• Question: how come when you burn Mg a light appears and not on other metals

    Asked by llogk to Ahmed, Francesca, George, James, Nitheen on 13 Nov 2014.
    • Photo: James Sullivan

      James Sullivan answered on 13 Nov 2014:

      because energy is released when Mg reacts with oxygen.

      when the reaction happens on Mg it is very fast and all the energy is released at the same time.

      when the reaction happens with other metals – say iron – the reaction is far slower and the energy is released over a far longer timescale

    • Photo: Francesca Paradisi

      Francesca Paradisi answered on 13 Nov 2014:

      But other metals also give you a coloured flames, for example Lithium burns red, Sodium yellow, Potassium violet!

    • Photo: Ahmed Osman

      Ahmed Osman answered on 17 Nov 2014:

      Hi llogk
      Thank you for your question!
      Magnesium is in Group 2 of the periodic table. This means that magnesium has 2 electrons in its outer shell making it highly reactive to oxygen. When putting magnesium metal in fire you are supplying enough energy so that magnesium can start reacting with oxygen in the air to form magnesium oxide. The reaction of magnesium with oxygen releases a huge amount of energy which you can see as heat and bright light.
      Be careful when burning magnesium though, because it also produces ultra-violet (UV) light which can damage your eyes if you stare at it for too long.
      For manganese, copper, sodium and many other metals, this photon frequency is in the range that’s visible to humans, and a colour is produced, which is just what white looks like if you subtract this particular frequency (a visible photon’s frequency is a colour). For magnesium, the frequency is larger, and ultraviolet light instead of visible is subtracted, so the flame appears white.

    • Photo: George Dowson

      George Dowson answered on 19 Nov 2014:

      When metals burn, large amounts of energy is released, much in the form of heat and light (two sides of the same coin).
      Low heat is not visible to us as the light it emits is in the infrared region but if the reaction is hot enough, the material will generate dull red, orange and blueish light depending on the heat. Magnesium, like Ahmed says, burns so hot some of the light is in the ultra violet, so “blue” we can’t see it.

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