Classification of Matter
How Are the Four States of Matter Described?
Teacher Note: Connections
Students will begin to observe patterns of particle type and arrangement in matter at different scales and cite patterns as empirical evidence for
causality in supporting their explanations of classifying matter as they explore this concept. Help students begin to make this connection by passing out handouts containing sketches of particles that represent pure substances and mixtures. See the types of sketches used in the final assessment item, “Classifying Matter,” at the end of this Explore for examples. Do not label the sketches, but ask students to describe the differences between the sketches. These can be collected following this initial activity and brought out again at the end of the lesson for students to evaluate by applying the knowledge that they have gained throughout the lesson. By the end of this lesson, students should be able to recognize the patterns of molecular makeup that correspond to the various types of matter including pure substances, solutions, heterogeneous mixtures, homogeneous mixtures, alloys, suspensions, and colloids.
As students read and comprehend complex texts, view the videos, and complete the interactives, labs, and other Hands-On Activities, have them summarize and obtain scientific and technical information. Students will use this evidence to support their initial ideas on how to answer the Explain Question or their own question they generated during Engage. Have students record their evidence using “My Notebook.”
The Four States of Matter
Matter exists in four states. Each is characterized by its physical properties. The four states of matter are solids, liquids, gases, and plasmas.
Solids are materials that have a definite shape and a definite volume. An example would be an ice cube. An ice cube is a six-sided object whose volume can be determined by multiplying its height, depth, and width. The particles in an ice cube, which are molecules of water (H2O), are densely packed and vibrate in fixed positions. Solids are almost incompressible, which means they resist being packed together more tightly.
Liquids are materials that have an indefinite shape and a definite volume. We say that liquids have an indefinite shape because they take the shape of the container they occupy. However, their volume is definite. They do not expand to fill the container they occupy. For example,
liquidglossary term (opens in a new window) water in a graduated cylinder will take the shape of the cylinder. The water has a definite volume, which can be determined by reading the cylinder’s scale. The water will fill only a certain space in the cylinder. In other words, 50 mL of water in a 100 mL cylinder will not expand to fill the cylinder. The volume will remain 50 mL, no matter what the container looks like. The particles in liquid water are relatively loosely arranged, and are somewhat free to move past one another. Liquids are almost incompressible. Like solids, they resist being packed together more tightly.
Gases are materials that have an indefinite shape and an indefinite volume. Water vapor, which is a
gasglossary term (opens in a new window), will take the shape and volume of the container in which it is enclosed. This means that the volume of a sample of water vapor will vary with the volume of its container. For example, water vapor contained in a 1 L bottle will have a volume of 1 L. The same mass of water vapor contained in a 2 L bottle will have a volume of 2 L. The particles of a
gasglossary term (opens in a new window) are widely separated and are very free to move from one place to another. Gases are compressible.
Physical Properties of Solids, Liquids, and Gases
How might cooling affect the properties of the states of matter?
Each of these states of matter can be transformed into another state of matter by adding or subtracting energy. This is commonly accomplished by adding or subtracting
heat energyglossary term (opens in a new window), i.e., heating and cooling the matter. For example, heat transforms a
solidglossary term (opens in a new window) ice cube to a liquid, and then a gas. Cooling a gas, such as water vapor, transforms the gas to a liquid, and then to a solid.
Plasmaglossary term (opens in a new window) is the fourth state of matter.
Plasmaglossary term (opens in a new window) is similar to a gas in some ways, but particles in the plasma state have much greater kinetic energy. When atoms or molecules absorb extremely high amounts of energy, they break apart into ions (charged particles) and free electrons. The electric charges of these ions and electrons affect the properties of plasma. Usually the energy absorbed when gas changes to plasma is in the form of heat and involves temperatures greater than 5000°C.
Conditions on Earth’s surface do not naturally sustain matter in the plasma state. While plasma does exist in Earth’s atmosphere for short periods of time, it is unstable. Plasma on Earth quickly releases energy and returns to the gas state. Examples include static electricity (which we see as lightning) and the auroras.
Plasma is found in outer space. The atmospheres of stars, for example, are made of plasma. Also, in the space between stars, tiny amounts of matter exist, often in the plasma state.
Scientists on Earth can produce plasma under certain conditions and use them in everyday products. Plasma TVs, welding machines, fluorescent lights, and neon signs are some examples. More complex devices use plasma in the investigation of nuclear energy, especially energy produced by fusion reactions. A fusion reaction occurs when the nuclei of two atoms combine. Fusion reactions produce the energy in stars. If harnessed, fusion might become an unlimited source of energy for humankind.
Because of its extremely high energy, plasma often is confined by magnetic fields that attract and repel the charged particles, keeping it in place.
Teacher Note: Connections
Students describe changes of energy and matter in the system of states of matter as they work through this item, Phase Diagram Analysis. They should be able to apply what they have learned about how energy input is required to cause state changes, and relate that to the increasing temperature along the x-axis of a phase diagram. They may need help relating the increase in pressure along the y-axis to changes in state, and so you may wish to have a class discussion before administering this item to have students work through the effects of pressure on matter.
In this discussion, begin with a sketch of particles in the gas phase, and ask students how an increase in pressure is likely to affect the state of the sample. Then, ask them to describe how a decrease in pressure could affect the state of a solid or liquid sample. Another pre-assessment note that you likely will want to pass along to students is to make them aware that the two terms “state” and “phase” are used interchangeably in this context.
