How did the discovery of the electron by J.J. Thomson change Dalton's model of the atom?

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Dalton’s theory of the atom was composed of the following postulates:

  • Matter consists of indivisible particles called atoms.
  • The atoms of the same element are the same.
  • Atoms can’t be created or destroyed.
  • Atoms combine in fixed, whole number ratios.
  • The atom is the smallest unit of matter involved in...

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Dalton’s theory of the atom was composed of the following postulates:

  • Matter consists of indivisible particles called atoms.
  • The atoms of the same element are the same.
  • Atoms can’t be created or destroyed.
  • Atoms combine in fixed, whole number ratios.
  • The atom is the smallest unit of matter involved in a chemical reaction.

The first postulate (shown in bold font) was proven incorrect by J.J. Thomson’s experiments. Thomson experimented with cathode ray tubes. He placed positively charged and negatively charged plates on either side of a cathode ray. Thomson discovered that the cathode ray bent towards the positively charged plate.

He concluded that the cathode ray must contain tiny negatively charged particles. These negatively charged particles were called electrons. The discovery of the electron showed that atoms are composed smaller particles. Thomson’s model of the atom stated that atoms are composed of diffuse positive charge with negatively charged electrons sprinkled throughout.

 

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