Re: The Problem of the Missing Constant

"Timo A. Nieminen" <timo@xxxxxxxxxxxxxxxxx> wrote in message
news:Pine.WNT.4.64.0612231327200.756@xxxxxxxxxxxx
On Fri, 22 Dec 2006, hanson wrote:
http://groups.google.com/group/sci.physics/msg/d4ed61b44c2abd11

"Timo A. Nieminen" <timo@xxxxxxxxxxxxxxxxx> writes:
Measure atomic mass, [2] measure density of liquid; this should
give a reasonable estimate. The cool thing about atomic radii
is that they're almost all the same - the biggest atoms are only
about twice the radius of the smallest. [1]

[hanson]
Interesting! ... if so, then why is that so [1] when
their relative mass amount goes from 1 to ~250?

[Timo]
What does mass have to do with size of atoms?

[hanson]
ahahahahaha.. well, as you can see above, either you, Timo
or an earlier poster refered to a mass/size, radius relation [2]

[Timo]
Since Rutherford we know that the nucleus, with essentially all of the
mass, occupies an insignificant portion of the volume. The size depends on
the electrons, not the mass of the atom. OK, the number of electrons
depends on the number of protons, which generally increases with mass, but
what effect would neutrons have on the size?

Anyway, just do it with a simple Bohr model. Find the radii of the
innermost circular Bohr orbits for H and element 92 (ie, uranium).
Consider a uranium nucleus with with 91 Bohr electrons orbiting it. On
average, the 91 electrons screen 91 proton charges. Do you expect the
behaviour of electron 92 to be that different from electron 1 in H? [4]

The surprising thing is not that the heaviest atoms are only a little
larger than the lightest, but that they not smaller. [3]

[hanson]
That's actually a pretty good take. So you are saying that in all cases
(where) we do have a 1:1 +/- charge relation ship, overall neutrality
in atoms, we should expect same size roughly [3], in which case the
empirical facts are NOT surprising. In that case I can accept and
live with the assertion of "little larger" or "about twice"... ahahahaha...

However, if we add or remove any electrons [4] the situation changes
drastically as seen in the wide range of ionic radii with different Z.
---- But that's a different story .... and it leads now to yet another,
different but related story/issue, I wish you'd pontificate on:
If atoms have the size we see them to exhibit, roughly a constant
vs a vast range in the other variable (mass), then....
.....well, I'll back later on it, perhaps.... -- Take care and thanks,
Timo
hanson





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