Why do different elements burn different colours in flame tests?

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Like potassium burning lilac etc

In: Chemistry

It’s to do with the number of electrons in the outer shell of the atoms, how much energy they absorb and give back when they burn, and the wavelength and frequency of the energy emitted in doing so.

Electrons in an atoms have specific amounts of energy. It’s like a ladder where the space between each rung on the ladder is based off of how many protons are in the nucleus (it’s actually some quantum mechanics, but that’s well above eli5).

When you burn them, the energy in the chemical reaction can cause electrons to jump up to a higher rung, as long as it isn’t already full of other electrons. After they jump up they fall back to where they started almost immediately, and release that energy from falling as light. The color of the light depends on how far the electron fell. A big fall means blue or purple light. A small fall means red light, or sometimes they go further in either direction (ultraviolet, infrared, microwave, etc). So since different elements have different energy ladders, they release different colors of light when they burn.