Rutherford's atomic model 's limitation

  • #1
In Rutherford's atomic model, electrons are in circular orbit around nucleus. My teacher said, "It has limitation. According to classical electromagnetic theory, the electrons are acceration and they will emit radiation and lose energy. And finally spiral into nucleus. Th atom will collapse if Rutherford is correct. But in reality atom doesn't collapse so the model has limitation."

I get confused. Doesn't the electron orbit around the nucleus in reality? Why Rutherford is wrong ?
 

Answers and Replies

  • #2
Nugatory
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In Rutherford's atomic model, electrons are in circular orbit around nucleus. My teacher said, "It has limitation. According to classical electromagnetic theory, the electrons are acceration and they will emit radiation and lose energy. And finally spiral into nucleus. Th atom will collapse if Rutherford is correct. But in reality atom doesn't collapse so the model has limitation."

I get confused. Doesn't the electron orbit around the nucleus in reality? Why Rutherford is wrong ?

Your teacher is right; if electrons really were little teeny objects orbiting the nucleus just as the planets orbit the sun, then atoms would be unstable. And they aren't, so we know that model is not accurate. However, it is a very easy model to visualize, and it is good enough for a fair amount of practical physics... So the idea took hold in the popular imagination, and it's been there ever since.

Meanwhile, physicists of the late 19th century considered this to be one of their great unsolved problems: scattering experiments showed that atoms behaved as if they had a very small very dense positive-charged center surrounded by a very light positive-charged electrons; but no one could explain how such a structure could be stable.

It took the discovery of quantum mechanics to answer the question. No, electrons are NOT little teeny objects orbiting the nucleus just as the planets orbit the sun. If you want a reasonable visual/intuitive representation of what's going on, you can try searching Google images for "electron orbitals".
 
  • #3
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No, electrons are NOT little teeny objects orbiting the nucleus just as the planets orbit the sun.

And yet we have electron orbital magnetic dipole moment that is, or at least can be, derived by classical mechanics. So the question is how could such magnetic moment be created if electrons don't actually have continuous trajectories (in order to have velocity), but instead disappeared and popped up into existence from place to place.

In any case the average, or most probable, distance of electrons in certain shells is more or less constant, describing some circle, ellipse, sphere, or whatever other shape, with certain thickness. What I'd like to know is whether this orbital shell or probability cloud in Hydrogen atom lays in a plane or is distributed over sphere.
 
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  • #4
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What I'd like to know is whether this orbital shell or probability cloud in Hydrogen atom lays in a plane or is distributed over sphere.


Like I said, google for images of "electron orbitals"... But no, the probability distributions do not lie in a plane.
 
  • #5
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Like I said, google for images of "electron orbitals"... But no, the probability distributions do not lie in a plane.

It's hard to tell from 2D pictures. The thing is these orbital magnetic moments can have definite orientation, especially under influence of external magnetic field when they all align to point in the same direction.
 
  • #6
K^2
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MarkoniF, some orbitals have a net current, and therefore, a net magnetic moment. The distribution, however, is still 3-dimensional and looks nothing like classical orbits.
 
  • #7
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MarkoniF, some orbitals have a net current, and therefore, a net magnetic moment. The distribution, however, is still 3-dimensional and looks nothing like classical orbits.

When these orbital magnetic moments align to point in the same direction under influence of external magnetic field, as is the case with diamagnetic materials, what is it then that defines their orientation if not vector perpendicular to the plane of electron orbit? I know classical equations can be used to calculate both magnitude and orientation, what is equivalent QM equation for that?
 
  • #8
K^2
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It's a complicated enough problem. If you ignore thermal excitations, the valence orbitals will be in super-position that minimizes energy in magnetic field.
 

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