Wavelength and Diameter

[veeksha25]

On one of the practice finals, it asks "Given that the diameter of a helium atom is approximately 10^-10 m; does your answer make sense?" And the answer is "since the wavelength is less than the diameter, yes it makes sense."

I don't remember reading about this, is this a principle and if so why? Also, if the wavelength is greater does it mean it does not make sense?

[Chem_Mod]

Yes it is a general principle. The electron is bound to an atom, therefore the electron's wavelength is less than the size of the atom.
It would be unusual for the electron's wavelength to be bigger than the atom it is bound to. Ask me in my Wed office hours if this is not clear.