Monolayers and Avogadro's Number
The determination of the size of a molecule or atom is entertwined with the determination of Avogadro's Number, the number of molecules in one mole of a substance.
Along the way to ever better determinations of NA, monomolecular layers of oil played a major role.
If all one wants to do is estimate the size of a molecule of oil, there is no need to reference Avogadro's Number (NA). However, pushing the analysis all the way to evaluate NA, then cross checking this value against other estimates, will act as confirmation that the layer is really monomolecular.
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