# why not electrons fall into nucleus

if the velocity of an electron is decreased it goes near the nucleus in an atom....what if a photon hits the electron and the electron absorbs the energy of the photon...actually in nature, it uses the energy to increase the velocity and hence the radius increases and so the electron goes to a higher orbit...what in nature makes the electron to decide whether to use the energy to increase the velocity...why does it not use it to decrease the velocity instead and what if it makes the electron to fall into the nucleus...what will happen then???and why does this not happens??

Note by Mohammed Khan
5 years, 2 months ago

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There are two related questions in this thread.

1. Why does the electron not fall into the nucleus in general (with or without photons hitting it)?
2. Why does the earth not fall into the sun?

Let's deal with question 2 first. Who ever said the earth wouldn't fall into the sun? In fact, it would! The earth/sun system emits gravitational radiation, which makes it lose energy. Eventually the earth will spiral into the sun, but the timescale is very, very long. We actually had a problem about this on Brilliant a couple months ago.

Now, for question 1. Electrons orbiting the nucleus also should emit radiation if we think about them as classical objects similar to the earth moving around the sun. In fact the problem is even worse because since electrons are charged objects they'd emit a lot more electromagnetic radiation than gravitational radiation. Yet, atoms are stable! This problem was actually one of the first signals that our classical picture is just wrong. The orbits of electrons in an atom are governed by the laws of quantum mechanics and those dictate that one can't just slowly radiate energy away and make electrons spiral into the nucleus. See here for a lengthier discussion on this topic.

Staff - 5 years, 2 months ago

Why does an electron have a charge?

- 5 years, 2 months ago

That's a really great question!

The picture we often have of electrons as small objects circling a nucleus in well defined "orbits" is actually quite wrong. The positions of these electrons at any given time are not well-defined, but we CAN figure out the volume of space where we are likely to find a given electron if we do an experiment to look. For example, the electron in a hydrogen atom likes to occupy a spherical volume surrounding the proton. If you think of the proton as a grain of salt, then the electron is about equally likely to be found anywhere inside a ten foot radius sphere surrounding this grain, kind of like a cloud.

The weird thing about that cloud is that its spread in space is related to the spread of possible momenta (or velocities) of the electron. So here's the key point, which we won't pretend to explain here. The more squashed in the cloud gets, the more spread out the range of momenta has to get. That's called Heisenberg's uncertainty principle. Big momenta mean big kinetic energies. So the cloud can lower its potential energy by squishing in closer to the nucleus, but when it squishes in too far its kinetic energy goes up more than its potential energy goes down. So it settles at a happy medium, and that gives the cloud and thus the atom its size.

Hope its clear?

- 5 years, 2 months ago

hesienberg uncertainnity explain this if solve that hesienberg eq(xv = h\4pi) you will find that v cross the sped of light which is not possible . this is answer

- 5 years, 2 months ago

because the electron can occupy only quantized orbits. orbits are quantized cause it acts as a wave. Just like a vibrating string fixed at both ends cannot have any arbitrary wavelength. Why it acts like a wave is difficult to answer. many say cause u cant simultaneously measure position and momentum. I dont think thats completely correct. Quantum theory has many unanswered questions. Its triumph comes from explaining results than giving reason for why things are the way they are.

- 5 years, 2 months ago

Why earth does not fall on sun..?

- 5 years, 2 months ago

Earth just don't have those guts. Just kidding.

Earth needs to release some energy inorder to get closer to the sun which is not possible.

- 5 years, 2 months ago

due to hard core repulsive forces btween nucleus and electrons ,which act at a range of 0.5 fermi

- 5 years, 2 months ago

The electron has too much energy for it to fall into the nucleus classically. Even if the electron did "collide" into the nucleus, it would bounce right off as if nothing happened. More interesting phenomena does happen when an electron and nucleus interact, leading to a nuclear reaction or decay.

- 5 years, 2 months ago

i guess centrifugal force which is also calld pseudo force is the reason m nt confrm

- 5 years, 2 months ago

Electron's speed doesn't decrease as it goes closer to the nucleus, infact it increases.

- 5 years, 2 months ago

go and read ncert class ixth or xiith

- 5 years, 2 months ago