1.5 Compare the parts of the various atomic theories that stayed the same over time and those that changed.

(Atoms Exist) What idea about atoms have remained constant in atomic theories?

All models agree that matter is made of tiny, discrete particles called atoms.

(Atoms Exist) How has the understanding of atoms changed over time?

Originally thought to be indivisible (Dalton), later discovered to have subatomic particles (Thomson, Rutherford).

(Atoms Combine in Fixed Ratio) What did Dalton’s atomic theory say about chemical reactions?

Atoms combine in fixed ratios to form compounds, a concept that remained true in later models.

(Atoms Combine in Fixed Ratios) How did later models improve on Dalton’s idea of atoms combining?

Later models explained chemical bonding in more detail, incorporating charged particles (electrons, nucleus).

(Atoms Have Charge) Which scientist discovered electrons, proving atoms have charged components?

J.J. Thomson discovered electrons using cathode ray experiments.

(Atoms Have Charge) How did the understanding of atomic charge change over time?

Thomson’s model had electrons embedded in positive “pudding”; Rutherford’s model placed positive charge in a dense nucleus.

(Atoms Have a Nucleus) Which scientist discovered the nucleus, and how?

Rutherford discovered the nucleus through the gold foil experiment.

(Atoms Have a Nucleus) How did Rutherford’s model differ from Thomson’s?

Rutherford’s model placed the positive charge in a dense nucleus, unlike Thomson’s diffuse positive charge.

(Electron Arrangement) How did the idea of electron placement change over time?

Thomson thought electrons were scattered inside a positive atom; Rutherford proposed that electrons orbit a dense nucleus.