# Why does an electron not fall into the nucleus?

Is it because the electron has less mass and is a point object that prevents it from falling into the nucleus due to attraction of protons?

Orodruin
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At the atomic level the electron is not a classical point object which can be thought of as "falling". It is described by quantum physics and it cannot be in a lower energy state than the ground state.

In quantum physics there is something called "the uncertainty principle" that states that we can't know where something is at the same time as we know where it's going (due to it being a wave). Or rather, the better known somethings position is, the less known is it's movement.

Now, with this knowledge we can determine what happens if an electron actually "fell" into the nucleus. The position would be well known (it's in the nucleus), but that means it could be moving really fast, so it breaks free from the nucleus again. This means it can't actually fall in.

Why we can't know where something is at the same time as we know where it's going due to it being a wave. How does being a wave effect this?

Orodruin
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Now, with this knowledge we can determine what happens if an electron actually "fell" into the nucleus. The position would be well known (it's in the nucleus), but that means it could be moving really fast, so it breaks free from the nucleus again. This means it can't actually fall in.
You need to stop using the word "fell", even within quotes. What you are describing is only a semiclassical and popular interpretation of quantum physics. The point is that if the electron was localised to the nucleus, it would be in a superposition of states which includes several non-bound states as well as some bound states which are bound but not the ground state. The time evolution of the wave function would quickly result in the electron most likely being somewhere else.

Why we can't know where something is at the same time as we know where it's going due to it being a wave. How does being a wave effect this?
This is also a popular misconception. Particles in quantum physics are not waves, nor are they tiny balls (i.e., classical particles). They have some properties reminiscent of these objects, but they really are quantum particles. The non-localisability of a quantum particle follows directly from the commutation relation between the position and momentum operators.

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Before going into the millionth near-identical copy of this thread, may I point out that this is the https://www.physicsforums.com/threads/why-dont-electrons-crash-into-the-nucleus-in-atoms.511179/ [Broken] in the https://www.physicsforums.com/threads/physics-faq-list.807553/ [Broken].

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I can understand that the electrons orbit the nucleus because there is a centripetal force exerted on the electrons. This centripetal force is due to the attractive force of the protons. But if we observe the Earth which orbits the sun. There is an initial momentum which stops Earth from moving into the sun. Does the electron also have some initial momentum?

Before going into the millionth near-identical copy of this thread, may I point out that this is the https://www.physicsforums.com/threads/why-dont-electrons-crash-into-the-nucleus-in-atoms.511179/ [Broken] in the https://www.physicsforums.com/threads/physics-faq-list.807553/ [Broken].

That's another topic. This question is not about a loss of energy doe to emission of EM-radiation but about an electron "falling" into the nucleus of an atom. The answer is, that the probability density of the electron is not zero in the nucleus of an atom and for s-electrons it even reaches its maximum in the center. Thus an electron can "fall" into the nucleus and proton-rich nuclei can capture it.

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Dale
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Does the electron also have some initial momentum?
It is possible for an electron to have an orbital with orbital angular momentum, but there are also orbitals without orbital angular momentum, called s orbitals. Since there are some orbitals without angular momentum, angular momentum is not the thing which prevents the electron from being confined to the nucleus.

In the end, it is just about energy. It would take a lot of energy to confine the electron to the nucleus. So instead it relaxes to a lower energy state where the electron is not confined to the nucleus.

Drakkith
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