Name: Graham's Diffusion Law
Uploaded: 2019-07-19
Duration: 9 min 43 s
Description: Gases diffuse at a different rate. Watch this video to understand Graham's diffusion law, which deals with the diffusion of gases. Have fun learning!

Question

Name the different intermolecular forces experienced by the molecules of a gas.

Accepted Answer

The attractive or repulsive forces that exist between interacting particles (i.e. atoms or molecules) are called intermolecular forces. Since, the existence of these attractive forces was first shown by Dutch scientist Johannes van der Waals’, so these forces are also known as van der Waals’ forces. The different types of van der Waals’ forces are given below:

(i) Dispersion forces or London forces: In neutral atoms and non-polar molecules, the electron cloud is symmetrically distributed hence, they do not have polarity. Even in such cases, symmetry in electron cloud may be lost momentarily producing instantaneous or transient dipole. This distorts the electron cloud of the neighbouring atom or non-polar molecule inducing a dipole. The attraction between these instantaneous dipoles are called dispersion forces or London forces. Example: Dispersion forces between $Ar$ atoms, $H_{2}$ molecules, etc.

(ii) Dipole-Dipole forces: These forces exist between the molecules having permanent dipoles like $HCl, {NH}_{3}$ , etc. These forces arise because of the interaction between oppositely charged ends, i.e., positive end of one molecule attracts the negative end of the other molecule and vice-versa.

(iii) Dipole-Induced dipole forces: These forces exist between the polar molecules having permanent dipole and non-polar molecules lacking dipole. As the charged end of the polar molecule induces dipole in the non-polar molecule by deforming its electron cloud and hence, both the molecules get attracted by dipole-induced dipole forces. Example: Attractive forces between $HCl$ and ${CCl}_{4}$ molecules.

(iv) Ion-dipole interaction: The force of attraction existing between an ion (cation or anion) and a dipole is called ion-dipole forces. Example: when sodium chloride is dissolved in water, it gets split up into ${Na}^{+}$ and ${Cl}^{-}$ ions.
These ions get surrounded by water molecules which have a dipole moment. Due to hydration of the ions, the water molecules act as a dielectric to keep the ions separated and therefore, $NaCl$ dissolves in water.

(v) Repulsive forces: These forces exist between the electron clouds or the nuclei of two molecules when they are in contact with each other.

(vi) Hydrogen bond: It is a special case of dipole-dipole interaction, and is formed (or such force exists) when a hydrogen is bonded to a more electronegative atom (like, $N, O$ or $F$ ). Example: Hydrogen bonding between water molecules, hydrogen fluoride molecules, etc.

(vii) Metallic bonding: The peculiar type of bonding which holds the metal atoms together in a metal crystal is called metallic bonding.

Name the different intermolecular forces experienced by the molecules of a gas.

Important Questions on States of Matter : Gases and Liquids

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