History of The Atomic Model

Many lessons on atomic structure begin with a recitation of the historic developments that led to the current theory. It is a valuable experience for students to understand that scientific ideas evolve over time in response to new and better data. Using a timeline layout, students will illustrate major atomic developments and outline how ideas changed over time. They should be sure to include a variety of different scientists and discoveries related to atomic theory in their timeline.

Students can upload pictures of these scientists or, in some cases, of their equipment, using Photos for Class. They can also describe the major advancements in each description box to make as detailed or general a timeline as is required by the level of chemistry they are studying.

For an alternative to the timeline layout, have students create a timeline poster to incorporate into a presentation or gallery walk. You can add more than one template to this assignment to give students lots of options!

Suggested Scientists

• Democritus is often credited with the first atomic theory, though it was a philosophical idea without evidence. He is also credited with using the word "atomos" to describe a small unit of matter that was unbreakable.
• John Dalton completed scientific experiments to develop his atomic model with evidence. His theory included the ideas that atoms make up all matter, are indivisible, and that atoms of an element are identical.
• JJ Thomson is credited with proving the first part of Dalton’s theory incorrect when he discovered the electron, as a result of his cathode ray tube experiment.
• Ernest Rutherford later showed that most of the mass and all of the positive charge of an atom is found in a small dense core of the atom that we call the nucleus.
• Niels Bohr suggested that electrons move on orbits like planets around a sun. This was later found to be too specific a model and was pushed aside for the current theory of quantum mechanics which is based on mathematics and describes a probability of “locating” an electron.