X-Ray Spectra We have seen that hydrogen emission lines come in groups, and that the shortest wavelengths of light it can produce fall in the UV portion of the spectrum. Clearly, x-ray wavelengths would have to come from other atoms. In fact, the Rydberg equation can be adjusted so that it approximates the emission spectra of heavier elements if we divide by the square of the atomic number , Z , which is simply the element’s number on the periodic table: λ = R n n' / ( n – n' ) Z , where the Rydberg wavelength is still 91.1nm . Recognizing that the shortest wavelengths are produced when n'=1 and n= ∞ , it follows that to get a wavelength around 100pm , Z must be at least 20. Transition metals are ideal candidates for this. The caveat to using the modified Rydberg equation is that the atom in question must be missing all but one electron. Otherwise, it is not enough like hydrogen to yield any accuracy. Still, it was found that when metal targets were bombarded by cathode rays—beams of fast electrons—x rays emissions were the result. A notation often employed for specifying spectral emission lines due to electron de-
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