What is vandar walls forces वानडर वाल्स फोर्स क्या है

What is vandar walls forces

The force of attraction exiting among the molecules offer substance (gaseous liquid or solid) are called Vander walls forces or intermolecular forces. These forces are of three different types as explained below.

1. Dipole dipole interaction

These forces are found in polar molecules having permanent polarity In them. A polar molecule has separated centre of positive and negative charge and passes permanent polar moment when polar molecules are brought nearer to each other le they oriente themselves in such a way that the positive end of one dipole attract the negative and of another dipole and vice versa. Dipole- dipole interaction between polar molecules are also called Keesom forces and the strongest all other type of Vander walls forces.

Example: a simple example is that of HCL in which chlorine being more electronegative Aquarius is slightly positive charge.

  

   $ +        $-          $+          $ -

   H------Cl.           H--------Cl

          ↘️            ↙️

        Dipole-dipole attraction

2.Dipole induced dipole interaction

These forces exist between polar (H+____F-) and iron polar molecules (eg. H2,O2 etc). The positive end of polar molecule attracts the mobile electron cloud of the nun polar molecule to word itself.

3. temporarily dipole induced dipole Interactions or London forces

These forces are found in nonpolar molecules such as diatomic ok gases like H2,O2,Cl2,N2 etc.as well as mono atomic noble gases like He,Ne,Ar,etc 

In an polar atom or molecule has a positive centre and electron cloud move around it Symmetrycally. The atoms are attracted to each other due to the mild electronic force of attraction between instant aneus  dipole and induced dipole.These forces are responsible for the condensation of gases.

Characteristics of Vander walls forces

1.  These forces are only short range forces. In the simplest molecules they are important only up to 10th power - 7 cm

2.  These forces are much bigger than covalent and hydrogen bonds. Since Vanderwall forces are easily overcome the condenesd gas readily vaprorises.

Molecules crystal are soft and have low melting points.

Factors affecting the magnitude of Vander walls forces

1. Number of electron present in molecule

        The magnitude of Vander walls forces increases with the number of electrons in the molecule. With the increase in wonder was forces in the boiling point of the molecule also increase .

2. Molecular mass

      Higher the molecular mass of a molecule the stronger is the Vander walls force and hence boiling point increase .    

What is the pi Bond 

 Pi bonds are formed by the side wise positive overlap of atomic orbitals along a direction perpendicular to the internuclear exis .During the formation of Pi bonds in the axis of the atomic orbitals are parallel to the other where as the overlapping is per  pendicular to the internuclear is illustrated below.