Talk:Van der Waals radius

message: I'm not a chemist (still in high-school), but shouldn't this read PV = nRT? :-\ /splintax
:You are right and wrong! I think the original author intended V to equal the molar volume but due to the limitations of the font used here, the "~" couldn't be placed over the V. In practice you try to use equimolar volumes in your calculations. I'll try and place a link to the actual equation.
:Also, I don't want to confuse my high-school friend but, there should be something said about polarizability volumes and van der Waals. I can remember right now what the connection is (there may not be any) but I'll look over my notes from college.
afn
::Yes, there should be something said about that! I'm working on it, slowly... Physchim62 (talk) 15:31, 27 April 2007 (UTC)
thread_title: pV=nRT

message: When a word is quoted in a definition, it is a signal, first, that the reader should not take the meaning of the quoted word literally, and second, that the author already has or soon will clarify what is meant by the quoted term.  
Unfortunately, the author never did explain why he was not satisfied with the word "occupied" when referring to the volumetric space taken up by a molecule at a given position.  If the word is not "occupied", then what word is it?
This may appear to be a minor quibble, but it is far from it:  this entire article is ABOUT measuring the space taken up by a molecule -- and that figures quite fundamentally in our understanding of the natural world.  The author may believe he is in possession of an inexpressible subtlety of molecular mechanics, and is using the quoted word to signal such priestly knowledge.  If so, forget it!  Wikipedia/Chemistry is all about elegantly expressing the what is known and unknown about our material world, so that the common man may better appreciate its majesty and order.  
Inquiring minds, including but not limited to my own, want to know:  does a molecule occupy space or not?  There is a suggestion here to the contrary, and I find that profoundly disturbing. Contrablue (talk) 02:15, 10 February 2011 (UTC)
thread_title: Space "occupied" by a molecule

message: How does one find this radius, is there an equation to find it? The equation on this page doesn't seem to have the "radius" as a variable. Fresheneesz 03:19, 1 June 2006 (UTC)
thread_title: Radius

message: I'm not a chemical scientist, in fact, I am far from being one, so correct me if I am wrong. I noticed the values for some of the chemicals listed on the right on the top of the page seem a little wrong. In one of the papers I am using, most of the VDW radii are identical, except Fluorine (F), Phosphorus (P), Sulfur (S), and Chlorine (Cl), and I don't have the value for copper. I then checked up on the individual pages for all the listed chemicals, and realised the radii listed on those pages are the same as mine (except copper, which is missing from my records). On the individual pages, F has a radius of 1.47 A compared to the listed 1.35, 1.80 compared to 1.9 for P, 1.80 compared to 1.85 for S, and 1.75 compared to 1.8 for Cl. Can the maintainer of the page please correct them. Thanks! Wpliao (talk) 04:21, 31 July 2008 (UTC)
replies: text: There is no "maintainer" to the page - it's a wiki and anyone can edit!. The ideal person to update this would be you, as you already looked up those values in textbooks ans so can also cite where the values are coming from! (that is better than just copying them from the other pages as you can put a citation in and the data becomes verifyable) Iridos (talk) 23:26, 23 September 2008 (UTC)
replies: text:  I changed them - you can still double-check my edit and perhaps put your source in (I just compared to the articles and to the web-page given in this article) - if you looked the values up in a textbook and they are correct, please put  your textbook citation  on top of the table (if your literature covers all values) Iridos (talk) 23:38, 23 September 2008 (UTC)

text: I've checked the original source of these values (the Bondi paper now cited in the article) and the table is OK. As the article now points out, there are other values out there, although I think Bondi's are the most widely used. Physchim62 (talk) 20:27, 24 September 2008 (UTC)
thread_title: Incorrect Radii?

message: There doesn't appear to be a formal definition of the van der Waal's radius here. The introduction states that they can be used to model physical properties of atoms and molecules, but then goes on to talk about the van der Waal's volume and never gives a formal definition.  —Preceding unsigned comment added by Joshdkatz (talk • contribs) 23:22, 16 September 2009 (UTC)
thread_title:  Definition 

message: http://www.ncbi.nlm.nih.gov/pubmed/12968888
Abstract
:The van der Waals volume is a widely used descriptor in modeling physicochemical properties. However, the calculation of the van der Waals volume (V(vdW)) is rather time-consuming, from Bondi group contributions, for a large data set. A new method for calculating van der Waals volume has been developed, based on Bondi radii. The method, termed Atomic and Bond Contributions of van der Waals volume (VABC), is very simple and fast. The only information needed for calculating VABC is atomic contributions and the number of atoms, bonds, and rings. Then, the van der Waals volume (A(3)/molecule) can be calculated from the following formula: V(vdW) = summation operator all atom contributions - 5.92N(B) - 14.7R(A) - 3.8R(NR) (N(B) is the number of bonds, R(A) is the number of aromatic rings, and R(NA) is the number of nonaromatic rings). The number of bonds present (N(B)) can be simply calculated by N(B) = N - 1 + R(A) + R(NA) (where N is the total number of atoms). A simple Excel spread sheet has been made to calculate van der Waals volumes for a wide range of 677 organic compounds, including 237 drug compounds. The results show that the van der Waals volumes calculated from VABC are equivalent to the computer-calculated van der Waals volumes for organic compounds.
Just granpa (talk) 14:24, 20 November 2010 (UTC)
thread_title:  Fast calculation of van der Waals volume as a sum of atomic and bond contributions 

message: I read in the present article: "For helium, b = 23.7 cm3/mol. Helium is a monatomic gas, and each mole of helium contains 6.022×1023 atoms... Therefore the van der Waals volume of a single atom Vw = 39.36 Å3, which corresponds to rw = 2.11 Å."
A 4x factor seems to be missing from the equation: another article (https://en.wikipedia.org/wiki/Van_der_Waals_equation#Conventional_derivation) states that "The excluded volume b is not just equal to the volume occupied by the solid, finite-sized particles, but actually four times that volume" and goes on explaining why.
After dividing b by four, I find rw = 1.33 Å, which is closer to the Van der Waals radius found in other sources (1.40 Å), for example http://www.webelements.com/helium/atom_sizes.html
Can somebody a bit more experienced than me look into that? Cvereb (talk) 23:54, 13 December 2014 (UTC)
thread_title:  Van der Waals volume vs radius 

message: :Template:Atomic radii
Just granpa (talk) 10:15, 10 August 2017 (UTC)
thread_title:  New template 

message: Space
 Pushpa R Waghmare (talk) 16:54, 14 November 2017 (UTC)
thread_title:  Astronomy