Skip to main content Skip to main content

Essential Science for Teachers: Physical Science

The Particle Nature of Matter: Solids, Liquids, and Gases Children’s Ideas About Solids, Liquids, and Gases

Below are common ideas children in grades K-6 have about this topic, compiled from research on children’s ideas about science. Consider what evidence might refute this idea, and why a child would be likely to believe this? Once you’ve entered all your answers you can click “printable page” at the bottom of this form to print your answers. You can also click “see possible response” for any question to see one possible response from the series content advisors.

1. Matter is continuous and static.

Children’s everyday experience does not include the microscopic world of particles, and solids/liquids do not appear to move when at rest. However, many macroscopic behaviors, like the fact that gases can be compressed or that solids expand when heated, would not be possible if matter were continuous. In the former case, the amount, or mass, of gas would have to decrease (impossible, because matter can never be created or destroyed) and, in the latter case, the solid would have to gain mass (again, impossible). The evidence that matter is not static can be seen in the Brownian Motion of particles that can be observed under a microscope, as demonstrated in the video with a mixture of oil and water.

2. Most gases contain air and are weightless, invisible, and/or are poisonous.

Children are often confused about the nature of gases, because many gases they encounter every day are invisible — like air — and are very light. They may have also had experience with a gas stove or heater, which are dangerous when unlit, or heard about poisonous gases from the media. However, what we call air is actually a mixture of gases, e.g. nitrogen, oxygen, and carbon dioxide, all of which have weight. Many gases, like helium and hydrogen, are pure, i.e., contain no air or other gases, and some like iodine have color. Many gases aren’t poisonous and, perhaps most importantly, any substance can change state to a gas if its liquid form is heated to its boiling point.

3. Particles of a solid have all or most of the bulk solid’s properties, including hardness, hotness/coldness, color, and physical state.

Most children don’t have a grasp of the difference in scale between the macroscopic world and the microscopic world. All material can exist in any state, so hardness and other properties are only characteristics of one state, not of the particles that make it up.

Series Directory

Essential Science for Teachers: Physical Science


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