Understanding Atomic Radii: Average Figures or Unclear Measurement?

In summary, the question being raised is whether the figure quoted for Atomic Radii is an average or not, given that the Tables of Elements do not explicitly state it. The educated guess is that isotopes of the same element have the same radius, as the radius is determined by the electronic structure of the atom. However, some sources disagree and state that there is a difference in radii between isotopes, but do not provide any specific figures or data. Further research is suggested in Rydberg atoms, which have a much larger radius due to their high energy levels. While there is information available on the internet, it seems that there is a lack of clarity and agreement on this topic, and the only
  • #1
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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  • #2
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.
 
  • #3
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but Mcgraw-Hills Encyclopedia of Science and several lesser encyclopedias dissagree; they say there is a difference but do not quote any figures.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.
 
  • #4
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.
 
  • #5
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.
 
  • #6
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.
 
  • #7
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.
 
  • #8
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.
 
  • #9
Please go to Vacuum force model in "theory Developement"
 

1. What is atomic radius and why is it important?

Atomic radius is the distance from the center of an atom's nucleus to its outermost electron. It is an important concept in chemistry as it helps us understand the size of atoms and how they interact with each other. Atomic radius also affects properties such as ionization energy, electronegativity, and chemical reactivity.

2. How is atomic radius measured?

Atomic radius is usually measured in picometers (pm) or angstroms (Å). The most common method of measurement is using X-ray crystallography, where the distance between atoms in a crystal lattice is measured. Other methods include spectroscopy and electron microscopy.

3. Are average atomic radii figures accurate?

Average atomic radii figures are based on theoretical calculations and are not always accurate. This is because the size of an atom can vary depending on its state (solid, liquid, or gas) and its chemical environment. Additionally, the presence of electron clouds and different electron configurations can also affect atomic radius measurements.

4. How do atomic radii change across the periodic table?

Generally, atomic radii decrease from left to right across a period in the periodic table due to an increase in the number of protons and electrons, which leads to a stronger attraction between the nucleus and electrons. However, atomic radii increase down a group due to the addition of new energy levels and the shielding effect of inner electrons.

5. Can atomic radii be compared between different elements?

It is not accurate to compare atomic radii between different elements, as each element has a unique atomic structure and properties that affect its atomic radius. Additionally, different measurement methods and experimental conditions can also lead to variations in atomic radius values.

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