John Dalton's atomic theory proposed that atoms are indivisible and that all atoms of a given element are identical in mass and properties. However, J.J. Thomson's experiments with cathode rays in the late 19th century challenged the idea that atoms are indivisible.
Thomson discovered that cathode rays (now known to be streams of electrons) could be deflected by electric and magnetic fields, indicating that they were made up of smaller, charged particles. This demonstrated that atoms could be divided into smaller components (electrons), thereby disproving Dalton's claim that atoms are indivisible.
In summary, Thomson's cathode ray tube experiments disapproved the part of Dalton's theory that stated that atoms are indivisible.
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