Visible Spectra of the Elements
If the emission lines of the chemical elements were observed through a diffraction grating, they would probably look something like this:
Periodic table format
This image is based on spectrum line positions and intensities from MIT Wavelength Tables and the NIST Atomic Spectrum Database. A few spectra (neon, for instance) have had corrections applied in order to more closely match my own personal observations.
Astatine is missing from this image as I have no visible wavelength data to go on. Only one line is shown for francium as that is also the only datum available.
Disclaimer: I personally have not had opportunity to observe all elements, especially those which are expensive, hard to find, or radioactive. Therefore, some spectra may deviate considerably from the depictions pictured here. Elements which I have observed in a semi pure state include: hydrogen, helium, nitrogen, neon, sodium, magnesium, aluminum, argon, iron, nickel, copper, zinc, silver, cadmium, tin, xenon, platinum, and mercury. I can vouch for all of these appearing almost exactly as depicted. Elements I have seen in mixtures with other elements include scandium, krypton, molybdenum, and lead. I am reasonably sure that all of these appear more or less as depicted.