• 6-8: 4D/M1a. All matter is made up of atoms, which are far too small to see directly through a microscope.
• 9-12: 4D/H1. Atoms are made of a positively charged nucleus surrounded by negatively charged electrons. The nucleus is a tiny fraction of the volume of an atom but makes up almost all of its mass. The nucleus is composed of protons and neutrons which have roughly the same mass but differ in that protons are positively charged while neutrons have no electric charge.
• 9-12: 4D/H2. The number of protons in the nucleus determines what an atom's electron configuration can be and so defines the element. An atom's electron configuration, particularly the outermost electrons, determines how the atom can interact with other atoms. Atoms form bonds to other atoms by transferring or sharing electrons.

• 9-12: 10F/H1. In the late 1700s and early 1800s, the idea of atoms reemerged in response to questions about the structure of matter, the nature of fire, and the basis of chemical phenomena.
• 9-12: 10F/H3. In the early 1800s, British chemist and physicist John Dalton united the concepts of atoms and elements. He proposed two ideas that laid the groundwork for modern chemistry: first, that elements are formed from small, indivisible particles called atoms, which are identical for a given element but different from any other element; and second, that chemical compounds are formed from atoms by combining a definite number of each type of atom to form one molecule of the compound.
• 9-12: 10F/H4. Dalton figured out how the relative weights of the atoms could be determined experimentally. His idea that every substance had a unique atomic composition provided an explanation for why substances were made up of elements in specific proportions.

This classroom-tested learning module gives a condensed, easily-understood view of the development of atomic theory from the late 19th through early 20th century. The key idea was the discovery that the atom is not an "indivisible" particle, but consists of smaller constituents: the proton, neutron, and electron. It discusses the contributions of John Dalton, J.J. Thomson, Ernest Rutherford, and James Chadwick, whose experiments revolutionized the world view of atomic structure.

• Physical Sciences K-8 History and Discovery Unit
• Physics First History and Discovery Unit
• Conceptual Physics History and Discovery Unit
• Algebra-Based Physics History and Discovery Unit