What keeps electrons from falling into the nucleus of an atom?



At the intra-atomic level, classical mechanics and electromagnetism are no longer valid: electrons are not balls that orbit around the nucleus, they are more aptly described  by a probability distribution. So it’s necessary to analyse this systems’ behaviour using quantum mechanics. Therefore:

  • Bound systems can exist only for discrete values of energy —as per Schrödinger equation.
  • The ground-state (lowest-energy state) can’t correspond to a stationary particle state —as per the uncertainty principle.

This implies that the electrons’ ground-state can’t be the one that corresponds to electrons “fallen” in the nucleus. Consequently, their ground-state should have higher energy, that coincides to a state at finite distance from the nucleus. 

In other words: there are energy levels forbidden to an electron and the level that would coincide with the nucleus is one of these.

Image: [x]  –  Asked by dolems


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