Question

state the drawbacks of rutherfords atomic model

Answer 1

Well, the biggest is probably that it was not consistent with the physics of the day (classical mechanics). In Thomson's "plum pudding" model, for example, it was possible to imagine that the negative electrons were embedded in a positive matrix, and that the combination of attractive and repulsive forces kept the atom stable, just like the positive and negative ions in a cystal of an ionic solid are stable.

In Rutherford's model, however, the electrons were NOT in contact with the positive parts of th atom, the nucleus. But what kept them away? Obviousy not electrostatics, because they would experience only attractive forces, pulling them towards the nucleus. It can't be the repulsive forces of direct contact. Could it be repulsive forces from other electrons? Maybe...but that's asking a lot, to have the electrons just hovering in a particular arrangement that works out to keep them all in place by balancing attractive and repuslive forces. What's to stop one from being bumped out of place, and then all of them crashing into the nucleus?

The last possibility is that the electrons are in orbit around the nucleus, that is, that they're moving, and their motion keeps them from crashing into the nucleus, just as the Moon's orbital motion keeps it from crashing into the Earth, despite the attractive gravitational force between them.

But this runs into the severe problem that the electrons would then necessarily be accelerating (acceleration is any change in velocity, and if the velocity is continually bending around in a circle, so the particle can go in a circular path, then the particle is continually accelerating). And an accelerating electric charge must radiate electromagnetic energy in the form of light or radio waves. But if the electrons were radiating energy, they would slow down, because the energy must come from somewhere, and the only place from which it can come is the motion of the elecrtons. But if they keep slowing down, they'll eventually fall into the nucleus.

So the Rutherford model was considerably less consistent with the physics of the day than was the Thomson model. It's a sign of the power of empirical scienec that, nevertheless, it was given very serious consideration, based on the results of the Geiger-Marsden experiment. Because to good physicists, an ounce of experimental observation is worth a ton of theory. Physicists worked on modifying the theory to account for Rutherforrd's experimental observations. The result was the far-reaching changes that gave us a new theory of mechanics, quantum mechanics.

Answer 2

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