Electrons and Thomson's Model of an Atom

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13 Questions

According to Thomson's Model of an Atom, what did he compare the electrons to?

Black seeds in a watermelon

What is the charge of an electron?


What type of particles does radioactivity involve giving out?

Alpha and beta particles

In Rutherford's Experiment, what particles were used and directed towards a thin gold foil?

Fast-moving alpha (α)-particles

What did Rutherford conclude about the distribution of positive charge in an atom?

Concentrated in a very small volume

What was one of the major observations from the Gold Foil Experiment?

A major fraction of α-particles passed through without deflection

Why did Rutherford's model of the atom face a drawback according to the text?

The atom would be unstable due to electrons losing energy and falling into the nucleus

What was the purpose of Millikan's Oil Drop Experiment?

To measure the charge of an electron

According to Bohr's model, where do electrons revolve around in an atom?

In stable orbits without losing energy

What did Rutherford conclude about the size of the nucleus compared to the overall size of an atom?

The nucleus is very small compared to the atom

What were the major observations made by Rutherford in the Gold Foil Experiment and what conclusions did he draw from them?

Major observations: Most alpha-particles passed through the gold foil, some were deflected by small angles, and a few were deflected back. Conclusions: Atoms have mostly empty space, positive charge is concentrated in a small nucleus, and electrons revolve around the nucleus in defined orbits.

Explain the drawbacks of Rutherford's model of the atom and how Bohr's model addressed these drawbacks.

Drawbacks of Rutherford's model: Electrons in circular orbits would lose energy and collapse into the nucleus. Bohr's model overcame this by proposing stable electron orbits without emitting radiant energy.

Describe the significance of Millikan's Oil Drop Experiment and what conclusion was drawn regarding the charge of an electron from this experiment?

Significance: Millikan's experiment measured the charge of an electron, showing it is quantized. Conclusion: The charge on any particle is an integral multiple of the elementary charge (1.6*10^-19 C).

Study Notes

Sub-Atomic Particles

  • Electrons are negatively charged sub-atomic particles of an atom with a negligible mass and a charge of -1, symbolized as e–.
  • Electrons are extremely small and found outside the nucleus.

Thomson's Model of an Atom

  • According to Thomson, an atom consists of a positively charged sphere with electrons embedded in it.
  • The negative and positive charges are equal in magnitude, making the atom electrically neutral as a whole.
  • Thomson's model is often compared to a Christmas pudding or watermelon, where the positive charge is the edible part and the electrons are the seeds.


  • Radioactivity is the process by which an unstable nucleus loses energy by emitting particles such as alpha and beta particles.
  • This process occurs spontaneously due to an imbalance in the protons and neutrons in the nucleus, making the atom unstable.

Rutherford's Experiment and Observations

  • Rutherford's experiment involved bombarding a thin gold foil with fast-moving alpha particles to study the structure of the atom.

Learn about electrons, the negatively charged sub-atomic particles of an atom, and Thomson's Model of an Atom which describes an atom as consisting of a positively charged sphere with embedded electrons. Understand the properties of electrons and how they contribute to the overall charge neutrality of an atom.

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