Key Idea: When substances interact to form new substances, the atoms that make up the molecules of the original substances rearrange into new molecules.

Students are expected to know that:

  1. During a chemical reaction the atoms that are linked together in molecules (or arranged in other patterns such as arrays and crystals) rearrange to make new molecules.
  2. If the atoms are not rearranged, then a chemical reaction has not occurred.
  3. New substances are made of the same kinds of atoms as the original substances (i.e., the atoms themselves did not change during the reaction).


  1. The idea that the number of each kind of atom stays the same will be assessed under Idea H (conservation of matter).
  2. Students are not expected to know the term “bond” or how chemical bonds are formed or broken during chemical reactions.
  3. They are not expected to know that during chemical reactions, atoms are not turned into energy.