Why flares and flashbulbs burn so bright

What you notice

Magnesium burns with a dazzling white light that is painful to look at directly. Emergency flares, the brightest white fireworks and early camera flashes used magnesium or magnesium–aluminium alloys for this reason. Many sparklers use aluminium or iron filings instead, but the chemistry is similar: a metal combining with oxygen very quickly. A magnesium flame is hotter than 3000 °C, so hot that the white MgO smoke itself glows and gives off light across the whole visible spectrum. Once lit, magnesium is hard to put out; it even keeps burning in carbon dioxide and steam.

Safety: Do not stare at burning magnesium, and never use water on it, which can make it burn more violently.

Step by step

1. 1

   Getting started

   Solid magnesium is protected by a thin oxide layer, so it must be heated strongly before it ignites. Ribbon and powder catch more easily because of their larger surface area.

2. 2

   Electron transfer

   Each Mg atom gives two electrons to oxygen, becoming Mg2+; each O atom gains two electrons to become O2–.

3. 3

   An ionic lattice forms

   The small, highly charged ions pack into a rock-salt lattice with a very large lattice enthalpy, which is why the reaction releases about 1203 kJ per 2 mol of Mg.

4. 4

   Light from heat

   That energy heats the MgO particles white-hot, and they emit light across the visible spectrum and into the ultraviolet.