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Author Topic: Why aren't electrons in the nucleus?  (Read 10498 times)

Offline thedoc

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Why aren't electrons in the nucleus?
« on: 04/06/2015 21:50:02 »
Atul sharma asked the Naked Scientists:
   
Why is it not that electrons bind together by the nuclear force and reside inside it, and protons move along around it?

What do you think?
« Last Edit: 04/06/2015 21:50:02 by _system »


 

Offline alancalverd

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Re: Why aren't electrons in the nucleus?
« Reply #1 on: 04/06/2015 23:29:54 »
Because "electron" is the name we give the the negatively charged particles on the outside of an atom, and "proton" is the name we give to the positively charged particles in the middle.

And the words "positive" and "negative" are equally arbitrary.

There is no "why" in physics. We name the constituent bits of the universe, and construct mathematical models of "how" it works.
 

Offline syhprum

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Re: Why aren't electrons in the nucleus?
« Reply #2 on: 05/06/2015 00:43:19 »
In the old days you had Electrons inside the nucleus but QM does not allow it except in Neutron stars
 

Offline jccc

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Re: Why aren't electrons in the nucleus?
« Reply #3 on: 05/06/2015 04:44:14 »
anti matter?
 

Offline PmbPhy

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Re: Why aren't electrons in the nucleus?
« Reply #4 on: 05/06/2015 06:48:34 »
Quote from: thedoc
Why is it not that electrons bind together by the nuclear force and reside inside it, and protons move along around it?
Because the nucleus has much more mass than electrons do. Objects with greater mass orbit the center of mass of the system further out than other objects of less mass. If the mass of one object is significantly greater than the other then the object then that object will remain almost at rest close to one point. This happens for the same reasons that the planets orbit the Sun which remains at rest at the center of our solar system.
 

Offline jccc

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Re: Why aren't electrons in the nucleus?
« Reply #5 on: 05/06/2015 07:32:32 »
Quote from: thedoc
Why is it not that electrons bind together by the nuclear force and reside inside it, and protons move along around it?
Because the nucleus has much more mass than electrons do. Objects with greater mass orbit the center of mass of the system further out than other objects of less mass. If the mass of one object is significantly greater than the other then the object then that object will remain almost at rest close to one point. This happens for the same reasons that the planets orbit the Sun which remains at rest at the center of our solar system.

so the electron does circling the proton in a hydrogen atom?

is the electron orbital 2 d or 3 d?

Thanks! Good morning!
 

Offline alancalverd

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Re: Why aren't electrons in the nucleus?
« Reply #6 on: 05/06/2015 08:55:55 »


so the electron does circling the proton in a hydrogen atom?

is the electron orbital 2 d or 3 d?

Thanks! Good morning!

You are, as always, confusing the "classical" Bohr model with the quantum model. Orbitals are 3 dimensional probability density maps. The electron does not "circle" the proton, which is why we use the word "orbital" and not "orbit".
 

Offline jccc

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Re: Why aren't electrons in the nucleus?
« Reply #7 on: 05/06/2015 10:29:55 »
please explain the details.

what is propability density map?  do we have a pdm for solar system?

we are talking science right?

1 proton and 1 electron, how the hydrogen atom is formed?
 

Offline evan_au

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Re: Why aren't electrons in the nucleus?
« Reply #8 on: 05/06/2015 12:19:39 »
Quote from: jccc
anti matter?
As jccc says, you could make an atom out of an anti-proton (which has a negative charge), and an anti-electron (which has a positive charge; it is also called a positron).

In this case, the positive charge would circle around the negative center.

As PmbPhy says, the anti-proton is much more massive than the positron (by a factor of almost 2000 times), so you could imagine the negative nucleus as staying stationary*, and the positive orbital surrounds it.

* In reality, there is nothing really stationary in relativity or quantum theory.
 

Offline PmbPhy

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Re: Why aren't electrons in the nucleus?
« Reply #9 on: 05/06/2015 16:55:17 »
Quote from: jccc

so the electron does circling the proton in a hydrogen atom?
Nope. I never used the term "circle." I said "orbit." I.e. that's why there are electron orbitals instead of proton orbitals.

You really need to start paying attention to what you read.
 

