Electron cloud

[petrushka.googol]

Is the electron cloud a tangible entity or just a mathematical construct to aid in visualization?

 

Please advise.

[elfmotat]

There's no "cloud." The electron has a wave function which satisfies the Schrodinger equation, and the square of the wave function tells you the probability of finding an electron in any given region of space. No clouds necessary .

Edited October 8, 2014 by elfmotat

[ajb]

I would take it to be a way of describing the natural 'fuzziness' of quantum mechanics. You can't really pin the location of the electron down to a specific point. As elfmotat says, this is mathematically described by wave functions and the Schrödinger equation.

[Strange]

I have seen various experiments that image the structure of molecules - these appear to be entirely consistent with quantum theory.

 

For example, the pictures on this page:

http://gizmodo.com/5835164/fascinatingly-small-images-give-first-ever-glimpse-of-an-electrons-orbit

The upper images are actual molecules, the lower images are the theoretically predicted orbitals.

 

More here: http://www.nature.com/nchem/journal/v3/n4/full/nchem.1008.html

Edited October 8, 2014 by Strange

[studiot]

 

There's no "cloud."

 

That's a bit harsh.

 

You will find many so called "charge cloud" representations of molecules and atoms in monchrome in that classic textbook form Cambridge University

 

Stranks et al : "Chemistry A Structural View"

 

And a really beautiful colour one of uranium acetate on the front cover of

 

Petrucci : "General Chemistry"

Edited October 8, 2014 by studiot

[MigL]

If you try to visualize what the probability distribution would look like for non-trivial probabilities, it would probably be densest in a certain area and gradually diffuse out towards the edges, i.e. a 'cloud'.

Is it any wonder that images show the same ?

[Enthalpy]

The wave function is more than a way to predict the probability to interact with an electron if we were using some more accurate means.

 

First, it's a complex number with a phase, and this is fundamental for interferences, including when a particle has a complicated history before the intereference.

 

And then, many interactions involve a particle over all its delocalization volume. For instance the emission or absorption of a photon, or the interaction between two atoms, and so on. The absorption of a photon in a small place is just one special case, deducing a theory only from that it would lead to wrong concepts.

 

In pictures made by an atomic force microscope like Strange linked, the wave function is pretty much tangible.

 

One more idea in an "electron cloud" is that electrons can't be distinguished, so when representing a cloud, we sum the densities over all electrons (...and then the electrons are not independent, complicated world).

 

What's not intuitive: a particle is not only a wave. Its mass and charge spread as the squared wave amplitude would let calculate wrong results. One has to compute the behaviour of the particle with all its mass, charge and other attributes concentrated near every possible position.

[elfmotat]

 

That's a bit harsh.

 

You will find many so called "charge cloud" representations of molecules and atoms in monchrome in that classic textbook form Cambridge University

 

Stranks et al : "Chemistry A Structural View"

 

And a really beautiful colour one of uranium acetate on the front cover of

 

Petrucci : "General Chemistry"

 

Clouds are probably a bad way of thinking about it. As soon as we start introducing ambiguous words into the discussion there are bound to be misconceptions. If everyone sticks to discussion of states, wave-functions, amplitudes, and probabilities, then everything is well-defined and there is likely to be a concrete answer to whatever OP may ask. Once we introduce ambiguous terms like "cloud," inevitably we'll start getting nonsensical questions like, "can electron clouds precipitate(?)," or, "how do electron clouds condense?" Everyone's better off if we stick to the well-defined terminology.

[swansont]

That's a shortcoming of any analogy used in science. Analogies are sometimes necessary before people can grasp certain new concepts.

[studiot]

 

Clouds are probably a bad way of thinking about it. As soon as we start introducing ambiguous words into the discussion there are bound to be misconceptions. If everyone sticks to discussion of states, wave-functions, amplitudes, and probabilities, then everything is well-defined and there is likely to be a concrete answer to whatever OP may ask. Once we introduce ambiguous terms like "cloud," inevitably we'll start getting nonsensical questions like, "can electron clouds precipitate(?)," or, "how do electron clouds condense?" Everyone's better off if we stick to the well-defined terminology.

