Question

Boiling point of hydrogen fluoride is highest amongst HF, HCl, HBr and HI. Which types of intermolecular forces are present in hydrogen fluoride?
A.)H-F has highest Vander Waals forces and dipole moment
B.)H-F has highest London forces
C.)H-F has highest dipole moment and has dipole-dipole, London forces and hydrogen bonding
D.)H-F has strong intermolecular interactions like dipole-induced dipole

Answer 1

Hint: All the halogens belong to the 7th group in the periodic table. As we are moving from top to bottom in the periodic table the electronegativity of the atoms decreases and size of the atom increases.
The London force is the weakest intermolecular force present in few molecules. The London force is temporary attractive forces that happen when the electrons in two adjacent atoms in a molecule occupy positions that make the atoms and form temporary dipoles. This London force is sometimes called as induced dipole-induced dipole attraction.

Complete step by step answer:
The dipole moment is nothing but the change in the bond length in between atoms of a molecule.
The dipole moment is high in case of hydro halogens due to the high electronegativity of halogens.
As we know that electronegativity of the halogens decreases as we from top to bottom in the periodic table. As the electronegativity of the atoms decreases the dipole moment of the halogen atoms also decreases.
Hydrogen bonding is a superior type of dipole-dipole attraction between molecules. It is not a covalent bond with a hydrogen atom.
We know that hydrogen bonding occurs from the attractive force between hydrogen atoms covalently bonded to very high electronegative atoms like Nitrogen, Oxygen or Fluorine atoms.
Now coming to the given option C, H-F has the highest dipole moment and has dipole-dipole, London forces and hydrogen bonding.
Yes option C is correct because H-F has high dipole moment, has dipole-dipole, and shows London forces and hydrogen bonding when compared to remaining HCl, HBr and HI. Because of all the forces hydrogen fluoride shows the highest boiling point.
Hence, the correct answer is option C.

Note:
Boiling point of all hydrogen halides is high, but the boiling point of hydrogen fluoride is high when compared to the remaining hydrogen halides due to the above mentioned reasons.