Why do salts burn different colors?
Salts have different flame colors because the ions which they are composed of have different numbers of electrons occupying various energy levels. Some typical colors for salts containing the following elements are:
lithium - fuchsia red
sodium - yellow
potassium - lilac
strontium - red
calcium - orange
copper - green
When salts are heated, electrons occupying the outer energy levels of the atoms gain energy from the heat. Electrons usually remain in the ground state, which means that they are in orbitals that are closer to the nucleus and therefore lower in energy. When they absorb energy they move to higher energy levels farther from the nucleus. They are unstable in these higher levels so they fall back, giving off the energy they absorbed in the form of visible light. The color of light emitted corresponds to the energy given off by the electrons, based on how far they move from the nucleus. There are lots of possible energy changes therefore there is a variety of colors depending on the elements.