Which of Dalton's ideas about the atom was disproved by J.J. Thomson's cathode ray experiment?

• A. Atoms combine in simple whole-number ratios to form compounds.
• B. Atoms of the same element are identical in mass and properties.
• C. Atoms are indivisible and cannot be broken down into smaller particles.
• D. Atoms cannot be created or destroyed in chemical reactions.

Answer: (C)

Verified step by step guidance

1. Recall Dalton's atomic theory, which proposed several key ideas about atoms, including that atoms are indivisible and cannot be broken down into smaller particles.
2. Understand that J.J. Thomson's cathode ray experiment involved passing an electric current through a gas at low pressure, which produced rays (cathode rays) that were deflected by electric and magnetic fields.
3. Recognize that Thomson observed these rays were made of negatively charged particles (later called electrons), which are much smaller than atoms, indicating that atoms have internal structure.
4. Conclude that Thomson's discovery disproved Dalton's idea that atoms are indivisible, showing instead that atoms can be broken down into smaller subatomic particles.
5. Note that the other ideas from Dalton's theory, such as atoms combining in whole-number ratios and atoms not being created or destroyed in chemical reactions, were not disproved by this experiment.