Question

The type of intermolecular force existing between the molecules of ${\text{BC}}{{\text{l}}_3}$ is
A.Electrostatic force
B.London force
C.Dipole-dipole interaction
D.Dipole induced dipole interaction

Answer 1

${\text{BC}}{{\text{l}}_3}$ is a nonpolar molecule. Electrostatic force exists between charged ions. All the other options are the type of Van der waal forces of attraction.

Complete step by step answer:
Van der Waals forces are the weak and non directional forces. They have bond energy of less than 8 kilojoules per mole. Strength of the van der waal force depends on ease of distortion of electron clouds. Van der waal force can exist between two non polar molecules, two polar molecules, one polar and one non polar molecule, ion and polar molecule and ion and non polar molecule. Types of van der waal forces are as follow:
Ion - dipole interaction which exists between ion (cation or anion) and polar molecule. It is the strongest of all van der waal forces. For example it exists in between chloride ion and hydrogen chloride.
Dipole - Dipole interaction exists between two polar molecules. It is the second strongest van der waal force. For example it exists between two hydrochloride molecules.
Ion – induced dipole interaction exists between ion and nonpolar molecules. For example it exists between bromide ions and hydrogen molecules.
Dipole – Induced Dipole interaction which exist between one polar and another non polar molecule. For example it exists between polar molecules like hydrogen chloride and non polar molecules like chlorine gas.
Londen forces or dispersion forces exist between two non polar molecules. It is the weakest van der waal force. For example it exists between hydrogen and nitrogen gas.
Intramolecular force exists within the same molecule and intermolecular force exists between two molecules. Van der waal force exists between two entities thus it is an intermolecular force.
${\text{BC}}{{\text{l}}_3}$ molecule is a non polar molecule as its net dipole moment is zero. Hence the van der waal force between molecules of ${\text{BC}}{{\text{l}}_3}$ will be London force or dispersion force.

Thus, the correct option is B.

Note:
Melting and boiling point of noble gas elements or inert gas atoms and halogens increases down the group due to increase in size of atom or molecular weight. More the intermolecular force exists between molecules, the more will be its melting and boiling point.