Why do non metallic elements not give off any colour to the flame in a flame test?
The simple answer is that there is simply not enough energy. Because the electrons are more tightly bound to the atoms of a nonmetal (nonmetals tend to have higher effective nuclear charge than metals), you need more energy than a Bunsen burner can supply. Nonmetal elements do have emission lines in the visible range of the spectrum. But to see them, you need more energy to excite the electron s. You can use a high voltage spark (using a discharge lamp filled with nonmetal vapor). Then you will definitely see emission in the visible range. This is basically how “neon” lights work.
