States of Matter (Ch. 5) Notes

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)

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

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

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

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.

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)

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

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

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

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

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)

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