By the end of this unit students will be able to:

- Describe how the following people contributed to the atomic theory: Democritus, Dalton, Thomson, Rutherford, Lavoisier, and Proust.
- Compare and contrast the Law of Definite Proportions and the Law of Multiple Proportions and understand how they helped Dalton to derive the first atomic theory.
- Know the main points of Dalton’s Atomic Theory and how they have been updated.
- Know the basic idea of Rutherford’s Gold Foil experiment and the two things it proved.
- Compare and contrast each model of the atom with its immediate predecessor.
- Know the following about the three basic subatomic particles: location in the atom, relative mass, charge, who discovered it, and order of the discovery.
- Tell the number of protons, neutrons, and electrons in an atom given either mass number notation or nuclear notation.
- Define cation and anion and solve for the number of protons, neutrons, and electrons.
- Identify a set of elements as being isotopes or different elements.
- Solve for the average atomic mass of a set of isotopes.
- Use the mole to convert between liters, grams, and atoms.
- Describe how the following people contributed to the atomic theory: Democritus, Dalton, Thomson, Rutherford, Lavoisier, and Proust.
- Compare and contrast the Law of Definite Proportions and the Law of Multiple Proportions and understand how they helped Dalton to derive the first atomic theory.

Explore Isotopes and Atomic Mass at PhET