Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Kryptid on 24/03/2004 18:13:16
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Anyone who has taken High School chemistry can tell you that the electrons in an atom exist in "atomic orbitals" that have a specific shape. These atomic orbitals come in different types, called s, p, d, f, and so on. The nature of these orbitals greatly affects the chemistry of that atom or molecule.
Now for my question: does the nucleus of an atom have "nuclear orbitals" that are occupied by protons and neutrons? If so, then what are the names and shapes of these orbitals? Since there is a "nuclear shell theory" for the atomic nucleus, it seemed to me that protons and neutrons should occupy certain energy states in the nucleus, rather than being stuck together randomly like textbooks often depict. It would be helpful if you could also supply me with a link to a webpage about nuclear orbitals.
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The nucleus is certainly not an analog of the electron shells in the atom on a smaller scale. The nuclear binding force has many orders of magnitude faster decay with separation than the electronic force's inverse square law. However, there does appear to be some analogous structure, and other structure as well that is not analogous.
You can Google "nuclear structure" and find a lot of hits. One especially cute one is here:
http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/nucstructcon.html#c1
The circles are interactive; click on them for a discussion.
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That is a cool link. It takes a while to wade through all of it, but it really helps tie things together.
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John - The Eternal Pessimist.
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Thank you for that. Another thing that concerns me is "magic numbers". They are 2,8,20,28,50, etc., but I don't see any particular pattern or formula that can be used to predict them. The electron structure of noble gases seems to be a predictable pattern: 2,8,8,18,18,32,etc., but not the magic shell numbers, even though both of them are considered to be "closed" and stable.
Is there any formula for magic numbers?
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There is a way to predict them. Quantum mechanics is pretty good at this. You can get a book on quantum mechanics and try to wade through it, but you're going to have to be pretty well steeped by the time you understand enough to derive the wave functions for multiple electrons in complex atoms. It's not terribly hard, just requires a lot of background to get there.
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John - The Eternal Pessimist.
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It seems like the consensus here is that nucleons do not have orbitals, and normally remain in a fixed position. I also have not had much luck in finding much information about nuclear orbitals on the wider web.
But today, a news article on sciencenews.org was released with the title "Physicists find atomic nucleus with a ‘bubble’ in the middle". The news article is about an paper in Nature Physics called "A proton density bubble in the doubly magic 34Si nucleus", and this paper is behind a paywall.
The news article states
"In their quirky quantum way, protons and neutrons in a nucleus refuse to exist in only one place at a time. Instead, they are spread out across the nucleus in nuclear orbitals, which describe the probability that each proton or neutron will be found in a particular spot."
The news article also states that one of the paper's findings was that the central nuclear orbital of Silicon-34 "held only 0.17 protons on average".
So, are/could nuclear orbitals be a real thing?
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So, are/could nuclear orbitals be a real thing?
Yes, nuclear shells are real.
But unlike Electron shells (just 1 particle), the nucleus is made up of 2 particles: Protons and Neutrons.
- The Protons and Neutrons have shells which fill up semi-independently.
- The "Magic" numbers described in the article are when a shell is completely full, which is more stable than a partially-filled shell.
- "Doubly Magic" refers to the case where the Proton shell is full, and the Neutron shell is also full (for heavier elements, the number of Neutrons > number of Protons).
See: https://en.wikipedia.org/wiki/Nuclear_shell_model
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I understand. So nuclear shells are definitely real.
So the remaining question is, do nuclear orbitals exist?
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Before we start talking about whether nuclear orbitals "really exist" some clarification is needed on what "really existing" means. For instance, those lovely shapes of electron/atomic orbitals (s, p, d, f etc.) that we are all familiar with aren't fundamental in any way. These shapes are convenient solutions (mathematically and intuitively), but there are infinitely many solutions (all of which are linear combinations of the same basis set). In fact that's why d orbitals have such funny names as x2-y2 and xz etc.
So are they "real"? well, they're useful. And assuming that they are real doesn't seem to lead to false conclusions... but I would say that orbitals are just a very good model. I don't know much about nuclear structure, so I can't speak to that in the same way that I can about atomic structure, but I would imagine that it is the same story: orbitals are useful, not demonstrably wrong, but not necessarily "real"...
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Electron orbitals have been imaged directly:
http://www.nature.com/nature/journal/v498/n7452/full/498009d.html
Electrons absolutely do adhere to the shapes that orbitals say they should. That makes them real enough for me.
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Electron orbitals have been imaged directly:
http://www.nature.com/nature/journal/v498/n7452/full/498009d.html
Electrons absolutely do adhere to the shapes that orbitals say they should. That makes them real enough for me.
