All matter is made up of atoms, which are far too small to see directly through a microscope.
Learning Goal 1cd
Atoms may link together in well-defined molecules, or may be packed together in crystal patterns. Different arrangements of atoms into groups compose all substances and determine the characteristic properties of substances.
Learning Goal 3ab
Atoms and molecules are perpetually in motion. Increased temperature means greater average energy of motion, so most substances expand when heated.
Learning Goal 8
Most substances can exist as a solid, liquid, or gas depending on temperature
For Grades: 9-12
Learning Goal 7a
Atoms often join with one another in various combinations in distinct molecules or in repeating three-dimensional crystal patterns.
Learning Goal 10
The physical properties of compounds reflect the nature of the interactions among its molecules. These interactions are determined by the structure of the molecule, including the constituent atoms and the distances and angles between them.
For Grades: 6-8
Learning Goal 3
Thermal energy is transferred through a material by the collisions of atoms within the material. Over time, the thermal energy tends to spread out through a material and from one material to another if they are in contact. Thermal energy can also be transferred by means of currents in air, water, or other fluids. In addition, some thermal energy in all materials is transformed into light energy and radiated into the environment by electromagnetic waves; that light energy can be transformed back into thermal energy when the electromagnetic waves strike another material. As a result, a material tends to cool down unless some other form of energy is converted to thermal energy in the material.