# chemistry help

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our teacher said on our final chemistry lab test there will be a question asking us to convert nanometers to wave numbers, anyone know what the question might be phrased like? also, im not sure i know how to convert, anyone have an example question with the steps?

• chemistry help -

A wavelength, for example 5 nm, is converted to wave numbers by first converting nm to m then taking the reciprocal.
5 nm = 5E-9 m and (1/5E-9 m) = 2E8 reciprocal meters or 2E9 m^-1.
In practice, we can have reciprocal centimeters (for wavelengths in cm), reciprocal meters (for wavelengths in m), reciprocal nm (for wavelengths in nm) etc. In the old literature, wave number in cm^-1 (reciprocal centimeters) was called kayser or inverse centimeters. I haven't seen the kayser term used in years. I think whether you convert nm to m or to some other unit first (or don't convert at all) before taking the reciprocal is a matter of preference.

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