How to overcome the drawback of rutherford's model?

[Hardik Batra]

We, as high school students have been taught that-because Bohr's model of an atom assigns specific orbits for electrons-that it is better than Rutherford's model. But what Rutherford failed to explain was why electrons don't emit EM waves & fall into the nucleus. I don't see how the introduction of 'atomic orbitals' overcame this defect. Can't it still radiate EM waves?

 

[Nugatory]

The idea behind the Bohr model is that the electron cannot emit EM waves because they would take energy from the electron, but the electron cannot lose any of its energy because it is stuck in an orbital of fixed energy.

The Bohr model is as now as obsolete as the older Rutherford model; it was pretty much replaced by modern quantum mechanics about seventy-five years ago.

 

[Hardik Batra]

they would take energy from the electron,

what it meant to say?
they(electron) would take energy from the electron.

 

[ovais]

This is a very good question Hardik. I myself is looking for this from past 7 years. I asked this questions to many but never get a satisfactory answer. I even made a thread on PF here 6 years ago but it did not take me to some satisfactory answer. Hope this thread will quench the thirst of you as well as me. :)

Thread name: Conflict with atomic model. Asked in Oct, 2008. In fact that was my first thread of PF and I sign up on PF for this question. Many more difficult questions were answered but I am still looking for some unanswered questions and this is one these.

 

[DennisN]

what it meant to say?
they(electron) would take energy from the electron.

A classically orbiting electron around the nucleus would emit EM waves. EM waves carries away energy. This means the electron would lose energy, which would mean that the electron would spiral down and collide with the nucleus. All classically speaking, that is. This does not happen with e.g. the hydrogen atom, it is stabile.

EDIT:
See e.g. http://en.wikipedia.org/wiki/Bohr_model#Shortcomings
and also http://hyperphysics.phy-astr.gsu.edu/hbase/bohr.html#c6 for some more.

EDIT 2:
I just want to point out that what I wrote does not conflict with what Nugatory wrote above ;). What Nugatory wrote is correct.

 

[ovais]

The real question here is not whether (hydrogen) atom is stable or not. The question is why it is stable given that it is revolving around nucleus and that the electromagnetic theory is plain in saying that any accelerating charge particle DO lose energy. And when Bohr too said and accepted that electrons are revolving around nucleus therefore they are accelerating around positive charge nucleus. Now to prove that electron will not emit energy as it revolves around nucleus people (even of his time) need either to prove that electrons is/are not accelerating while revolving around nucleus or that the electromagnetism theory claiming that '' under such conditions electron(or a charge particle in general) emit energy '' is wrong theory and Bohr should get a noble prize for disproving such false theory. But texts and people keep on saying that as Bohr told us that as long as electron revolves around a define path or orbit it will not lose energy without bothering to tell how can this be true without the theory(of electromagnetism) being failed. I do respect all scientists but I don't think that any scientist or person do have any authority to change a fact if it does not seem fit in a particular situation unless it is not actually a fact but a human intuition.

 

[Nugatory]

they would take energy from the electron

what it meant to say?
they(electron) would take energy from the electron.

That was supposed to be "They (the EM waves) would take energy from the electron" .

 

[Drakkith]

I do respect all scientists but I don't think that any scientist or person do have any authority to change a fact if it does not seem fit in a particular situation unless it is not actually a fact but a human intuition.

No facts were ever changed. Bohr ignored the why and the how and just simply stated that electrons didn't fall from their orbits so he could have a basic working model that matched reality. It wasn't until quantum mechanics was developed that we knew why the electron doesn't emit radiation and fall into the nucleus. Classic EM theory turned out to be incorrect at the atomic scale.

 

[ovais]

No facts were ever changed. Bohr ignored the why and the how...

If he didn't change any fact( fact of his time; classical EM theory claiming that electrons DO emit radiation and should fall into nucleus) how can at the same time he talks contradictory to it for the sake of explaining stability of atom in Rutherford Model?

I guess if Rutherford himself had argued, like, `` No, my model of atom is alright while revolving around the nucleus my electrons(electrons of atoms) will not radiate any energy because I am going to assume that within a given orbit it's energy is going to be fixed, " in that case every person with a little sense would understand that Rutherford is making them fool(but the genuine scientist didn't act like this, rather he kept quiet for no answer.)

It wasn't until quantum mechanics was developed that we knew why the electron doesn't emit radiation and fall into the nucleus. Classic EM theory turned out to be incorrect at the atomic scale.

But Bohr didn't use quantum mechanics to correct the limitations of Rutherford Model of atom.
He just introduced that electron in a given orbit will not lose energy without looking at the gravity of the serious consequences of such statement at the first place. Means a direct consequence of his statement is invalidity of classical electromagnetic theory. And thus the classical EM theory should be considered incorrect from the date Bohr introduced his concept of fixed energy orbit. Why society of scientists had to wait to declare it incorrect till quantum mechanics later proved it wrong?

 

[Nugatory]

But Bohr didn't use quantum mechanics to correct the limitations of Rutherford Model of atom.
He just introduced that electron in a given orbit will not lose energy without looking at the gravity of the serious consequences of such statement at the first place. Means a direct consequence of his statement is invalidity of classical electromagnetic theory. And thus the classical EM theory should be considered incorrect from the date Bohr introduced his concept of fixed energy orbit. Why society of scientists had to wait to declare it incorrect till quantum mechanics later proved it wrong?

You are mistaken. Neither the Bohr atomic model nor the subsequent development of quantum mechanics invalidated classical E&M, which is still an essential piece of modern physics and engineering. Indeed, Bohr himself was using classical E&M to make his argument: "Classical E&M predicts that if an electron were in a classic Keplerian orbit around the nucleus, then certain phenomena would be observed. These phenomena are not observed, so it must be that the electron is not in a classical Keplerian orbit."

 

[ovais]

Neither the Bohr atomic model nor the subsequent development of quantum mechanics invalidated classical E&M, which is still an essential piece of modern physics and engineering.

If Bohr consider classical EM theory valid why he spoke* against it.

*( 1. Classical EM theory demands that an accelerating charge particle should emit radiation, right? 2. Bohr and Rutherford model of atom says electrons revolve around nucleus in circular(or near circular) orbits, right? Movement of electron in circular orbits means change in velocity, so electrons around nucleus undergoing change of velocity or having acceleration, right? 3. By saying such moving electrons not loosing energy the rule 1(classical EM theory) above is violated, isn't it? 4. So clearly Bohr is apparently secretly speaking against Classical EM theory)

"Classical E&M predicts that if an electron were in a classic Keplerian orbit around the nucleus, then certain phenomena would be observed. These phenomena are not observed, so it must be that the electron is not in a classical Keplerian orbit."

What is this classic Keplerian orbit? Honestly I never heard or read about it in any book I have, talking about this issue nor from any person except you.

It would be interesting to know (1)When, (2) by whom this term(classic Keplerian orbit) is introduced?

 

[Nugatory]

Enough already... The original poster's question has been answered, and ovais, you are arguing instead of trying to understand.