Thanks for the link! This is an excellent study, and I agree that this shows the "real" radial distribution of electrons in different orbitals, but the distributions shown are still spherically symmetrical. As far as I know there is no "real" px, py, pz (after all, how does one define coordinates in an isolated atom?)
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That's an amazing set of images in that Nature paper; I am impressed!
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Electron orbitals have been imaged directly:
http://www.nature.com/nature/journal/v498/n7452/full/498009d.html
Electrons absolutely do adhere to the shapes that orbitals say they should. That makes them real enough for me.
What is the form of hydrogen used in the experiment? Is atomic or molecular?
If it is atomic, how to prevent them from forming diatomic molecule?
If it is molecular, how can it produce rotationally symmetrical pattern?
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Lets look at this a slightly different way. Electron orbitals are just the shape that the wave function of the electron takes on when bound to a nucleus. Therefore if the wave function of the electron is real then the electron orbitals should also be real. It would take some serious evidence to show the opposite.
There are certainly reasons to believe that the wave function is real. (https://www.newscientist.com/article/dn26893-wave-function-gets-real-in-quantum-experiment/)
At best you can say that according to some interpretations of Quantum Mechanics the wave function isn't "real/physical" but the question is unsettled. Although there is evidence pushing for the real camp.
Additionally,
The phase of a wave function (the complex bit) can have physical effects beyond just participating in the squared magnitude (the extra rotation of the photons in the link). (http://physicsworld.com/cws/article/news/2011/jun/15/catching-sight-of-the-elusive-wavefunction)
You can make qubits by exploiting the phase (imaginary) parts of wave functions. (https://en.wikipedia.org/wiki/Phase_qubit)
The things above and others like single particle diffraction and tunneling are less strange if you simply accept that the wave function is real.
But to reiterate one should never state as fact that the wave function is not real. At best the question is exactly as unsettled as the question about which interpretation is correct with a bit of evidence pulling for the wave function is real camp.
What is the form of hydrogen used in the experiment? Is atomic or molecular?
If it is atomic, how to prevent them from forming diatomic molecule?
If it is molecular, how can it produce rotationally symmetrical pattern?
It was atomic hydrogen. You can break a fraction of hydrogen molecules apart and keep that fraction constant by adding energy so more are broken at the same rate others reform. Then you can build a trap big enough for only one atom and eventually if you wait long enough you'll have a trapped hydrogen. If you keep the gas dilute enough collisions between things will be very rare.
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An electron is a negative charge in motion. The negative charge of an electron will generate an electro-static force. This force will repel all the other electrons in the atomic orbitals. However, since a charge in motion will also generate a magnetic force, the atomic orbitals shapes are helping to define magnetic force vectors, that can counter charge repulsion, allowing the electrons to attract each other.
For example, opposite spin electrons, in each orbital, will allow two electrons to magnetically attract. In the case of oxide; O-2, this stable anion can hold two more electrons than it has atomic protons. The filling in of p=orbitals (x,y,z); octet, allows additional magnetic attraction from the extras electrons, beyond the attraction coming from two less nucleus protons.
I would expect the nucleus protons to behave in the same way, since protons in motion would be able to generate magnetic attraction to help overcome positive charge repulsion. This magnetic attraction will be optimized if they moved in coordinated paths/shapes. The nuclear orbital shapes may or may not be the same as the electrons orbital shapes, but both benefit by electromagnetic addition.
Theoretically, one should be able to tweak a nuclear orbital and cause the electron orbitals to tweak, or vice versa. For example, magnetic iron alters the outer electrons positions, compared to nonmagnetic iron. In magnetic iron, outer electrons all have same spin whereas nonmagnetic iron will have some opposite spin for the same electrons. This could theoretically could a slight change in nuclear orbitals, to help stabilize this less than optimized electron arrangement.
Or theoretically one could induce extreme anionic states, which can alter the nucleus orbitals in ways that can cause nucleus reactions. Cold fusion may be connected to using electron orbitals, to tweak nucleus orbitals, so nuclear reactions can occur.
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Very nice explanation agyejy. The only thing I'm not happy with is 'weak measurements'. But I really liked this "The experiment relies on the quantum properties of something that could be in one of two states, as long as the states are not complete opposites of each other: like a photon that is polarised vertically or on a diagonal, but not horizontally. If the wave function is real, then a single experiment should not be able to determine its polarisation – it can have both until you take more measurements."
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Heh, found it Measurements on the reality of the wavefunction. (https://arxiv.org/abs/1412.6213)