Question

classify the species given below by the intermolecular forces present in a pure sample of each:

Ar H2 HCN HF BrCl5 NH3 CH3OH H2S PF5 CH2Cl2

are they dispersion, dipole-dipole, or h bond?

Answer 1

Concepts and reason

Determine the types of intermolecular forces amongst the molecule.

Fundamentals

When a molecule is present along with similar or dissimilar molecules in close vicinity they are under the influence of intermolecular forces. These intermolecular forces can be repulsive or attractive in nature based on the distance between them and the type of molecules.

The given forces are defined as follows:

Ion-dipole: It is an attractive force experienced by an ion and of opposite polarity which arises when it is present in close proximity of a dipole.

Hydrogen bonding: It is an attractive force that exist between the molecules which have hydrogen atom bonded to an electronegative atom.

Dipole-dipole: It is an attractive force experienced by two dipoles of opposite polarity which arises when they are present in close proximity.

London dispersion: The London dispersion force is a temporary attractive force that arise from electrons present at two adjacent atoms making temporary dipoles.

This force is sometimes called an induced dipole-induced dipole attraction or London forces.

This force is majorly present in the symmetrical non-polar molecules.

The London dispersion force is the weakest intermolecular force.

Covalent forces: Covalent bond is formed by the sharing of electrons between atoms. There is very less electronegativity difference between the constituent atoms. The forces present in these molecules are called covalent forces.

Metallic forces: These types of forces are present in metallic solids.

Consider the following molecules:

${{\rm{H}}_{\rm{2}}}{\rm{, Ar, HCN, BrC}}{{\rm{l}}_{\rm{5}}}{\rm{, HF, N}}{{\rm{H}}_3}{\rm{, C}}{{\rm{H}}_3}{\rm{OH, }}{{\rm{H}}_2}{\rm{S, P}}{{\rm{F}}_5}{\rm{, C}}{{\rm{H}}_2}{\rm{C}}{{\rm{l}}_2}$

Molecules having solely dispersion forces as the intermolecular forces are as follows:

${{\rm{H}}_{\rm{2}}}{\rm{, Ar, and P}}{{\rm{F}}_5}$

Dispersion forces are present in every kind of molecules, therefore almost all the molecule have dispersion forces in them.

Molecule having hydrogen bonding solely as their intermolecular forces are as follows:

${\rm{HF, N}}{{\rm{H}}_3}{\rm{,}}\,{\rm{C}}{{\rm{H}}_3}{\rm{OH}}$

The molecule having dipole-dipole forces are as follows:

${\rm{HCN,BrC}}{{\rm{l}}_{\rm{5}}}{\rm{,}}\,{{\rm{H}}_2}{\rm{S,}}\,{\rm{and C}}{{\rm{H}}_2}{\rm{C}}{{\rm{l}}_2}$

Ans:

Molecules having solely dispersion forces as the intermolecular forces are as follows:

${{\rm{H}}_{\rm{2}}}{\rm{, Ar, and P}}{{\rm{F}}_5}$

Molecule having hydrogen bonding solely as their intermolecular forces are as follows:

${\rm{HF, N}}{{\rm{H}}_3}{\rm{,}}\,{\rm{C}}{{\rm{H}}_3}{\rm{OH}}$

The molecule having dipole-dipole forces are as follows:

${\rm{HCN,BrC}}{{\rm{l}}_{\rm{5}}}{\rm{,}}\,{{\rm{H}}_2}{\rm{S,}}\,{\rm{and C}}{{\rm{H}}_2}{\rm{C}}{{\rm{l}}_2}$