Question

Which of the following substances has the weakest intermolecular forces? PICK ONE.

A

H2O

B

CH2F2

C

NF3

D

SiH4

E

CH3F

Answer 1

H2O has hydrogen atom attached to oxygen which is one of the most electronegative atoms and thus this molecule shows H-bonding.

CH2F2 molecule is a polar molecule due to the electronegativity difference between carbon and fluorine atoms. Thus it shows dipole-dipole interaction.

NF3 is also polar due to the electronegativity difference between nitrogen and fluorine atoms. Thus it shows dipole-dipole interaction.

SiH4 is not a polar molecule and thus only have very weak intermolecular forces know as london dispersion forces arising due to temporary dipoles created by electrons of one molecule with the other.

CH3F is a polar molecule due to the electronegativity difference between carbonand fluorine atoms. Thus it shows dipole-dipole interaction.

The strength of intermolecular forces follow this order-

H-Bonding > dipole-dipole > london dispersion forces

So, SiH4 has the weakest intermolecular forces.