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In the Geiger-Marsden Experiment, I get how he knew that the nucleus was positively charged, and I'm assuming he knew it was small because the scattering through large angles only happened every 8000 times. However, how did Rutherford know that the electron's orbited? Couldn't he just say the electrons stayed in the empty space.

Also how did he know that most of the mass resided in the nucleus? Is it fair to say since Milikan determined the charge of an electron, and hence using JJ Thomson's q/m ratio, Milikan knew the mass. And hence since the mass of the electron was so small, could Rutherford conclude that most of the mass resided in the nucleus?

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Couldn't he just say the electrons stayed in the empty space?
The attractive electrostatic force between the positive nuclei and the negative electrons has to be accounted for. So have the electrons orbiting the nuclei under the effect of the attractive electrostatic force like the planets orbit the Sun because of the attractive gravitational force.

Also how did he know that most of the mass resided in the nucleus?
There was no evidence of the nuclei recoiling when interacting with the incoming alpha particles which indicated that the mass of a nucleus was much larger than that of an alpha particle.

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  • $\begingroup$ On the second point, the recoil energy of the alpha was compatible with the kinematics of a recoil off a mass equal to a gold nucleus. This was tested (successfully) with scattering probabilities and energies off of foils of different elements. One could suggest that, in fact, they indirectly observed the target nucleus recoiling just the right amount. $\endgroup$
    – Jon Custer
    Commented Oct 1, 2021 at 13:38
  • $\begingroup$ @JonCuster Yes, I accept your point and the later target foils were made of lighter element nuclei which would show more of a recoil. $\endgroup$
    – Farcher
    Commented Oct 1, 2021 at 16:23
  • $\begingroup$ @farcher,the difference I noticed is that in sun planetary model,planets cannot repell each other,hence if they had no velocities,they would smash into each other,while,electrons repell each other,why didn't they think that static electrons can cause stable atom with electronic configuration like positve nucleus attracting electron,while other electrons repelling each other to not allowing to be too close to each other,hence causing equillibrium? $\endgroup$ Commented Sep 12, 2023 at 21:43

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