Offline jccc

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Re: Why aren't electrons in the nucleus?
« Reply #10 on: 05/06/2015 17:02:11 »
what's difference between circle and orbit?

is hydrogen atom's electron orbital 2 d or 3 d?

what's the mechanism?

Thanks!
 

Offline PmbPhy

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Re: Why aren't electrons in the nucleus?
« Reply #11 on: 05/06/2015 19:10:04 »
Quote from: jccc
what's difference between circle and orbit?
Pick up a text on quantum mechanics and learn the difference. I've told you the difference so many times now that I'm sick to death of it and it's clear that you'll never learn it until you stop being a spoiled brat and do the adult thing and learn physics the right way, like the rest of us who do understand it. The other way, by asking questions and paying attention to the answers, doesn't work for you as you've proved to us many times.
 

Offline PmbPhy

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Re: Why aren't electrons in the nucleus?
« Reply #12 on: 05/06/2015 20:10:42 »
Quote from: alancalverd
There is no "why" in physics.
Nice!  :)
 

Offline jccc

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Re: Why aren't electrons in the nucleus?
« Reply #13 on: 06/06/2015 12:57:18 »
Quote from: alancalverd
There is no "why" in physics.
Nice!  :)

really?  [B)]
 

Offline lightarrow

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Re: Why aren't electrons in the nucleus?
« Reply #14 on: 06/06/2015 13:34:19 »
I had a series of discussions with an old, retired electron, sometimes ago, and he used to say that he always see a proton orbiting round him, when he worked in the hydrogen-atom firm.
 ;D

--
lightarrow
« Last Edit: 06/06/2015 13:35:51 by lightarrow »
 

Offline PmbPhy

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Re: Why aren't electrons in the nucleus?
« Reply #15 on: 06/06/2015 13:36:26 »
Quote from: jccc
really?  [B)]
There are different views on this. Quite often science can't supply answers to "why" questions. However many scientists think that the goal of science is to provide answers to such questions. As Mendel Sachs explains in his text Concepts of Modern Physics: The Haifa Lectures on page 4
Quote
Though some scientists believe that the descriptive level of science is all that there is to know, that is, they believe that scientists
should only ask ‘what’ questions, I believe that the explanatory level that follows the descriptive level is the actual goal of science — the answers to the ‘why’ questions.
Experience tells me that more often than not science has only provided what questions. However there is a place for why questions in science too such as Why is the sky blue? and Why does the Earth have a magnetic field? etc. Those questions have answers.

And of course I've explained all of this to you before and like everything else, you forgot about it.
 

Offline jccc

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Re: Why aren't electrons in the nucleus?
« Reply #16 on: 06/06/2015 15:00:02 »
I had a series of discussions with an old, retired electron, sometimes ago, and he used to say that he always see a proton orbiting round him, when he worked in the hydrogen-atom firm.
 ;D

--
lightarrow

which orbital was he in charge?
 

Offline alancalverd

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Re: Why aren't electrons in the nucleus?
« Reply #17 on: 08/06/2015 11:58:03 »
I guess there are two colloquial interpretations of "why". One is indeed asking for an elucidation of mechanism, and "why is the sky blue" is less clumsy than "what mechanism can you propose and test that would make the atmosphere appear blue when illuminated by the sun and viewed from below?" but that's quite different from a "philosophical" why, which seeks an ulterior motive for things being as they are.

The third interpretation is known as the "jccc question". You take an absurd proposition and ask why it isn't true. This form of "why" seems particularly common on science forum boards, and the answer is often "because the implied question is absurd".  The implication is "why is the sky blue when according to my calculations it should be red" - in other words, the answer lies in the realms of psychology: delusions of grandeur or omniscience, etc.

As always in physics, if the world doesn't meet your expectations, your expectations are wrong.
 

