condensation and evaporation are the same).
   Vapor pressure increases with increasing T, decreasing strength of IMF, independent of surface area (equal impact on evaporation and condensation)

∆Hvap

is amount of heat required to vaporize 1 mol of liquid at 1 atm

For vaporization, ∆Hvap is and for condensation, ∆Hvap is

positive

negative

The rate of vaporization increases with:

• Increasing surface area increasing temperature decreasing strength of IMF

volatile

Liquids that evaporate easily

• those that do not vaporize easily are nonvolatile.

Metallic solids

Discrete molecules held together by intermolecular forces 

• see of collectively share electrons (covalent bonds)

• wide range of hardness and melting points

• conductor 

• iron, silver, brass 

Ionic solids

Extended network of ions held together by cation-anion interactions

• ionic bonds 

• hard 

• high melting point 

• unsulator 

• sodium chloride 

• calcium fluoride 

Molecular solids

discrete molecules held together by weak forces '

• Polar: dipole-dipole

• Non polar: london dispersion

• soft

• low melting point

• insulator

• fire extinguisher

• ice and dry ice

Covalent-network solids

Joined by extensives network of covalent bonds

hard 

high melting point 

insulator 

diamond