What keeps electron shells apart?

[dstebbins]

Electrons are negatively charged. Protons are positively charged. Opposite charges are supposed to attract, like a salt molecule.

 

However, even the densest of atoms - such as lead - are still >99% empty space. It's theorized that if the the entire human race - all 7 billion of us - eliminated all the space in our atoms, the entire human race would be less than a cubic inch in volume.

 

So why don't the electrons get attracted to the positively-charged nucleus, plowing into the nucleus like meteors?

 

When I was in 6th grade, I was told that it was their orbital speed ... like how an object on a string being swung in circles will keep the string tight and straight, which is called "centrivical force."

 

But that doesn't make any sense. How do the electrons keep their energy? When I'm swinging around an object on a string, my arm muscles are constantly feeding it energy. As soon as my muscles stop feeding it energy, it will either A) fly off in whatever direction it was pointing at the moment I released it, or B) slow to a stop as my arm muscles no longer cancel out the forces of gravity and air drag.

 

So that analogue, obviously, doesn't apply to elections.

 

So, how do electrons stay away from the nucleus and avoid creating atoms of sufficient density to form a black hole? If it really is their speed, then what keeps them energized?

[ajb]

Classically you are right. The electrons are accelerated and so would lose energy via electromagnetic radiation and spiral into the nucleus. However, quantum mechanics only allows the electrons to take specific energies and the Fermi exclusion principle states that only one electron per state eigenstate (allowing for degeneracy). In short the rules of quantum mechanics mean that atoms are stable.

[swansont]

IOW, once an electron state is occupied another electron isn't allowed in

[michel123456]

Classically you are right. The electrons are accelerated and so would lose energy via electromagnetic radiation and spiral into the nucleus. However, quantum mechanics only allows the electrons to take specific energies and the Fermi exclusion principle states that only one electron per state eigenstate (allowing for degeneracy). In short the rules of quantum mechanics mean that atoms are stable.

That is a constatation, not an explanation.

Quantum mechanics is not a force of nature.

[swansont]

That is a constatation, not an explanation.

Quantum mechanics is not a force of nature.

 

Bollocks. It's an explanation that requires some basic knowledge of physics.

 

In this case, how Fermi particles behave, which gives rise to the exclusion principle. Fermions are described by antisymmetric wave functions, and as they are identical particles there must be some difference in the state that they occupy. Otherwise, the total wave function for the system would be zero; the individual wave functions have opposite signs if you swap them. The state where all quantum values are the same doesn't exist.

[michel123456]

Bollocks. It's an explanation that requires some basic knowledge of physics.

 

In this case, how Fermi particles behave, which gives rise to the exclusion principle. Fermions are described by antisymmetric wave functions, and as they are identical particles there must be some difference in the state that they occupy. Otherwise, the total wave function for the system would be zero; the individual wave functions have opposite signs if you swap them. The state where all quantum values are the same doesn't exist.

A principle is not a force of nature.

Wave functions are descriptions, they are not a force of nature either.

 

I'd prefer an explanation that says that the electrons are indeed accelerated and that indeed they do spiral into the nucleus. Take that as a fact, and try to explain back why we are not able to observe anything of it. IOW to describe a collapsing universe from the inside.

[swansont]

A principle is not a force of nature.

Wave functions are descriptions, they are not a force of nature either.

 

I'd prefer an explanation that says that the electrons are indeed accelerated and that indeed they do spiral into the nucleus. Take that as a fact, and try to explain back why we are not able to observe anything of it. IOW to describe a collapsing universe from the inside.

 

But they don't. Why would you prefer an easily-understood explanation that is wrong?

 

"Forces of nature" is a rather simplistic view. Is energy conservation a principle, or a force of nature? There's nothing actively making energy be conserved, and yet it's true. It's a principle, and it tells us things about how nature behaves.

[michel123456]

I am not sure that would be an easily-understood answer.

If it is wrong, that's OK. You know better.

[swansont]

I am not sure that would be an easily-understood answer.

If it is wrong, that's OK. You know better.

 

If atoms exist then you should know it's wrong, too.

[michel123456]

Except if it is a Mandelbrot Electron.

[derek w]

An electron can't be smaller than it's wavelength.

The nucleus is smaller than the electrons wavelength.