Van der Waals radius not applicable to most elements?

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Discussion Overview

The discussion revolves around the applicability of the Van der Waals radius to various elements, particularly focusing on why certain elements, like Molybdenum, do not have a listed Van der Waals radius. Participants explore definitions, measurement challenges, and the historical context of Van der Waals radii.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants note that Molybdenum lacks a Van der Waals radius and question why this is the case, suggesting that it may not apply to most elements.
  • One participant proposes that the absence of a Van der Waals radius for certain elements could be due to difficulties in measuring intermolecular distances.
  • Another participant suggests that the Van der Waals radius can be calculated using ab initio software, indicating that elements without calculated values may be less commonly used or too large for current computational methods.
  • A participant references A. Bondi's influential paper from 1964, which established widely accepted Van der Waals radii based on x-ray crystallographic data, noting that different researchers may derive varying values based on their experimental approaches.
  • One participant mentions a potential connection between the Casimir Effect and Van der Waals forces, suggesting it may provide additional insights.

Areas of Agreement / Disagreement

Participants express differing views on the reasons behind the absence of Van der Waals radii for certain elements, with no consensus reached on the underlying causes or implications.

Contextual Notes

There are limitations regarding the definitions and measurement techniques for Van der Waals radii, as well as the dependency on specific computational methods that may not cover all elements.

HappyEngineer
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I was looking at the values for the Van der Waals radius on various elements in wikipedia and noticed that Molybdenum does not have one. I searched a bit and found this site
http://www.webelements.com/periodicity/van_der_waals_radius/
which lists the elements that have a Van der Waals radius. The non-purple ones apparently do not have one.

Why is that? I don't see anything in the definition of the Van der Waals radius on wikipedia which indicates that it doesn't apply to most types of elements.
 
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HappyEngineer said:
I was looking at the values for the Van der Waals radius on various elements in wikipedia and noticed that Molybdenum does not have one. I searched a bit and found this site
http://www.webelements.com/periodicity/van_der_waals_radius/
which lists the elements that have a Van der Waals radius. The non-purple ones apparently do not have one.

Why is that? I don't see anything in the definition of the Van der Waals radius on wikipedia which indicates that it doesn't apply to most types of elements.

Perhaps it is due to the inability to measure the intermolecular distances (for whatever reason, e.g. structure). Not sure though.

CS
 
So you're saying that they're not filled in because it's difficult to measure?
 
From my understanding the simplest way to get the Van der Waals radius is to calculate it using ab initio software. The elements that haven't been calculated then are either not widely used or are too big to have been implemented in the ab initio systems yet. Any element that can form a bond would have to have a Van der Waals radius.
 
Funny this question should come up, seeing as I happen to be researching it. The current standards in van de Waals radii come from the most cited paper in the Journal of Physical Chemistry, written by A. Bondi. They still represent the best general, all-purpose radii if one must write in distances and not calculate, even though it was written in 1964. Bondi used mostly x-ray crystallographic data for the purpose. People who have come up with different values do so from a variety of different perpsectives of what a good experiment is to analyze.

Maybe, if I am successful (probably not the way it is going right now...), the entire Periodic Table will be published!
 
I noticed an article on wiki, under the Casimir Effect at short range distances, being analysed with the effect of Van der Waals' force. This may be of help to you.
 

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