What are Vander Waal's Radii?

Vander Waal's radii can be assigned to the atoms of molecules on the basis of the closeness of approach of these atoms in crystalline substances. 

Diffraction studies of crystals give information about hoe molecules can approach each other and can pack together. Forces, often treated under the name vander Waal's forces, provide the attraction and repulsion between molecules that are responsible for the closeness with which molecules can approach other. The idea of a vander Waals radius for each covalently bound atom is introduced. The shapes attributed to molecules as a result of the introduction of vander Waals radii.

The values of these radii can be deduced from the distances that separate atoms in different molecules in a crystal lattice. In crystalline Br2, the shortest distance between a bromine atom of one molecule and that of an adjacent molecule is 390 pm. Half this value, 195 pm, can therefore be assigned as the van der Waals radius of a covalently bound bromine atom. In similar ways, by making use of crystal structure data for many organic compounds, the van der Waals radii can be deduced. These values must be considered reliable to not more than about 5 pm, and this uncertainty makes itself evident in the range of values found for a particular element in different compounds and crystals. The values are sufficiently reliable, however, for scale drawings to be constructed and used to see hoe molecules can fit together. That van der Waals radii can be assigned with some success is attributable to the fact, mentioned, that the repulsive forces set in very strongly i.e. the potential energy curve raised very steeply, as atoms approach each other. It follows that even when rather different attractive forces operate, the closeness of approach is affected little.

2125_Vander waals.png

   Related Questions in Chemistry

  • Q : Calculating density of water using

    What is the percent error in calculating the density of water using the ideal gas law for the following conditions:  a. 110 oC, 1 bar   b. 210 oC 10 bar  c. 374 o

  • Q : Vapour pressure of a liquid Help me to

    Help me to go through this problem. The vapour pressure of a liquid depends on: (a) Temperature but not on volume (b) Volume but not on temperature (c) Temperature and volume (d) Neither on temperature nor on volume

  • Q : Chem Silicon has three naturally

    Silicon has three naturally occurring isotopes. 28Si, mass = 27.976927; 29Si, mass = 28.976495; 30Si, mass = 29.973770 and 3.10% abundance. What is the abundance of 28Si?

  • Q : What is synthetic rubber and how it

    To meet human needs, scientists have started preparing synthetic rubbers. Besides having similar properties as natural rubbers they are tougher, more flexible and more durable than natural rubber. They are capable of getting stretched to twice its length. Though, it reverts to its original shape

  • Q : Problem on melting of ice A) It has

    A) It has been suggested that the surface melting of ice plays a role in enabling speed skaters to achieve peak performance. Carry out the following calculation to test this hypothesis. Suppose that the width of the skate in contact with the ice has been reduced by sh

  • Q : Explain the process of adsorption of

    The extent of adsorption of a gas on a solid adsorbent is affected by the following factors: 1. Nature of the gas Since physical adsorption is non-specific in nature, every gas will get adsorbed on the

  • Q : Preparation of normal solution Give me

    Give me answer of this question. What weight of ferrous ammonium sulphate is requiored to prepare 100 ml of 0.1 normal solution (mol. wt. 392): (a) 39.2 gm (b) 3.92 gm (c)1.96 gm (d)19.6 gm

  • Q : Electrons present in a benzene How

    How many electrons are present in a benzene?

  • Q : Problem on decinormal strength Can

    Can someone please help me in getting through this problem. How many grams of dibasic acid (having mol. wt. 200) must be present in 100ml  of its aqueous solution to provide decinormal strength: (i) 1g  (ii)2g  (iii) 10g  (iv) 20g<

  • Q : Organic and inorganic chemistry Write

    Write down a short note on the differences between the organic and inorganic chemistry?

©TutorsGlobe All rights reserved 2022-2023.