The boiling point of a substance is a measure of the amount of energy needed to:

increase the speed of the molecules in the liquid phase to that of their gas phase

(The heavier it is, the higher the boiling point)

overcome any intermolecular forces (“molecular stickiness”)

Consider the following polar molecules:

Substance Boiling Point (C)Molar Mass Dipole moment

HF 2020 1.83

H2O 10018 1.80

HCl -8536 1.08

H2S -6034 0.97

SO2 -1064 1.61

The polarity of a molecule is more important in determining boiling point than its mass.

Water’s unusual properties are due to its:

Surface tension: uneven distribution of the intermolecular dipole-dipole interactions increases the strength of the intermolecular hydrogen bonding at the surface

Adhesive properties: the small size and high polarity of water causes it to adhere (wet) other polar substances

Cohesive properties: a large molecular dipole moment causes water to stick to itself

Non-polar polyesterPolar spider silk (a polypeptide)

How much will dissolve?

Saturated solution: No more solute will dissolve.

Unsaturated solution: Haven’t added enough solute to the solvent for the solution to be saturated. If more solute is added, it will dissolve.

Supersaturated solution: Have ‘tricked’ the solution so that there is more solute dissolved in the solvent than is present in a saturated solution. Adding more solute causes the excess solute to precipitate out of solution.

Solubility curves

Plots the MAXIMUM

number of grams of a

solute that will dissolve

in 100 g of the solvent

at particular

temperatures.

2. Is a solution containing 80 g of NH4Cl at 80o C saturated, unsaturated or supersaturated?

1. Is NaNO3 or KNO3 more soluble at 50o C?

4. Is a solution containing 80 g of KNO3 at 80o C saturated, unsaturated or supersaturated?

Ce2(SO4)3

3. What is least soluble at 40oC?

5. At what temp. will crystals appear for the solution in #4?

50oC

The three common states of matter are:

Definite volumeDefinite shape

Definite volumeIndefinite shape

Indefinite volumeIndefinite shape

Three basic assumptions:

1. All matter is composed of small particles (atoms, molecules, ions). The amount of space (volume) that the particles take up depends upon the distance between the particles and not on the size of the particles themselves.

2. These particles are in constant random motion.

3. The particles undergo elastic collisions (no loss of energy) with each other and the walls of their container.

Absolute zero: The temperature at which ALL molecular motion stops. (0 K = -273°C = -460°F)

Solids: The particles in solids can be arranged in three different ways.

1. In a regular repeating pattern that extends over long distances.

A glassy material:Short-range order only

A crystalline material:Has long-range order

2. With a pattern that only repeats over short distances.

3. Amorphous solids have no long or short range order.

Charcoal:Amorphous carbon

Graphitic carbon:‘glassy’ carbon

Diamond:Crystalline carbon

Allotropes: different structural forms of the same element

Intermolecular Forces: Whether a substance is a liquid, solid or gas depends upon the strength of the intermolecular forces holding it together.

OOHH

OOHHLet’s get

to stickin’!!

Let’s get to

stickin’!!

Indefinite shape and volumeCompressible

Flows readily/rapid diffusion

Indefinite shape, definite volumeVirtually incompressible

Flows readily/slow diffusion

Definite shape and volumeVirtually incompressible

Does not flowDiffusion is very slow

Gas Liquid

Solid

Intermolecular Forces: the properties of materials (solubility, viscosity, boiling point, freezing point, heat capacity*) depend upon the strength of the interactions BETWEEN the particles.

There are six types of intermolecular forces:

1. Ion-ion

2. Ion-dipole

3. H-bonding

4. Dipole-dipole

5. Dipole-induced dipole

6. Induced dipole-induced dipole (also called London Dispersion Forces, or LDF)

STRONGEST

weakest

1. Ion-ion: exists between oppositely charged ions (atoms that have gained or lost electrons and are no longer electrically neutral). The strength of this interaction increases as the magnitude of the charge increases.

<<Na+1 Cl-1 Mg+2 O-2

NaCl is soluble in water, MgO is not.

2. Ion-dipole: exists between ions and polar molecules (e.g. water, alcohols)

3. H-bonding: Is a special case of dipole-dipole interaction because it is significantly stronger. It occurs whenever H is

bonded to either N, O or F.

C F

H

H

H

CH

H

H

OH

C

H

H

H

OH

+

-

No intermolecularH-bonding possible

H-bonding between H on OH and O on next OH

4. Dipole-dipole: interaction between molecules with permanent dipoles that do not have H-bonding

5. Dipole-induced dipole: The permanent dipole of a polar molecule causes a distortion of the electron cloud around a nonpolar molecule and INDUCES A TEMPORARY DIPOLE.

HCN+ -

C6H14

6. Induced dipole-induced dipole: A temporary redistribution of the electron cloud around a NONPOLAR molecule induces a temporary dipole in an adjacent NONPOLAR molecule.

C6H14C6H14