Why does magnesium burn with a white flame? What does it say about the electron transitions that take place?

The reaction of Mg with oxygen of the air produces heat. It takes more energy to produce white light than red light.

Does it mean it's moving to a much lower shell?

Yes. When a reaction gives off heat it is said to be exothermic and the enthalpy of the reaction is negative.

Magnesium burns with a white flame due to a phenomenon called incandescence. When a substance burns, it undergoes a chemical reaction known as combustion, releasing energy in the form of light and heat. In the case of magnesium, the high temperature during combustion causes it to emit white light.

To understand the electron transitions that occur during magnesium combustion, let's consider the electronic structure of magnesium. Magnesium has 12 electrons, arranged in energy levels or shells around the nucleus. The first 2 electrons occupy the innermost shell, while the remaining 10 electrons are distributed in the second and third energy levels.

When magnesium is heated and reaches its ignition temperature, the outermost electrons in the third energy level gain enough energy to jump to higher energy levels. These excited electrons are in an unstable state and quickly fall back to their original energy level, releasing the excess energy in the form of light. This light emission covers a broad range of wavelengths, resulting in the perception of a white flame.

The phenomenon of incandescence and the color of the flame provide information about the specific energy transitions taking place. In this case, the white color indicates that multiple energy level transitions occur simultaneously, resulting in a combination of different wavelengths of light. This suggests that the energy levels in magnesium are closely spaced, allowing for a wide range of electronic transitions and emission of light across the visible spectrum.

In summary, the white flame produced by burning magnesium is a result of incandescence caused by the release of excess energy from excited electrons during combustion. The broad range of electron transitions taking place in magnesium accounts for the perception of a white color.