Re: "archaic" view of atom structure
From: Bjoern Feuerbacher (feuerbac_at_thphys.uni-heidelberg.de)
Date: 12/17/04
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Date: Fri, 17 Dec 2004 10:51:58 +0100
lindas4@aol.com wrote:
> Earlier today, I was told that the view of an atom as a nucleus with
> electrons in circular orbits was "archaic".
It is. It has been replaced in 1926, almost 80 years ago now.
> As I understand it (I am
> NOT a "card carrying physicist") this is, indeed a good, simplified
> view of the basic structure, and thus is useful for teaching and for
> calculations.
It is useful for *some* things (e.g. for the spectrum of hydrogen),
but fails miserably for most other effects.
It can be understood intuitively even by rather young pupils - but
I think the fact that one has to "unlearn" this model later when
one studies the *real* description makes it rather inconvenient
for teaching.
> In fact, this structure does occur.
Something similar to this occurs only for very highly excited
states of atoms (so-called Rydberg states). In atoms in their
ground states or lowly excited states, or in molecules, this
picture is simply wrong.
> For example, it is present in hydrogen and helium atoms.
Only in their Rydberg states.
> In atoms with a larger number of
> electrons, some electrons are forced into larger circular orbits, and
> some into elliptical orbits. Am I OK so far?
No.
> Also, as I understand it, the term "cloud" when used to refer to
> electrons and their behavior, simply refers to the fact that the
> electron, unlike a planet in the solar system, does not remain
> constantly in the same orbit,
No. It has no "orbit" at all!
> but moves away from and toward the
> nucleus as it travels around it (we all learned in elementary school
> science that heat will cause this to occur). Thus, the electron would
> look, to an observer, like a fuzzy cloud, and not like a clearly
> defined ring.
No, this has nothing at all to do with heat. Even at 0 K, the
electron should be pictured as a "cloud", not as a ball moving
in an orbit.
> Would a real "card carrying physicist", hopefully a physics instructor,
> please tell me if I am missing something here?
Well, I've already been a tutor for students of QM, so I hope
you will accept my authority. ;-)
Bye,
Bjoern
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