Please allow me to clarify my question.

According to my understanding of charges, like charges repel and opposites attract.

Therefore protons and electrons should attract one another.

So what is the source of the force that keeps protons from attracting electrons in the nucleous?

There are no electrons in the nucleous, so there is no force keeping the electrons in the various orbitals from entering the nucleous. Why does it no do this?

I think the discussion has wandered a bit from your original question which I write as

"as the electron and proton have opposite electrical charge they will experience an attractive force. Why does the electron not plunge into the nucleus as a result of this force?"

This question has to be tackled on two levels: 1) classical mechanics, 2) quantum mechanics

**Classical answer**If the proton and electron are initially stationary relative to each other then the electrostatic attraction will pull them together

To avoid this fate for the electron we say the electron orbits the proton/nucleus. Why? Because by analogy with planets orbiting stars under the influence of gravity. The planets follow a near circular orbit around the star. Why? The gravitational attraction between the objects plus the perpendicular velocity of the planet means the surface of the star "Falls away" from the planet as soon as the planet tries to reach it. Notice, there must be the horizontal velocity of the planet relative to the star for this to happen.

By analogy the nucleus is pulling the moving electron into a circular orbit around it.

So why doesn't this explanation work for electron/proton systems?

Because according to Faraday (Maxwell?) laws the electron is not following a straight path, therefore it is accelerating therefore it must emit electromagnetic radiation therefore it loses energy as it travels therefore it will eventually fall into the nucleus.

We don't observe this gradual loss of energy (*) so something about this model must be wrong. (*I can't do the sum but I guess this loss of energy would happen so quickly that atoms would not be stable and matter could not exist if this model was correct.)

**(Simplistic) quantum answer**The Bohr model of the atom

http://en.wikipedia.org/wiki/Bohr_model states the electrons around a nucleus can only occupy certain energy levels. The electrons cannot exist in any other energy level relative to the nucleus. Further the electrons can only move between energy states by absorbing or releasing exactly the right energy amount (the energy is electromagnetic). The evidence for this exact transition is in absorption/emmission spectra and black-body radiation.

This explanation says nothing about where the electron actually

**is** in relation to the nucleus. In fact Heisenberg

http://en.wikipedia.org/wiki/Heisenberg_uncertainty showed you cannot be exactly accurate about both the position and the velocity/momentum/k.e. of the electron. So why is that relevant? Well, the experimental observations and the mathematics show us that we can only calculate a probability for where the electron

**could** be. We can calculate a region around the nucleus where with 90% or 95% or 99% probability the electron could be (wave mechanics I think needed). Now ... it turns out that the probability the electron can be in the nucleus is zero - look at the chemguide diagram for the 1s orbital.

So ... the electrons can only inhabit certain energy levels and not one of those has a probable location that is in the nucleus. There is no allowable "jump" of the electron from "outside" the nucleus to "inside" the nucleus - so the electron just can't get there. There isn't an explanation as to

** why** that is so - it is just the mathematics exactly model the observed behaviour and our interpretation is (something) like what I have written above.

You have to abandon the classical model and embrace the quantum model otherwise you can't explain the behaviour that is observed when experiments are done on electrons and atoms.

Clive