1. States of Matter (Ch. 5) Notes

2. Atoms and molecules in liquids and gases
A fluid is a form of matter that flows when any force is applied, no matter how small
Liquids and gases are fluids
Molecules in a liquid can flow and change shape, but has constant volume
Molecules in a gas can also flow, but can expand to fill a container
In general, liquid is less dense than the same material in solid form (not water)

3. Pressure
If pressure is applied to a bowling ball is is just transmitted downward because a bowling ball is a solid
Pressure applied to a balloon acts in all directions
In a fluid pressure is a distributed force per unit area that acts within a fluid
On a microscopic level pressure comes from collisions between atoms

4. Intermolecular Force
Intermolecular forces between separate atoms and molecules are attractive at a distance, but repulsive at close range
Intermolecular forces always try to bring molecules close (but not overlapping)
Thermal energy causes molecules to vibrate and spread apart
When molecules have a lot of thermal energy (high temperature), intermolecular forces are completely overcome and the molecules spread apart, as in a gas
Medium amount of thermal energy – liquid
Low amount of thermal energy- solid

5. Melting and boiling
Melting point is the temperature at which a substance changes from a solid to a liquid
H2O = 0C; Fe = 1500C
Boiling point is the temperature at which a substance changes from a liquid to a gas
H2O = 100C; Fe = 2862C
It takes energy to overcome intermolecular forces

6. Evaporation and condensation
Evaporation is the change from liquid to gas at a temperature below the boiling point
Evaporation takes energy away from a liquid because the molecules that escape are the ones with the most energy (sweat)
Condensation is the change from gas to liquid at a temperature below the boiling point
Molecules with less than the average energy stick to a cool surface forming drops of liquid
Condensation raises the temperature of a gas because the lower- energy, liquid condenses leaving the higher-energy atoms in the gas.

7. Convection
Convection is the transfer of heat through the motion of fluids such as air and water
Natural convection- hot water/air circulates to the top and cooler water/air sinks to the bottom creating a circulating flow
Forced convection- creating the above circulating flow with pumps (boiler v. radiator)

8. The molecular structure of solids
Solids have a definite shape and constant volume
Physical properties of solids:
Density: mass per unit volume
Strength: the ability to maintain shape under great force
Elasticity: the ability to stretch and return to the same shape
Ductility: the ability to bend without breaking
Brittleness: the tendency to crack or break; opposite of elasticity
Thermal conductivity: the ability to transmit heat energy
Electrical conductivity: the ability to allow electricity to flow

9. Crystalline solids
Crystalline solids have an orderly, repeating pattern of molecules or atoms
Most naturally occurring solids on Earth are crystalline
Salt
Steel
Silicon

10. Polymers
Amorphous solids do not have a repeating pattern of molecules or atoms
Rubber
Glass
Wax
Polymers are materials in which individual molecules are made of long chains of repeating patterns
Plastic- ex: Polyethylene
Useful because they melting points well above room temperature but much lower than most metals

11. Heat conductors in solids
Heat conduction is the transfer of heat by the direct contact of particles of matter
Molecules of hotter materials (cocoa) lose energy and molecules of cooler materials (spoon) gain energy
Eventually both materials are the same temperature…
Thermal equilibrium is a condition where temperatures are the same and no heat flows

12. Thermal conductors and insulators
Although conduction occurs in liquids and gases, solids make the best conductors because the molecules in a solid are packed close together.
Air is a poor conductor which is why a down jacket keeps you warm.
Materials that conduct heat easily are called thermal conductors (metals)
In general, good electrical conductors are also good thermal conductors
Materials that conduct heat poorly are called thermal insulators (foam, plastic, wood)
Heat conduction cannot occur through a vacuum (thermos)

13. Summary
Write a 4-7 sentence summary with highlighted/underlined academic vocabulary focusing on how liquids solids and gases are alike and different.