Unit 2: Atomic Structure and Nuclear Chemistry

This unit builds toward the following NGSS performance Expectations (PE’s). Links to evidence statements are provided:

• HS-PS1-8:  Develop models to illustrate the changes in the composition of the nucleus of the atom and the energy released during the processes of fission, fusion, and radioactive decay. [Clarification Statement: Emphasis is on simple qualitative models, such as pictures or diagrams, and on the scale of energy released in nuclear processes relative to other kinds of transformations.] [Assessment Boundary: Assessment does not include quantitative calculation of energy released. Assessment is limited to alpha, beta, and gamma radioactive decays.]

• HS-ESS1-1: Develop a model based on evidence to illustrate the life span of the sun and the role of nuclear fusion in the sun’s core to release energy in the form of radiation. [Clarification Statement: Emphasis is on the energy transfer mechanisms that allow energy from nuclear fusion in the sun’s core to reach Earth. Examples of evidence for the model include observations of the masses and lifetimes of other stars, as well as the ways that the sun’s radiation varies due to sudden solar flares (“space weather”), the 11-year sunspot cycle, and non-cyclic variations over centuries.] [Assessment Boundary: Assessment does not include details of the atomic and sub-atomic processes involved with the sun’s nuclear fusion.]

• HS-ESS1-3: Communicate scientific ideas about the way stars, over their life cycle, produce elements. [Clarification Statement: Emphasis is on the way nucleosynthesis, and therefore the different elements created, varies as a function of the mass of a star and the stage of its lifetime.] [Assessment Boundary: Details of the many different nucleosynthesis pathways for stars of differing masses are not assessed.]

• HS-ESS1-6: Apply scientific reasoning and evidence from ancient Earth materials, meteorites, and other planetary surfaces to construct an account of Earth’s formation and early history. [Clarification Statement: Emphasis is on using available evidence within the solar system to reconstruct the early history of Earth, which formed along with the rest of the solar system 4.6 billion years ago. Examples of evidence include the absolute ages of ancient materials (obtained by radiometric dating of meteorites, moon rocks, and Earth’s oldest minerals), the sizes and compositions of solar system objects, and the impact cratering record of planetary surfaces.]

Appendix E

This unit focuses on these Disciplinary Core Ideas

• PS1.C Nuclear Processes

  • Nuclear processes, including fusion, fission, and radioactive decays of unstable nuclei, involve release or absorption of energy. The total number of neutrons plus protons does not change in any nuclear process.

  • Spontaneous radioactive decays follow a characteristic exponential decay law. Nuclear lifetimes allow radiometric dating to be used to determine the ages of rocks and other materials. (secondary)

• PS3.D: Energy in Chemical Processes and Everyday Life

  • Nuclear fusion processes in the center of the sun release the energy that ultimately reaches Earth as radiation. (secondary)

• ESS1.A: The Universe and Its Stars

  • The star called the sun is changing and will burn out over a lifespan of approximately 10 billion years.

  • The study of stars’ light spectra and brightness is used to identify compositional elements of stars, their movements, and their distances from Earth.  

  • Other than the hydrogen and helium formed at the time of the Big Bang, nuclear fusion within stars produces all atomic nuclei lighter than and including iron, and the process releases electromagnetic energy. Heavier elements are produced when certain massive stars achieve a supernova stage and explode

• ESS1.C: The History of Planet Earth

  • Although active geologic processes, such as plate tectonics and erosion, have destroyed or altered most of the very early rock record on Earth, other objects in the solar system, such as lunar rocks, asteroids, and meteorites, have changed little over billions of years. Studying these objects can provide information about Earth’s formation and early history.

Appendix F

This unit focuses on these Science and Engineering Practices 

• Constructing Explanations and Designing Solutions. Constructing explanations and designing solutions in 9–12 builds on K–8 experiences and progresses to explanations and designs that are supported by multiple and independent student-generated sources of evidence consistent with scientific ideas, principles, and theories.  

  • Apply scientific reasoning to link evidence to the claims to assess the extent to which the reasoning and data support the explanation or conclusion.

• Developing and Using Models. Modeling in 9–12 builds on K–8 and progresses to using, synthesizing, and developing models to predict and show relationships among variables between systems and their components in the natural and designed worlds. 

  • Develop a model based on evidence to illustrate the relationships between systems or between components of a system.

• Obtaining, Evaluating, and Communicating Information.  Obtaining, evaluating, and communicating information in 9–12 builds on K–8 experiences and progresses to evaluating the validity and reliability of the claims, methods, and designs.  

  • Communicate scientific ideas (e.g., about phenomena and/or the process of development and the design and performance of a proposed process or system) in multiple formats (including orally, graphically, textually, and mathematically).

Appendix G

This unit contains these Crosscutting Concepts

• Stability and Change

  • Much of science deals with constructing explanations of how things change and how they remain stable.

• Energy and Matter  

  • In nuclear processes, atoms are not conserved, but the total number of protons plus neutrons is conserved.

• Scale, Proportion, and Quantity  

  • The significance of a phenomenon is dependent on the scale, proportion, and quantity at which it occurs.

This unit focuses on these Connections to the Nature of Science

• Science Models, Laws, Mechanisms, and Theories Explain Natural Phenomena

  • A scientific theory is a substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment, and the science community validates each theory before it is accepted. If new evidence is discovered that the theory does not accommodate, the theory is generally modified in light of this new evidence.  

  • Models, mechanisms, and explanations collectively serve as tools in the development of a scientific theory.