Toward an Accessible Set of Chemistry Core Ideas to Help Students Make Sense of Phenomena

organizing core ideas

I attended a professional development session on  by Brett Moulding and Nicole Paulson based on the book they wrote with Rodger Bybee, . My key takeaway from the training is that the cornerstone of the NGSS approach is student explanations of the causes of phenomena they have investigated, accompanied with arguments supported by evidence that aims to convince others why the explanation should be accepted. The purpose of the NGSS is to provide a structure for students to successfully do this. The structure that is promoted by the NGSS to help students achieve this outcome consists of the three dimensions: science and engineering practices, crosscutting concepts, and disciplinary core ideas. The scope of this post is limited to the crosscutting concepts and core ideas.

According to the presenters of the professional development I attended, the crosscutting concepts and core ideas are intended to be used as evidence to support explanations and arguments. I have been thinking that it would be helpful for my students (and for me) to have a succinct and understandable list of the core ideas that apply to Chemistry. I have found several lists of Chemistry core ideas online, but I don’t think I would give the ones I have seen to my students because they are either too long or written with language that I don’t think is suitable for novice learners of Chemistry.



I have compiled a list of the crosscutting concepts and 12 core ideas for high school Chemistry that my students could use to support the explanations and arguments I will be asking them to write. My goal is for this list to be succinctly written in language that will be accessible/understandable to high school students, yet still be acceptably thorough. My working definition of a core idea is an important idea that is broad enough to be used to help explain or support a wide variety of phenomena and that helps to facilitate making connections across topics of study. I have compiled my list of core ideas from the 1, 2, the Journal of Chemical Education article, 3(available without a JCE subscription), 4 by Atkins that was published in Chemistry Education in New Zealand, and my own reflection. The purpose of this post is to elicit comments, feedback and suggestions from the ChemEd X community so my list can be refined and simplified as much as possible.

Because “crosscutting concepts” are core ideas that can be used to explain ANY phenomenon, regardless of the field of science the phenomenon might be associated with, they are included in this list of core ideas for Chemistry.

Crosscutting Concepts   

Help to Explain Any Phenomenon from All Fields of Science


  • A system is the matter you are choosing to look at during an investigation. Everything else is the surroundings. The universe consists of the system and its surroundings.
  • The matter in a system is made of atoms that have mass, occupy space, and are arranged in specific patterns.
  • Scale, quantities, and proportions help to define your system.


  • Patterns are things you notice that repeat. They can be used as evidence for an argument, to make predictions, or to classify things.
  • All systems go through periods of stability and change. Some systems change quickly while others change slowly. Some systems go through repetitive cycles of change. Equilibrium represents a condition of stability where factors of a system balance each other out.


  • Cause and effect tells how and why something happens. It forms the premise of an explanation.
  • Matter cycles. It can change appearance and form, but never appears from nowhere or disappears into nothing. The total number of each type of atom remains constant after a physical or chemical change.
  • Energy flows. It is transferred when any kind of change happens and is often seen as movement, sound, light, or temperature changes. Energy flows when heating, working, or radiating takes place. Energy can be stored and converted between various forms as it flows, but it tends to become more spread out in the universe as it moves. Energy never appears from nowhere or disappears into nothing because the total amount of energy in the universe doesn’t change.
  • The shape, arrangement, and structure of a sample of matter determine its properties and ability to perform certain tasks or functions.
  • Forces are a push or pull from interactions that occur between different pieces of matter. Most common phenomena can be connected to electromagnetic forces and/or gravitational forces.
    • Note: I know that Forces are not mentioned as a crosscutting concept, but I think that forces should be mentioned under cause and effect.


Core Ideas for Chemistry 

Considered in Addition to the Crosscutting Concepts

Composition of Matter

  • Each atom has a positively charged nucleus, which is made of protons and neutrons, surrounded by negatively charged electrons that move around the nucleus in discrete energy levels.
  • Every substance has a unique set of properties that can be used to describe and identify it.
  • Atoms of different elements show patterns and trends in their properties, which reflect patterns in the structures of their atoms.
  • Particles of matter are always in motion; their speed is directly related to temperature.

Attractions in Matter

  • Electromagnetic forces cause attractions and repulsions in matter. The varying strength of these forces results in the different properties we see across matter.
  • Any bond or attraction is paired with the exchange of a specific amount of energy. The quantity of energy that is required to break a bond or attraction is also the quantity of energy that was released when the bond or attraction originally formed.
  • Bonds form between atoms by the transfer or sharing of electrons so the atoms involved can reach a stable energy condition of having a complete outer electron level.

Changes in Matter

  • Some bonds between atoms are broken and new ones formed during chemical change, which causes atoms to be rearranged and recombined in different ways to form new substances.
  • Atoms retain their identity after chemical change.
  • Chemical change occurs when collisions between particles of matter overcome energy barriers.
  • Energy flow during changes is a balance between the energy required to break bonds and other forces of attraction and the energy released when new bonds and attractions are formed. When a change is exothermic, the newly formed bonds or attractions release more energy than was required to break the original bonds or attractions. The opposite is true of endothermic changes.
  • A change in matter will only occur if energy becomes more spread out in the universe as a result of the change

My hope is that together these concepts and ideas can be used to help write explanations and arguments for all phenomena a high school Chemistry student will encounter.

What do you think? Is this list of concepts and ideas potentially helpful in the NGSS-driven quest to describe phenomena? Does this short list accurately distill the vast topic of Chemistry? Do you see a way to further simplify any part of this? Are there any modifications you would make? Any errors to fix? Please leave your comments below.


Editors' Note: Dustin Williams published another NGSS post, "".


  1. DCI Arrangements of the NGSS, (accessed 3/28/18)
  2. College Board AP Chemistry Course and Exam Description, (accessed 3/28/18)
  3. Core Ideas and Topics: Building Up or Drilling Down?, Melanie M. Cooper, Lynmarie A. Posey, and Sonia M. Underwood, Journal of Chemical Education 2017 94 (5), 541-548. (accessed 3/28/18)
  4. Chemistry’s Core Ideas, Peter Atkins, Chemistry Education in New Zealand, August, 2010. (accessed 3/28/18)