 

 

 

Oh come on, I hope you are just having an off day as this is a pretty condescending response.

 

Especially as your thesis is not even true.

 

We have all assumed that the 'electron cloud' has to to with quantum mechanics.

 

But in fact electron clouds do exist and such clouds provide one of the few analytical solutions we have managed to make for the solution of Poisson's equation.

(The field equations for a vacuum diode, including the space charge).

[elfmotat]

That's a shortcoming of any analogy used in science. Analogies are sometimes necessary before people can grasp certain new concepts.

 

Agreed. But the OP asked a question regarding whether the "electron cloud" is a "tangible entity," or just a way of visualizing things. I don't think he's looking for analogies.

 

 

 

 

Oh come on, I hope you are just having an off day as this is a pretty condescending response.

 

Especially as your thesis is not even true.

 

We have all assumed that the 'electron cloud' has to to with quantum mechanics.

 

But in fact electron clouds do exist and such clouds provide one of the few analytical solutions we have managed to make for the solution of Poisson's equation.

(The field equations for a vacuum diode, including the space charge).

 

That's a rather rude and accusatory response. Any "condescension" you interpreted was most likely projection. Do you have some sort of problem with me?

 

Yes we have indeed been talking about QM, which shouldn't be surprising. I'm not particularly impressed that the term "cloud" may be well-defined in some more obscure context, because I don't think it's particularly relevant to the OP.

[studiot]

Why do you consider vacuum diodes obscure?

[elfmotat]

Why do you consider vacuum diodes obscure?

 

"More obscure" meaning "specific," or "not very general." Diodes are not the general case for electrons, they are a specific case. And, in this thread, probably not very relevant. (I've also never seen them described by electron "clouds" either, so if you have a source for what you're talking about it would be appreciated.)

[studiot]

Where do you get the notion the OP was about the general case for electrons?

 

He specified 'electron cloud'

 

I admit I also jumped to the QM conclusion as can be seen from my first response, althought the term is more of a Chemists' one so I gave well respected Chemical references (from Cambridge University Press).

 

However I later realised that electron cloud could aldo refer to 'situations where electrons congregate'.

The space charge is one such and I'm sure anyone could dig up umpteen references to this effect from DeForest on.

I have detailed analyses in my EUP book Principles of Electronics by Gavin and Houldin (They devote a whole chapter to it)

Electronic Fundamentals and applications by Ryder (who specifically refers to the 'space charge cloud on p93 in his treatment of the space charge equation.

[MigL]

Play nice, boys.

I don't want to seem like I'm taking sides, elfmotat, as I have a great respect for your knowledge and opinion.

And while your suggestion would be great in a situation where everyone was as knowledgeable, unfortunately, sometimes wavefunctions, states and probabilities are above the level of new members, and even some of us others.

An analogy is sometimes useful in grasping a concept in order to proceed to amore advanced understanding.

[elfmotat]

Play nice, boys.

I don't want to seem like I'm taking sides, elfmotat, as I have a great respect for your knowledge and opinion.

And while your suggestion would be great in a situation where everyone was as knowledgeable, unfortunately, sometimes wavefunctions, states and probabilities are above the level of new members, and even some of us others.

An analogy is sometimes useful in grasping a concept in order to proceed to amore advanced understanding.

 

Before I got into physics I used to watch the usual pop-sci shows and documentaries, and I read the usual pop-sci books. So as you might imagine, I had quite a few analogies and simplified descriptions floating around in my head. Once I really started to learn physics I realized how very little I actually knew. All of the analogies and simplifications were actually very counter-productive for me; not only did I have to re-learn the basic concepts, but I had to un-learn all of the analogies to prevent myself from getting completely confused.

 

So maybe I'm biased, but I've always felt that being candid about what words and equations mean is the best course of action. Giving the OP, who is asking a very direct question, a less than honest answer would be a disservice to him. He doesn't understand? Great! Now he has something to learn! Feeding him half-truths to satiate his curiosity is bad - now he's not as curious, and he has a bad model in his head.