HS-PS1-7: Conservation of Atoms in Chemical Reactions

Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction. (Energy and Matter)

Clarification Statement: Emphasis is on using mathematical ideas to communicate the proportional relationships between masses of atoms in the reactants and the products, and the translation of these relationships to the macroscopic scale using the mole as the conversion from the atomic to the macroscopic scale. Emphasis is on assessing studentsโ€™ use of mathematical thinking and not on memorization and rote application of problem-solving techniques

Assessment Boundary: Assessment does not include complex chemical reactions.

Disciplinary Core Ideas
PS1.B: Chemical Reactions

Crosscutting Concepts
Energy and Matter


The following assessments were created by science teachers hoping to better understand the NGSS. In most cases teachers went from standard to assessment in around an hour.  These are drafts and should be used accordingly. Feel free to improve these assessments or contribute to the collection. Learn more about assessment design here.




Chemical reaction
Balanced chemical equation
Reactants and products
Atoms (or molecules or ions)
Conservation of mass
Atomic scale
Macroscopic scale


Lesson Plans


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