Section 1

• Kinetic Theory:• How particles in matter behave

• 3 Basic Assumptions of the Kinetic Theory1.All matter is composed of small particles (atoms,

molecules, and ions)

2.The particles are in constant, random motion

3.The particles are colliding with each other and the walls of their container

• Look at Figure 2 – Does the ice cube appear to be moving?

• Atoms in a solid are held tightly in place by the attraction between the particles.

• The attraction between the particles is what gives solids a definite shape and volume

• Thermal Energy:• Total energy of a material’s particles• Includes kinetic = vibrations and movement within and

between the particles• Also Potential = Forces that act within or between particles

• What does the thermal energy do to the particles in the solid cube?• Causes them to vibrate

• What happens if we lower the temperature of a substance?• Vibrate slower

• Molecules have kinetic energy at all temperatures – even absolute zero

• Which molecules move slower – molecules at 0 degrees C or 100 degrees C?

• Molecules at 0 degrees

• Temperature therefore relates to the average kinetic energy of particles in the substance or how fast the particles move

• Particles in a solid are closely packed together

• Have a geometric arrangement of particles

• Chemical and physical properties of a solid are attributed to the type of geometric arrangement

• Example:• Ice Cube

• What happens to a solid when thermal energy or heat is added to it?

• As the thermal energy is added the particles on the surface of the ice cube vibrate faster

• The particles on the surface transfer energy to other particles

• Eventually the particles have enough kinetic energy to overcome the attractive forces

• Melting point:• Temperature at which a solid begins to liquefy

• When the particles have enough kinetic energy to slip out of the ordered arrangement the ice melts

• Energy IS required for the particles to slip out of the ordered arrangement

• Heat of Fusion: • Amount of energy required to change a substance from

the solid phase to the liquid phase at its melting point

• Do particles have more kinetic energy as a solid or liquid?• Liquid

• What does the extra kinetic energy allow the particles to do?• Partially overcome the attractions to other particles• Allows particles to slide past each other• Allows liquids to flow• Allows liquids to take the shape of their container

• The attraction between particles is not quite overcome which is why liquids have a definite volume

• Do gas particles have enough kinetic energy to overcome the attraction between them?• Yes

• Gases do not have a fixed volume

• Fill the container they are in

• How does a liquid become a gas?• The particles in a liquid are constantly moving • Some have more kinetic energy than others• Particles moving fast enough can escape the attractive

forces

• When particles escape the attractive forces they can enter the gas state• This process is called vaporization

• 2 ways vaporization can occur?1. Evaporation

2. Boiling

• Evaporation• Vaporization that occurs at the surface of a liquid

• Can occur at temperatures below the liquids boiling point

• Have to have enough kinetic energy to escape the attractive forces of the liquid

• Boiling occurs at a specific temperature • Depends on the pressure on the surface of the liquid

• Boiling Point:• Temperature at which the pressure of the vapor in the liquid is

equal to the external pressure acting on the surface of the liquid

• External pressure = force pushing down on a liquid to keep the particles from escaping

• Heat of vaporization:• Energy required for the liquid at its boiling point to become a

gas

• Gas particles are moving quickly and are far apart

• Do not have a definite shape or volume

• Diffusion:• Particles spread throughout the “volume” until they are

evenly distributed

• Example:• Spraying air freshener in one half of the room

• Heating curve graph shows the temperature change of water as thermal energy is added

• What is going on when the temperature does not change?• All of the energy put into the ice is used to overcome the

attractive forces

• The temperature remains constant during melting

• After the attractive forces have been overcome then the temperature can increase

• The temperature remains constant again when water is boiling

• Plasma:• Matter consisting of positively and negatively charged

particles

• Is there an overall charge of the matter?• No, because there are equal numbers of the positively

and negatively charged particles

• How do we get plasma?• When particles undergo high energy conversions

electrons from the atom can get stripped off

• Plasma is found in lightning bolts and the Sun

• DISCUSS:• Seams in a concrete driveway

• Thermal Expansion:• Increase in the size of a substance when the temperature is

increased

• What happens when the temperature increases?• When temperature increases particles move faster and

separate

• When the particles separate the entire object expands

• What happens when the temperature decreases?• The particles move slower and the particles cannot over come

the attraction

• The particles move closer together and cause the object to shrink or contract

• Example:• Thermometer

• Addition of energy = particles moving faster

• Particles move apart

• Liquid in the thermometer expands / moves up the thermometer

• Example:• Hot-air balloons

• The air in the balloon is heated

• When the air is heated what happens?• Distance between particles increases

• The particles spread out causing the density of the hot air balloon to decrease

• Because the density is lower than the cooler air outside the balloon can rise

• There is always an exception to every rule

• Water molecules have a highly positive and negative areas• Figure 11

• The unlike charges are attracted to each other • Line up so that positive and negatives are near each other

• This causes empty spaces to occur

• Are the empty spaces bigger in a solid or liquid?• Solid

• So water expands when going from a liquid to a solid

• This causes solid ice to be less dense than water

• This is why ice floats on water

• Amorphous is Greek for “without form”

• Not all solids have a definite temperature at which they change from a solid to a liquid• Some soften and gradually change over a temperature

range

• These solids lack highly structured order

• Example:• Glass and Plastics

• Instead of a geometric arrangement they have a long chainlike structure

• Interactions between particles occur along the chain

• Some amorphous solids form when a liquid changes to a solid too quickly • An orderly structure does not have time to form

• Example: Obsidian – volcanic glass

• Liquid crystals DO NOT lose their ordered arrangement completely• Most substances lose their ordered arrangement as a

liquid

• Retain their geometric order in specific directions

• Highly responsive to temperature changes

• Use them to make LED watches, clocks, and calculators