Question

Electrons present around the the nucleus carry negative charge whereas nucleus carry positive charge then why electrons do not fall in the nucleus?

Answer 1

The theory explained why an electron doesn’t fall into the nucleus. The answer was that the electron was already as close as it can get to the nucleus (when in the ground state). The evidence of his theory were the atomic spectra of the elements and Bohr had the correct equation for Hydrogen’s spectrum.

The theory predates the wavefunction however. After all, the electron doesn’t “orbit” the nucleus in the way a planet orbits a star. The electron is distributed in space* around a nucleus according to its wavefunction. The wavefunction is found by solving Schrodinger’s equation with a central electic potential.

The success (one of the many) of quantum mechanics was that it predicted the electron can occupy many states around a central potential, all with specific and discreet energies. Chemists call these states shells or orbitals. The theory correctly predicted quantization of an electron bound to a nucleus and correctly produced Bohr’s equation for Hydrogen’s atomic spectrum. Furthermore, the theory provided a framework to calculate the spectra of the other elements.

The theory predicts that there is a state with the lowest energy associated with it. This is the ground state and has a corresponding ground state wavefunction. That is, there is no solution to Schrodinger’s equation where the electron is found only exactly where the nucleus is. The evidence is that atoms interact with other atoms at distances much greater than the size of a nucleus. The electrons must be extending way beyond the nucleus for this to be the case.

Now, with all that said, there is a nuclear decay mechanism for unstable nuclei that are proton-rich compared to their neutron count. A proton will capture an inner-shell electron (most likely the ground state electron) and convert to a neutron. This is called internal conversion. However, if the electron could fall into the nucleus then I suspect we would be seeing even otherwise stable nuclei decaying in the same manner.

*All the electron wavefunctions are centered about the nucleus. In a sense, they have already “fallen” into the nucleus.

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