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 The Phases of Matter How do the mass, volume, and densities of solid, liquid, and gas compare?

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.

As heat energy is added to ice, the temperature increases until it reaches 0°C. Then the temperature stops increasing. As you add more heat, more ice becomes liquid water but the temperature stays the same. This is because the added energy is being used to break the intermolecular forces and change solid into liquid. Once all the ice has become liquid, the temperature starts to rise again if more energy is added.

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?