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SiH4 and CH4
The only intermolecular force they both have is London Dispersion forces
Strength of LDF is determined by molar mass
molar mass of SiH4 = 32.132
molar mass of CH4 = 48.42
Therefore shouldn't CH4 have a stronger LDF??
The answer says that SiH4 has a greater intermolecular force...why is that?
Look at the boiling points. Interaction is based on geometry (surface area) and polarizability, among other things - and the phase: solid, liquid, vapor. Molecular weight is not diagnostic. SiH4 is "fluffy" versus methane being "hard." Compare the melting and boiling points of decane and isodecane versus adamantane, all being $\ce{C_{10}}$. Compare the melting and boiling points of n-octane versus 2,2,3,3-tetramethylbutane, both $\ce{C8H_{18}}$. Complicated.
You might check your MW for methane. Bells and whistles should have gone off, $\ce{CH4}$ versus $\ce{SiH4}$.
The molar mass of SiH4 is ~32, however the molar mass of CH4 is ~16. This explains the textbook's answer. Uncle Al, however, provides a more detailed answer.
