1.5 class periods

3-1 Phases of Matter

The purpose of this section is to introduce students to the phases of matter and to describe the movement of particles in each of the four phases. Students will learn that on Earth matter exists in solid, liquid, and gaseous phases, and they will investigate the movement of particles in each phase. They will also learn of another phase of matter called plasma that exists in stars. The main thrust of the section, however, is to note the differences among the phases that occur naturally on Earth. When studying the gaseous phase, students will be introduced to Boyles and Charless laws and will use them to predict the effects of temperature and pressure on the volume of a gas.

The themes that can be focused on in this section are energy, patterns of change, and scale and structure. All these themes, as they relate to phases of matter, are interconnected by the commonality of the structure and motion of particles in each phase.

Energy: Tell students that the amount of energy that the particles of a substance possess determines the phase of the substance. Particles in a solid have less energy than the particles of a liquid. Particles of a gas have more energy than the particles of a liquid.

Patterns of change: Point out that matter can exist in four phases: solid, liquid, gas, and plasma. Although the physical properties of a substance change as it passes through the various phases, the particles themselves do not change. The substance remains the same substance. No new substances are produced.

Scale and structure: Stress that the properties of solids, liquids, and gases are related to the arrangement of particles that make up the substance. You may wish to point out that the particles in a solid are so tightly packed that they are only able to vibrate. In a liquid, they can slide over one another, and in a gas they are spread even farther apart.

Performance Objectives 3-1

1. Identify a phase as an important physical property of matter.
2. Describe the four phases of matter.
3. State the gas laws.

Science Terms 3-1

Physical property, p.62

Phase, p.62

Solid, p.62

Crystal, p.63

Liquid, p.64

Gas, p.65

Plasma, p.68

• What kind of matter is ice?
• How is ice different from water?
• How is the ice the same as water?
• What is the other phase of water?

Have students observe Figure 3-2, p.62.

• What is the shape of the sodium chloride crystals?
• How many flat surfaces are on each cube?
• How many chlorine spheres surround each sodium sphere within the cube?
• How many sodium spheres surround each chlorine sphere?

Fill a breaker or cylindrical container with water. As students watch, pour the water into a rectangular container.

• How do you know that a substance is a liquid?
• Could I pour water into any size container? Why not?
• Would water fit any shape container provided it was large enough?
• Predict how the particles of a liquid are arranged.
• If I had used motor oil instead of water, would the results have been the same or different?

Show students an air-filled balloon.

• What is inside this balloon?
• What phase of matter is air?
• What shape is the air?
• What is the volume of the air?

Let the air out of the balloon.

• What is the shape of the air now?
• What does this tell you about the particles of a gas?

Write on the chalkboard:

Volume up Þ , pressure down à .

Volume down à , pressure up Þ .

Point out that this relationship between volume and pressure is called Boyles law. Explain that Boyles law states that the volume of a fixed amount of gas varies inversely with the pressure exerted on it, provided the temperature remains constant.

Then tell students that when pressure is held constant, the volume of a gas increases as temperature increases and decreases as temperature decreases. This is Charless law. Stress that this temperature-volume relationship assumes that the pressure remains constant.

Have students determine which of the following statements represent an inverse relationship and which represent a direct relationship:

The greater the number of hours worked, the more money earned. (direct)

The greater a cars speed, the farther it travels in one hour. (direct)

The more hours you sleep in a day, the fewer hours you are awake. (inverse)

The greater the number of cars on the road, the greater the chances of an accident. (direct)

The more people who enter a contest, the less chance you have of winning. (inverse)

• What are the four phases of matter?
• How is a crystalline solid different from an amorphous solid?
• Using the gas laws, predict what will happen to the volume of a gas if (a) the pressure triples, (b) the temperature is halved, (c) the pressure is decreased by a factor of five, (d) the pressure is halved and the temperature is doubled.