Properties of Matter

• Chapter Four: Density and Buoyancy

• Chapter Five: States of Matter

Chapter Five: States of Matter

• 5.1 Liquids and Gases

• 5.2 Solid Matter

Investigation 5A

• How do the mass,

volume, and

densities of solid,

liquid, and gas

compare?

The Phases of Matter

5.1 Liquids and Gases

• A fluid is a form of matter that flows

when any force is applied.

• Gases and liquids are both called fluids.

5.1 Liquids and Gases

• In a liquid, molecules can slide over and

around each other.

• This is why liquids flow and can change

shape.

5.1 Liquids and Gases

• A gas is a phase of matter with high energy

molecules that can expand to fill a container.

• Molecules in a gas are free to move around and

so gases flow just like liquids.

Molecules in a gas have

much more energy than

molecules in a liquid.

5.1 Liquids and Gases

• Gases flow like

liquids, but they also

can expand or

contract to

completely fill any

container.

5.1 Pressure

• Forces in fluids are more complicated than forces in solids because fluids can change shape.

5.1 Pressure

• A force applied to a fluid creates

pressure.

• Pressure acts in all directions, not just

the direction of the applied force.

5.1 Pressure

• On the microscopic level, pressure comes from collisions between atoms.

• Every surface can experience a force from the constant impact of trillions of atoms.

• This force is what we measure as pressure.

5.1 Pressure

• The pressure inside

your tire is what

holds your car up.

5.1 Pressure

• There are two types of forces that act between atoms.

– The strongest forces are between atoms that are bonded together into molecules and compounds.

– A weaker type of force acts between molecules, or between atoms that are notbound together.

• We call these weak forces intermolecular forces.

5.1 Intermolecular Forces

• The phases of matter (solid, liquid, gas) exist

because of competition between thermal energy

and intermolecular forces.

– When molecules have a large amount of thermal

energy (high temperatures), intermolecular forces are

overcome and the molecules spread apart, as in a

gas.

5.1 Intermolecular Forces

– When molecules have a medium amount of

thermal energy, they come together to form a

liquid because the intermolecular forces are

partially overcome.

5.1 Intermolecular Forces

– When molecules have a small amount of

thermal energy, the intermolecular forces are

stronger and molecules become fixed in

place as a solid.

5.1 Melting and boiling

• The melting point is the temperature at

which a substance changes from a solid

to a liquid.

5.1 Melting and boiling

• The temperature at which a liquid becomes a gas is called the boiling point.

5.1 Melting and boiling points of

common substances

• Materials have a

wide range of

melting and

boiling points.

5.1 Melting and boiling points of

common substances

• Most materials have a higher density as a solid than as a liquid.

• Water is an exception.

• Ice wouldn’t float if ice were more dense than water!

• Ice helps fish and other aquatic organisms to survive over long, cold winters because the protective layer keeps the water below it warmer.

5.1 Evaporation and Condensation

• Evaporation occurs when molecules go from liquid to gas at temperatures below the boiling point.

• Evaporation takes energy away from a liquid because the molecules that escape are the ones with the most energy.

Sweat evaporating from

skin removes energy and

cools the body.

5.1 Evaporation and Condensation

• Condensation

occurs when

molecules go from

gas to liquid at

temperatures below

the boiling point.Dew forms when water

vapor in air condenses into

droplets.

5.1 Convection

• Convection is the transfer of

heat through the motion of

fluids such as air and water.

• Convection occurs because

fluids expand when they heat

up.

– Convection currents occur while

heating water.

– The hot water at the bottom of

the pot rises to the top and

replaces the cold water.

5.1 The atmosphere of Earth

• Air is the most important mixture of gases to

living things on the Earth.

• Air may seem like “nothing” but all the oxygen our

bodies need and all the carbon needed by plants

comes from air.

• Molecular nitrogen (N2) and oxygen (O2) together

account for 97.2 percent of the mass of air.

• Argon and water vapor make up most of the rest.

5.1 The atmosphere of Earth

• As a tree grows, you will

not see soil disappear to

provide mass for the tree.

• The oxygen and hydrogen

atoms in the tree come

from water.

• The carbon atoms come

from the carbon dioxide

(CO2) in the air.

5.1 The atmosphere of Earth

• Earth’s weather is created by gigantic

convection currents in the atmosphere.

5.1 The atmosphere of Earth

• Gravity creates pressure

because fluids have

mass and weight.

• The Earth’s atmosphere

has a pressure due to

the weight of air.

How does pressure change with

altitude in the atmosphere?