• 6-8: 4D/M1a. All matter is made up of atoms, which are far too small to see directly through a microscope.
• 6-8: 4D/M3ab. Atoms and molecules are perpetually in motion. Increased temperature means greater average energy of motion, so most substances expand when heated.
• 6-8: 4D/M3cd. In solids, the atoms or molecules are closely locked in position and can only vibrate. In liquids, they have higher energy, are more loosely connected, and can slide past one another; some molecules may get enough energy to escape into a gas. In gases, the atoms or molecules have still more energy and are free of one another except during occasional collisions.
• 6-8: 4D/M8. Most substances can exist as a solid, liquid, or gas depending on temperature.
• 6-8: 4D/M10. A substance has characteristic properties such as density, a boiling point, and solubility, all of which are independent of the amount of the substance and can be used to identify it.

• 6-8: 11B/M1. Models are often used to think about processes that happen too slowly, too quickly, or on too small a scale to observe directly. They are also used for processes that are too vast, too complex, or too dangerous to study.
• 6-8: 11B/M6. A model can sometimes be used to get ideas about how the thing being modeled actually works, but there is no guarantee that these ideas are correct if they are based on the model alone.

Students in the middle grades often have trouble understanding why the measured volume increases slightly when water is heated. Many have the misconception that volume is always conserved in a physical change (they confuse mass and volume). This multimedia resource provides a clear way to understand the volume differences that can occur when molecules move further apart or closer together by heating/cooling. Includes assessment with answer key.

• Physical Sciences K-8 Matter and Interactions Unit
• Physics First Matter and Interactions Unit

This excellent resource covers three difficult concepts in one multimedia package: 1) Substances change phase because of changes in the motion of their atoms or molecules, 2) Heating a substance increases molecular motion while cooling decreases it, and 3) Volume increases slightly when water is heated (in other words, volume is not always conserved in a physical change, though mass IS conserved.) Includes two interactive simulations and a hands-on lab.

• Physical Sciences K-8 Teaching about Heat and Thermal Energy Unit
• Physics First Teaching about Heat and Thermal Energy Unit