Chemistry

Why does burning magnesium produce white light, and copper green light?

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Why is that when magnesium is burnt with oxygen on a Bunsen burner it produces and white light (spark) and copper produces a green light? – Sarah

When certain metals (or compounds containing these metals) are heated in a flame, they will make the flame change colour. The colour which is produced, is specific for the metal which is being heated. Copper produces green, Sodium orange, Lithium red. These properties are being used in producing the wonderful colours seen in fireworks.

But how does it work?

To explain this we have to look at the way the metal atoms are made up. Put simply, each atom consists of a nucleus, which is surrounded by ‘clouds’ of electrons.

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The electron clouds exist at discrete energy levels called orbitals. When energy is added to the atoms in the form of heat, the electrons can move up from one orbital to the next by absorbing exactly the energy difference between the orbitals. When they subsequently return to their ground state, the energy they have taken up as heat is emitted in the form of light. Because for each metal the number of electrons and their distribution over the orbitals is unique, its atoms will absorb/release energy in a unique pattern, and the wavelength of the resulting light (in visible light, its colour) is specific for the metal in question.