Phases of Matter

Chapter 10

Phases of Matter: are determined by the energy content and

movement of the particles

What keeps the particles in liquids and solids together?

The movement of particles is directly related to the temperature of the substance,as the temperature cools the movement of the molecules slows and the moleculesmaybe attracted to each other.

This is referred to as INTERMOLECULAR FORCES. Intermolecular forces are theattraction between molecules. These attractions are weaker than intramolecular forces like ionic and covalent bonds.

The intermolecular forces can determine many of the physical properties of the substance. The stronger the intermolecular forces the higher the melting and boiling points of the substance. Why do you think this might be?

Why?

The stronger the intermolecular forces the higher the energy required to disturb or break the attractions.

Types of intermolecular forces:Dispersion Forces (Van der Waals):Temporary attraction created as electrons orbitthe nucleus.

(-) (-)

Positive nuclei will repel each other.

+ +

Types of intermolecular forces:Dispersion Forces (Van der Waals):Temporary attraction created as electrons orbitthe nucleus.

(-) + (-) +

When the electrons are concentrated on the same side as an exposed positive nuclei there will be an attraction. Creating a temporary bond between the two atoms.

Types of intermolecular forces:Dispersion Forces (Van der Waals):Temporary attraction created as electrons orbitthe nucleus. (weak attraction)

Dipole – Dipole:The attraction between the oppositely charged ends of polar molecules.

N

H

H

H

δ+ δ- N

H

H

H

δ+ δ-

(-) + (-) +

Hydrogen Bonding:The attraction created when a hydrogen atom is bonded to a highly Elecronegative atom (F, O, N). This attraction causes a higher thanexpected boiling point. (strong attraction)

H

HO

H

HO

How do substances change state?

Beginning State Ending State Process of Change

Solid Liquid Melting

Solid Gas Subliming

Liquid Solid Freezing

Liquid Gas Evaporating/Boiling

Gas

Gas

Solid

Liquid Condensing

Deposition

Boiling Points• The temperature at which a substance turns from liquid to vapor

• Thought question:

Is the boiling point of a liquid the same in every location?

Boiling point is directly related to atmospheric pressure, and indirectly related to altitude!

Location Altitude (ft) Pressure Boiling Point

Sea Level 0 760 mmHg 100 ºC (373 K)

Mt. Everest 29,028 240 mmHg 70 ºC (343 K)

Boiling vs. Evaporation

Occurs below the boiling point, only at the surface of the liquid.

Occurs at the boiling point, throughout the entire liquid.

Heat of vaporization: the amount of heat required to vaporize a liquid.

Normal Boiling Point: the temperature at which vapor pressure of a liquid is equal to atmospheric pressure.

Freezing and Melting PointsAt what temperature does water freeze?

At what temperature does ice melt?

(Freezing point)

(Melting point)

Heat of Fusion: the amount of heat required to melt a solid to liquid

We often use graphs to show the correlation between vapor pressure and boiling. The graph below is the vapor pressure curve for four different substances. Using this graph we can find the “Normal boiling point” for any substance by observing its boiling point at

standard pressure (101.3 kPa, 1 atm, 760 mmHg).

For example the “normal boiling point” of substance A would be 35°C. What would the normal boiling of substance D be?

100°C Based on this information, what do you think substance D might be?

Line D represents water. If the atmospheric pressure in a flask is lowered to 70 kPa, water would boil at what temperature?

Line D represents water. If the atmospheric pressure in a flask is lowered to 70 kPa, water would boil at what temperature?

Do the practice graph in your packet.

• Answers:

• 1. ~32kPa, ~7kPa (your answer may differ by +/- 1)

• 2. 70ºC

• 3. ~21kPa

• 4. ~74ºC, ~115ºC

Particles are Always in Motion

GASES1. Gases are composed of tiny particles

2. Particles are in constant motion

3. Elastic collisions occur between particles

4. There are no attractive forces between particles

5. Kinetic Energy increases when temperature increases.

Particles are Always in Motion

LIQUIDS1. Viscosity: the friction or resistance to motion that exists

between the molecules of a liquid

2. Surface Tension: the imbalance of forces at the surface of a liquid

Particles are Always in Motion

SOLIDS1. Particles are “locked” in position and can only vibrate

2. Can be classified by three main characteristics:

• Hardness

• Electrical Conductivity

• Melting Point

How do we classify solids?Crystalline Solids:

• organized, repetitive unit cells, sharp melting point

• metallic: conduct electricity well

• molecular: soft, low melting point

• ionic: hard, brittle

• covalent-network: conduct electricity at high temperatures

Amorphous Solids:

• not “true” solids because molecules do move some

• high viscosities make them appear solid

• they soften before melting

For Next Class:

• Complete homework page of packet.