NGSS · Middle School (6–8)
Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed.
Clarification statement: Emphasis is on qualitative molecular-level models of solids, liquids, and gases to show that adding or removing thermal energy increases or decreases kinetic energy of the particles until a change of state occurs. Examples of models could include drawing and diagrams. Examples of particles could include molecules or inert atoms. Examples of pure substances could include water, carbon dioxide, and helium.
Why water teaches this standard well
Water is the clarification's first named pure substance, and its familiar freezing, melting, and boiling make it the model case for particle motion and state change. The same phase changes are the engine of the water cycle, linking this chemistry standard back to Earth science.
Materials tagged with this code are written to the full standard , including its clarification statement , and each carries a written note explaining the alignment. See how we review materials.
Grade 6 Lesson plan
A 50-minute grade 6 lesson where students model evaporation and condensation to explain how a solar still turns seawater into fresh water in a fictional coastal town.
Grade 7 Worksheet
A grade 7 worksheet using a reservoir through the seasons to model how heat changes particle motion during freezing, melting, and evaporation in the water cycle.
Grade 7 Lab / experiment
A grade 7 science lab where students build a solar still that evaporates and condenses salt water, measure the fresh water collected, and calculate percent yield.
Grade 6 Writing prompt
A grade 6 science argument prompt: students use a fictional winter temperature profile to explain why a pond freezes from the top down and stays liquid below.
Grade 6 Writing prompt
A grade 6 science argument prompt using a fictional town's break log, frost depths, and repair notes to explain why water main breaks peak in late winter.