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How did Dalton's atomic theory change after the discovery of subatomic particles?

Dalton's atomic theory was composed of the following postulates:


  • Matter is composed of individual particles called atoms.

  • Atoms of the same element have the same mass and are different from atoms of different elements.

  • Atoms can't be created or destroyed.

  • Atoms can combine in different ratios to form compounds.

  • Atoms are the smallest unit of matter involved in chemical reactions.

In 1897, J. J. Thomson conducted a series of experiments using cathode rays. Thomson's experiments indicated that atoms were composed of smaller, negatively charged particles. These particles were later called electrons. Electrons were the first subatomic particles to be discovered. Other subatomic particles, including protons and neutrons, were later discovered. 


The discovery of subatomic particles proved that the first of Dalton's postulates was incorrect. The discovery of subatomic particles proved that atoms were not indivisible. Dalton's actual model of the atom was uncharacterized other than to suggest that atoms were the building blocks of matter. Thomson's experiments changed the model of the atom to one containing positively and negatively charged particles dispersed throughout. 

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