In: Chemistry
In each pair, indicate which substance has the stronger intermolecular forces and explain your reasoning: (a) Ne, Ar; (b) NF3, BF3; (c) SiH4, GeH4; (d) NaF, HF.
a) Ar
Ne and Ar have dispersion forces which increases with size and mass. Since, Ar is a larger atom with a greater molecular mass, it would have greater dispersion forces.
b) NF3
NF3 is a polar molecule and has dipole-dipole interactions, along with dispersion forces. Whereas, BF3 is a non-polar molecule(due to its trigonal planar geometry, the dipole moments of the three B-F bonds cancel each other) and has only dispersion forces. Hence, NF3 has stronger intermolecular forces.
c) GeH4
Both SiH4 and GeH4 molecules are non-polar (due to the tetrahedral geometry). They have only dispersion forces. Due to a greater mass, GeH4 has stronger dispersion forces.
d) NaF
NaF is an ionic compound and has ionic forces which are strongest of all intermolecular forces. HF is a polar compound and has hydrogen-bonding.
(Note: Though H-bonding are considered to be strong intermolecular forces; they are not as strong as ionic forces)