[shreyas]

 it could not explain thestability of the atom. According to the electromagnetic theory ofradiation, a moving charged particle, such as the electron which
is constantly accelerating because of change in directions of motion, should emit radiation. The energy of the radiation would come from the motion of the electron. Thus, the electron would emit radiation and follow a spiral path ..

NOW MY DOUBT--But in real also the electrons revolve around the nucleus....then also they do not fall in the nucleus because of losing energy..or do the electron move very slowly around d nucleus...

[cth]

NOW MY DOUBT--But in real also the electrons revolve around the nucleus....

If you have in mind the picture of a planetary-based system with electrons turning like little planets around the nucleus, we know with quantum physics that this representation is wrong. OK, it is a pretty model easy to understand for students starting chemistry, but it is also largely oversimplified to a point of being just wrong.

I don't know how much you've been taught about quantum physics if any at all. To make it simple:
   - the energy an electron can have is not continuous, it can only take some specific values. Once in the lowest allowed energy level, the electron can't loose anymore energy and can't crash onto the nucleus as it would with the Rutherford's model.
   - it is impossible to measure accurately both the electron position and speed. Therefore, there are always some uncertainty when describing its motion: we can only know where the electron is moving with a certain probability. As a result electrons are not orbiting around the nucleus following a well defined ellipse as the Rutherford's model implies (that would go against the intrinsic uncertainty), but they are occupying a volume of space around the nucleus where we have a nonzero probability to find the electron somewhere inside.

[nj_bartel]

This always confused me.  Is there a logical reason the electrons' orbits don't eventually decay into the nucleus?

[Borek]

Not sure if it classifies as logic, but you just can't describe electron in the molecule/atom as a moving particle. We are beyond applicability of the classic description, so its conclusions are incorrect as well.

Electron is no longer a particle, it is a wave. Standing wave to be more precise. And as such it requires completely new treatment.

Think about elasticity and Young modulus. For low stress elasticity is linear. Once you get past some value, you need completely different description of the elongation. That's not much different conceptually, applicablity of one model ends, you need another model.

[cth]

Not sure if it classifies as logic, but you just can't describe electron in the molecule/atom as a moving particle. We are beyond applicability of the classic description, so its conclusions are incorrect as well.

Electron is no longer a particle, it is a wave. Standing wave to be more precise. And as such it requires completely new treatment.

This is true not only for electrons inside atoms, but it is true at all time: every particle has an associated wave. The duality wave/particle is the reason of being of quantum physics.

This always confused me.  Is there a logical reason the electrons' orbits don't eventually decay into the nucleus?

If you think about what happens inside neutron stars where gravity is so unthinkably strong that it forces electrons to merge with protons forming neutrons, it tells you that an electron decaying inside the nucleus is possible. However, it requires a fantastic amount of energy. This energetic barrier makes it extremely unlikely to have an electron tunnel inside a nucleus, fortunately for us . But I don't know where or why this barrier originates from.

[nj_bartel]

Thanks

[Borek]

an electron decaying inside the nucleus is possible. However, it requires a fantastic amount of energy. This energetic barrier makes it extremely unlikely to have an electron tunnel inside a nucleus

Actually it not only happens, but is much more likely that you seem to be thinking

http://en.wikipedia.org/wiki/Electron_capture