Skip to main content Skip to main content

Essential Science for Teachers: Physical Science

The Particle Nature of Matter: Solids, Liquids, and Gases

What simple idea links together all of chemistry and physics? How can a close study of the macroscopic differences among solids, liquids, and gases support a microscopic model of tiny, discrete, and constantly moving particles? In this session, participants learn how the "particle model" can be turned into a powerful tool for generating predictions about the behavior of matter under a wide range of conditions.

Learning Goals

During this session, you will have an opportunity to build understandings to help you:

A liquid (water).

  • Recognize characteristics of a good scientific model
  • Understand the macroscopic evidence for each of the four basic principles of the particle model of matter:

    1. Matter is made of tiny particles.
    2. There is empty space between the particles.
    3. The particles are in constant motion.
    4. There are forces that act between the particles


Video Overview

What explanation might account for the differences between the states of matter, as well as explain its different properties? Session 2 introduces the particle model of matter, the principles which underlie a wide range of phenomena. By contrasting this model with what is variously called the continuous, continuum, or plenum model, this session shows how the particle model is useful for making accurate predictions about a variety of behaviors of matter on a macroscopic scale.

Video Outline

The video begins by defining what scientists mean by the term “model,” establishing what makes a good model, and describing the process by which models are continually revised. Then, children in the Science Studio divide a piece of aluminum foil into the smallest pieces possible and are asked: Is it possible to go on dividing forever? Is there ever a point at which the pieces no longer have the properties of the aluminum foil? Science historian Dr. Al Martinez recounts the history of the continuous model originally proposed by the Greeks, explains its appeal, and later tries to use this model to explain the expandability and compressibility of gases.

Back in the Science Studio, children continue to reveal their models of matter, which support what science education research says about the difficulty children sometimes have connecting their ideas about macroscopic matter with the particles that make it up. By “taking a trip into a drop of water,” we then explore the size and scale that make this connection so challenging. This raises the question, “What’s in between the particles of matter?”

For an answer, we first explore fifth graders’ ideas on the subject, and then visit vacuum engineer Bob Childs, whose work in nuclear fusion relies on an important principle of the particle model. We return to the Science Studio one last time, where we find children further developing their models to explain the compressibility of gases and proposing a model to explain an everyday change of state—boiling.

In Session 2’s Featured Classroom segments, Linsey Newton’s third graders in Hudson, Massachusetts, observe two more changes of state—evaporation and condensation—and Russell Springer’s fifth graders in Newtonville, Massachusetts, try to explain the seemingly random movement of oil droplets suspended in water. In both classrooms the students express a variety of macroscopic rationale for what is happening.

Series Directory

Essential Science for Teachers: Physical Science


Produced by Harvard-Smithsonian Center for Astrophysics. 2004.
  • Closed Captioning
  • ISBN: 1-57680-749-5

Related Materials