Offline lightarrow

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Re: Why aren't electrons in the nucleus?
« Reply #18 on: 08/06/2015 17:57:19 »
I had a series of discussions with an old, retired electron, sometimes ago, and he used to say that he always see a proton orbiting round him, when he worked in the hydrogen-atom firm.
 ;D

--
lightarrow

which orbital was he in charge?
He didn't remember the exact name because he kept changing to higher levels, but he remembered that the last one had n = 137 and that he were in a "Rydberg" atom:

http://en.wikipedia.org/wiki/Rydberg_atom
Quote
The similarity of the effective potential ‘seen’ by the outer electron to the hydrogen potential is a defining characteristic of Rydberg states and explains why the electron wavefunctions approximate to classical orbits in the limit of the correspondence principle.[3] In other words, the electron's orbit resembles the orbit of planets inside a solar system, much like the obsolete but visually useful Bohr and Rutherford models of the atom used to show.

--
lightarrow
« Last Edit: 08/06/2015 18:02:28 by lightarrow »
 

Offline alancalverd

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Re: Why aren't electrons in the nucleus?
« Reply #19 on: 08/06/2015 20:06:52 »
Google "f orbital shapes" to see just how wrong the "planetary orbit" model is.
 

Offline lightarrow

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Re: Why aren't electrons in the nucleus?
« Reply #20 on: 09/06/2015 00:19:39 »
Google "f orbital shapes" to see just how wrong the "planetary orbit" model is.
Are you answering me? If you do, I have to inform you that you haven't read carefully what I've written and the wiki link.
I repeat: in Rydberg atoms, orbitals can really be almost classical orbits.
Electrons behave almost classically there. Have you ever heard of "classical limit"?

--
lightarrow
 

Offline Bill S

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Re: Why aren't electrons in the nucleus?
« Reply #21 on: 09/06/2015 00:31:00 »
Quote from: Jccc
what's difference between circle and orbit?

My understanding is that the only real difference is that most natural orbits are not quite circular.  However, I think the question you may have meant to ask was "what's difference between circle and orbital?"

The answer to that is in #6 and probably in several other places.
 

Offline PmbPhy

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Re: Why aren't electrons in the nucleus?
« Reply #22 on: 09/06/2015 05:54:30 »
Quote from: syhprum
In the old days you had Electrons inside the nucleus but QM does not allow it except in Neutron stars
What do you mean by "the old days"?

Some orbitals don't have a zero probability density of being inside the nucleus. Is that what you mean? In situations like neutron stars the electrons combine with the protons to form neutrons. However a neutron is not a proton with an electron inside of it.

Quote from: jccc
what's difference between circle and orbit?

is hydrogen atom's electron orbital 2 d or 3 d?

what's the mechanism?

Thanks!
God damn it, jccc! I fail to understand why you can't do what we all do and that's to look it up in Google if we don't know the answer or its not in one of my textbooks on physics.

From Wolfram - A circle is a geometric entity, i.e. a circle is the set of points in a plane that are equidistant from a given point O. An orbit i

From Wikipedia - An orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System.

re - is hydrogen atom's electron orbital 2 d or 3 d?

Here we go yet again explaining things you should already know but don't because you're too damn lazy to read and have to be spoon fed like an infant. Again, your confusing orbital with orbit. They are entirely different concepts. A hydrogen atom has many orbitals associated with it. The "2" or "3" corresponds to the energy level of that electron while the "d" represents l, the angular momentum quantum number corresponding to l = 2.  See http://en.wikipedia.org/wiki/Atomic_orbital
 

Offline Bill S

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Re: Why aren't electrons in the nucleus?
« Reply #23 on: 09/06/2015 10:59:24 »
Quote from: Pete
What do you mean by "the old days"?

Wasn't there a time when the atom was thought (by some?) to be a lump of positive matter with negative inclusions, like currents in a pudding?
 

Offline PmbPhy

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Re: Why aren't electrons in the nucleus?
« Reply #24 on: 10/06/2015 13:41:15 »
Quote from: Bill S
Quote from: Pete
What do you mean by "the old days"?

Wasn't there a time when the atom was thought (by some?) to be a lump of positive matter with negative inclusions, like currents in a pudding?
Yup. It was called the plum pudding model, hypothesized by  J. J. Thomson in 1904.

http://en.wikipedia.org/wiki/Plum_pudding_model

In particular I was asking what he means by the old days since there were various steps to a complete theory of quantum mechanics.
 

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Re: Why aren't electrons in the nucleus?
« Reply #24 on: 10/06/2015 13:41:15 »

 

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