 You can see the fingerprint photon emissions of some elements if you carry out a flame test in the lab or You can set off some fireworks Flame tests can be used to determine the identity of metal ions in a solution or a solid Lunch-leave chemistry is going to explain how this works When we view salts we tend to visualize cat ions and anions floating around in solution along with the water of course However, identifying unknown cat ions in aqueous solutions tends to be problematic as colorless in solution with the exception of iron 2, iron 3 and copper ions If these solutions are put through a flame test many metal cat ions produce Characteristic colors when they're subjected to a blue bunsen flame Just think about fireworks Anyways, the reason for this lies in the electron shell structure of the atom When a metal salt is vaporized in a flame The outer shell electrons of the metal ion may absorb energy and move to a higher excited energy level Excited electrons iron sable and as they fall back to low levels they emit light on various characteristic frequencies Some of these frequencies correspond to the visible region of the electromagnetic spectrum We see the result of the emission of these colored photons In fact the color emitted by the larger atoms is lower in energy and the light emitted by smaller ions So for example strontium atomic number 38 gives a reddish color as compared to the yellow color of sodium atomic number 11 The sodium ion is greater affinity for the valence electron So more energy is required to move that electron When it does move it goes to a higher excited state as the electron descends to the ground state It has more energy to disperse which means the color has a higher frequency slash shorter wavelength But what about the anion you ask? Well, we generally use chloride salts in which chlorides valence electrons are strongly held to the nucleus because of the high electron negativity It is possible to excite these valence electrons But as it is in fact to the ground state the emission spectrum is generally outside our visible range So don't contribute to the flame color You