Grades 9-12: Endpoint and Progression

By the end of grade 12. Each atom has a charged substructure consisting of a nucleus, which is made of protons and neutrons, surrounded by electrons. The periodic table orders elements horizontally by the number of protons in the atom’s nucleus and places those with similar chemical properties in columns. The repeating patterns of this table reflect patterns of outer electron states. The structure and interactions of matter at the bulk scale are determined by electrical forces within and between atoms. Stable forms of matter are those in which the electric and magnetic field energy is minimized. A stable molecule has less energy, by an amount known as the binding energy, than the same set of atoms separated; one must provide at least this energy in order to take the molecule apart.

At this grade band, the structures within atoms and their relationships to the forces between atoms are introduced. Students’ understanding of the particle model of matter is developed and refined through investigations and analysis of data, both their own and those from experiments that cannot be undertaken in the science classroom. Increased sophistication, both of their model-based explanations and the argumentation by which evidence and explanation are linked, is developed through mathematical and language skills appropriate to the grade level.

Students’ conceptual models of matter are extended, based on evidence from their own and others’ investigations, to include the following: atoms have a charged substructure of a nucleus (made from protons and neutrons) surrounded by electrons; the periodic table orders elements by the number of protons and places those with similar chemical properties in the same columns; and the repeating patterns of this table reflect patterns of outer electron states. Students can cite evidence that supports this model and relate it to the properties of matter, particularly to the variety of elements, isotopes, and chemical properties.

Students use their understanding of electrical interactions to support claims that the structure and interactions of matter at the bulk scale (link to PS2.A) are determined by electrical forces within and between atoms. Students also use their understanding of stability within systems (link to PS2.B) and the relationship between forces and energy (link to PS3.C) to support claims that stable forms of matter are those that minimize the energy in electric and magnetic fields within the system. Students can then argue that this model is consistent with the propositions that a stable molecule has less energy (by an amount known as the binding energy, which is the sum of all bond energies) than the same set of atoms separated and



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