Properties of Matter

• Chapter Four: Density and Buoyancy

• Chapter Five: States of Matter

Scientific Models Must:

• 1. Address a question about something from the real world

• 2. Include entities (sometimes invisible and/or hypothetical) and rules for how they interact.

• 3. Be consistent with the evidence that we have, and make predictions about future observations

• 4. Be revisable• 5. Be public

Tanker Video

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 not bound 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 ofcommon substances

• Materials have a wide range of melting and boiling points.

5.1 Melting and boiling points ofcommon 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 fromskin 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 watervapor 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?