of data; precision is critical to supporting evidence-derived explanations of the behavior of matter. Students should be expected to apply their understanding of matter in the context of earth and life sciences, recognizing that matter conservation, energy conservation, and matter flows are critical concepts for understanding many large-scale phenomena.
Using evidence collected and analyzed from their own investigations, evidence from outside sources (e.g., atomic images), and the results of simulations, students confirm a model that matter consists of atoms in motion—with forces between the atoms—and that the motion of the particles is temperature dependent. Students can connect this particle model of matter to observations and present arguments based on it to defend the following claims: All substances are made from approximately 100 different types of atoms, which combine with one another in various ways; atoms form molecules that range in size from two to thousands of atoms; gases and liquids are made of molecules or inert atoms, which are moving about relative to each other; and in a solid, atoms may vibrate in position but do not change relative locations.
Students can select different materials as examples to support the claim that solids may be formed from molecules or may be extended structures with repeating subunits (e.g., crystals, metals). Recognizing that pure substances are made from a single type of atom or molecule, students present evidence to support the claim that each pure substance has characteristic physical and chemical properties that can be used to identify it.
Boundary Statement. In this grade band, the forces and structures within atoms and their role in the forces between atoms are not introduced—nor are the periodic table and the variety of types of chemical bonds.