Understanding Atomic Radii: Average Figures or Unclear Measurement?

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    Atomic Atomic radii
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Discussion Overview

The discussion revolves around the concept of atomic radii, specifically whether the figures provided in tables of elements represent average values and how isotopes may influence these measurements. Participants explore the definitions and implications of atomic radii in relation to isotopes, as well as the clarity of available resources on the topic.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants question whether the atomic radii figures in tables are averages, noting a lack of clarity in how these measurements are presented alongside relative atomic masses.
  • One participant suggests that atomic radii are defined by electronic structure and proposes that isotopes, having the same electron configuration, likely have the same atomic radius.
  • Another participant references discrepancies in sources, indicating that some encyclopedias claim isotopes have different radii but do not provide specific figures.
  • A suggestion is made to research Rydberg atoms, which can have significantly larger radii than normal atoms, to illustrate the variability in atomic size under different conditions.
  • Several participants note that online references do not indicate a dependency of atomic radius on isotopes and emphasize that atomic radius is primarily influenced by Coulomb forces, with neutrons playing no role.
  • One participant counters that scientific encyclopedias indicate isotopes of an element have different radii, although the differences are described as small and lacking specific examples.
  • There is mention of a specific reference, "Table of Isotopes" by Rb Firestone, which may contain relevant data on isotope radii, but access to this resource is limited.

Areas of Agreement / Disagreement

Participants express differing views on whether isotopes affect atomic radii, with some asserting that they do not while others reference sources that suggest they do. The discussion remains unresolved, with no consensus on the relationship between isotopes and atomic radii.

Contextual Notes

Participants highlight limitations in available literature, including a lack of definitive references and varying definitions of atomic radius. The discussion reflects uncertainty regarding the influence of isotopes on atomic radii and the clarity of existing data.

elas
Apologies for raising this question again, but it has finally dawned on me that as the Tables of Elements give an average mass (i.e. for all isotopes of each element) as the Relative Atomic Mass for that element; then my question is -
Is the figure quoted for Atomic Radii also an average figure?

Note that none of the tables actually say that the radius is an average, I just wonder if I am suppose to make that connection myself. Given that the two measurements are always in different sections of the tables it seems to show a lack of clarity on the part of the authors.
 
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Educated guess: Atomic radii are essentially defined by the electronic structure of the atom. Different isotopes of the same element have the same number of electrons, so I strongly suspect that they have the same radius. The radius of the nucleus is very small compared to that of the atom, so the difference in the number of neutrons shouldn't have any effect.
 
mathman
This was the reply to an earlier question but Mcgraw-Hills Encyclopedia of Science and several lesser encyclopedias dissagree; they say there is a difference but do not quote any figures.
There seems to be a lack of clarity on this data.
 
The only book that might contain the atomic radii of isotopes is "Table of Isotopes" by Rb Firestone published by John Wiley and Sons Inc.
The only copy I have traced is in the British Library-reference section. To far to travel and too expensive to buy. If anyone has access to a copy please let me know what it contains appertaining to isotope radii.
 
Originally posted by elas
mathman
This was the reply to an earlier question but Mcgraw-Hills Encyclopedia of Science and several lesser encyclopedias dissagree; they say there is a difference but do not quote any figures.
There seems to be a lack of clarity on this data.

May I suggest research in Rydberg atoms. That is atoms in their almost largest excited state with the outermost electron in a high energy level. Note that they can be a much as 100,000 times larger than normal atoms. Case in point: Rydberg atoms acting like hydrogen with n=400 would have a diameter of 10um where as a normal hydrogen diameter is only 1.1*10^-4um.
 
Using the google search engine for "atomic radius", I found may references with data and descriptions. In all cases, there was no indication of dependency on isotope. Moreover, in describing what the radius means (there were several different definitions, with different numbers), it was always a result of Coloumb forces, where neutrons have no role.
 
Originally posted by mathman
Using the google search engine for "atomic radius", I found may references with data and descriptions. In all cases, there was no indication of dependency on isotope. Moreover, in describing what the radius means (there were several different definitions, with different numbers), it was always a result of Coloumb forces, where neutrons have no role.

That's true and I think he is missing the point that the nucleus doesn't really have anything to do with the radius of an atom because of how electrons act in the cloud.
 
You are correct in respect of the information available on the net but wrong in your comment on atoms.
I have checked three scientific enclopedias on sale at present (i.e. latest editions) and the one in the reference section of the local library. They all state that isotopes of a given element have different radii (two comment on the smallness of the difference) but none gives a table or example.
As mention previously, the only solution as to whether or not the measurements are known is probably in Firestones 'Table of Elements'. Earlier editions were written by E Browne.
One encyclopedia does explain why electrons are not wholly responsible for atomic radii, but I could not memorise the details.
The lack of a definite or authoritive reference on this point leads me to conclude that there is no known answer at present.
 
Please go to Vacuum force model in "theory Developement"
 

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