Explain Instantaneous Dipole-induced Dipole Forces Or London Dispersion Forces?


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Muhammad Azhar answered
The momentary forces of attraction that exist between instantaneous dipole and induced dipole are called instantaneous dipole-induced dipole forces or London Dispersion forces.
Explanation: These forces are created among the non polar molecules like He. Ne, Ar, Fb, Ch, CH4, which have no dipoles at normal conditions. London forces are responsible for the liquefaction of above gases. A German physicist Fritz London in 1930 explained the creation of these forces in non-polar molecules.

Examples: Consider creation of London forces in mono atomic molecules of Helium. When 'He' atoms come close to each other, their electrons repel. The electrons density of atoms becomes unsymmetrical. A temporary dipole called instantaneous dipole is created on the He atom. This momentary dipole then disturb the electronic cloud density of its neighboring He atoms, producing an induced dipole or polarity. All these polar atoms attract each other. There forces of attraction which are present between instantaneous dipole and induced dipole are called London dispersion forces. These forces are found in all types of molecules either polar or non-polar.These forces are very important in non-polar molecules. These are very short-lived attractive forces. The reason is that electrons keep on moving. Due to electronic movement, the dipoles vanish as quickly as they are formed. A moment later they again appear in a different orientation and again weak London forces are created.

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