H2O (s)

H2O ()

H2O (g)

The state (or phase) of matter is determined by the arrangement and motion of particles.

The motion of particles is governed by the kinetic energy (KE) of the particles (Remember that KE = 1/2mv2)

Solids Liquids Gases

Increase KE Increase KE

vaporization boiling

melting

Changes of State

condensation freezing

sublimation

deposition

sublimation

Intermolecular Forces: Attractive forces between molecules

Types of inter-molecular forces

1. dipole-dipole (1% as strong as covalent bonds)

A special type of dipole-dipole force is the hydrogen bond. These bonds form between molecules that contain a hydrogen atoms bonded to a very electronegative element like N, O or F. Hydrogen bonds are very strong compared to an ordinary dipole-dipole bond.

E.g HF, NH3, H2O all form hydrogen bonds

Hydrogen bonding 10% as strong as covalent bonds

Water molecules are polar molecules. The - oxygen forms intermolecular bonds with the + hydrogen of another water molecules. This is an example of a special type of intermolecular bond called a hydrogen bond.

Inter-molecular forces

2. London dispersion forces (instantaneous and induced dipoles) NON-POLAR MOLECULES

Non-polar molecule

Movement of electrons causes an instantaneous dipole

This induces a dipole in a nearby molecule

This instantaneous dipole will effect any nearby molecules

As we consider the properties of liquids (and solids) that KE and intermolecular attractions are governing the behavior of the substance

Vaporization: Change from liquid to gas via boiling process

Evaporation: Change from liquid to gas at the surface of a liquid, not caused by boiling

--This happens because the molecules at the top a of the liquid don’t have as strong of an attraction to the other molecules. (If they have high enough KE, they can escape)

Open Containers: Evaporation causes liquid molecules to leave as gases and escape (amount of liquid decreases)

Closed Containers:Evaporation causes liquid molecules to vaporize, but they get caught in the container, creating : VAPOR PRESSURE

In a sealed container, molecules will start to evaporate and the liquid’s volume will decrease.

But, after the air above the liquid becomes “saturated”, some of these molecules will then condense. After a short time, the volume of the liquid will not change.

This is known as Dynamic Equilibrium because the rates of evaporation and condensation are EQUAL .

Evaporation and Condensation DO NOT stop happening once the flask has reached equilibrium

The rate of evaporation = the rate of condensation

Boiling: When all the molecules of a liquid have enough kinetic energy to vaporize, the liquid is said to be boiling.

Boiling Point (bp): The temperature at which the vapor pressure of a liquid is just equal to the external pressure on the liquid.

Normal Boiling Point: The temperature at which a substance boils at atmospheric pressure (101.3kPa)

When water is heated, the kinetic energy of the molecules increases and eventually bubbles of vapor form within it. The vapor pressure in the bubble is the same as the vapor pressure of the water at that temperature.

When the temperature of the water reaches a point that the vapor pressure of the bubble equals atmospheric pressure, the bubbles get larger, rise to the surface, and escape as steam. The water begins to boil.

REMEMBER:

vapor pressure of the bubble equals atmospheric pressure

The water begins to boilatmospheric

pressure

450 mm Hg

450 mm HgAt lower atmospheric pressures, the kinetic energy does not have to be as high to make the vapor pressure in the bubble equal to atmospheric pressure.

58o C

By reducing the atmospheric pressure, The water begins to boil at a lower temperature.

2. Why do some liquids exhibit capillary action?

3. Why are some liquids more viscous than others?

1. Why, when you pour a liquid onto a surface does it form droplets?

Hg H2O

Viscosity: is the resistance to motion of a liquid.

Maple syrup is more viscous than water. But water is much more viscous than gasoline or alcohol.

The stronger the attraction between molecules of a liquid, the greater its resistance to flow and so the more viscous it is.

Consider the following substances

a) molasses b) water c) ethyl alcohol

1. Which is the least viscous?

2. Which substance has the strongest intermolecular attractions?

Ethyl alcohol

Molasses

The inward force or pull which tends to minimize the surface area of any liquid is surface tension.

This water strider uses surface tension to his advantage

Surface tension in water is caused by hydrogen bonding between polar molecules. The more polar a liquid the stronger its surface tension.

The smallest surface area a liquid can form is a sphere.

Hg pure H2O H2O with detergent

Surface tension occurs because the molecules on the surface of the liquid cannot bond to the outside molecules. As a result, they look for something else to bond to (in order to increase stability). They get “pulled” in towards each other until their surface area is minimized, thus minimizing the contact with the outside.

**Surfactants are compounds that reduce the surface tension of a liquid (soaps and detergents are examples)**

Capillary action is the spontaneous rising of a liquid in a narrow tube.

Two forces are responsible for this action:

Cohesive forces: the intermolecular forces between molecules of the liquid

Adhesive forces: the attractive forces between the liquid molecules and their container

Hg H2O

If the container is made of a substance that has polar bonds then a polar liquid will be attracted to the container.

This is why water forms a concave meniscus while mercury forms convex meniscus

Solids generally have an orderly arrangement of atoms

Melting: When the kinetic energy of all the atoms in a solid is increased to a point where the atoms are able to freely flow around one another, the solid is said to have melted

Melting Point (mp): The temperature at which a solid turns into a liquid.

Crystalline

-Most solids are crystalline

-Contain particles arranged in an orderly, repeating, 3-D pattern called a crystal lattice

Non-Crystalline

- Amorphous solids have no set crystal structure

Examples:

1. Glass

2. Asphalt

3. Rubber

4. Plastic

5. Candles (Wax)

Some crystalline solids (pure substances) occur in a variety of different forms, known as Allotropes. Each allotrope has a different crystalline pattern that connects the atoms of the solid

Carbon, Sulfur, Phosphorus, Oxygen, Boron and Antimony all have allotropes

The most common examples of allotropes are found in elemental Carbon:

Diamond Graphite Buckminsterfullerene

(Bucky Balls)

Solids are almost always more dense than their liquid forms, however, there is one exception: ICE

Ice molecules are locked in fixed positions, held by intermolecular-bonds.

Ice is less dense than liquid water because the molecules are further apart than in liquid water.

vaporization boiling

melting

condensation freezing

sublimation

deposition

sublimation

boiling

Melting/Vaporization Curves: tracks temperature changes as a function of time and shows all state changes

boiling

Phase Diagrams: Shows the various conditions at which each state of a substance can occur