• Question: why does sulphur + oxygen become sulphur dioxide, and not sulphur oxide?

    Asked by misaki to Mike, Pip, Tianfu, Tim, Tom on 26 Jun 2012.
    • Photo: Tom Lister

      Tom Lister answered on 26 Jun 2012:

      Ask the chemist (Pip), but I believe it is because Sulphur is a very popular character and Oxygen just can’t get enough of him.

    • Photo: Tim Stephens

      Tim Stephens answered on 26 Jun 2012:

      It’s to do with the free electrons that orbit the atom. Atoms are always trying to find the most stable compound to exist in, so compounds that use up all the available free electrons around the outside of the atom are preferred.
      There’s space for two Oxygen atoms to join the Sulphur atom, so they do. Pip may have a better explanation though.

    • Photo: Philippa Bird

      Philippa Bird answered on 27 Jun 2012:

      Well, it depends what level you are at. It’s a really great question though, practically degree level. You should study chemistry!
      Ok, so if you are at GCSE this is going to be a little tricky to explain. You know that atoms want to fill their outer shell to make eight electrons in their outer shell, and I guess you’re wondering because silicon dioxide would have ten with two oxygens, since the oxygens need to share two electrons. The thing you don’t learn at GCSE, but will know if you are doing A-levels, is that within the shells there are “sub” shells. These are called s,p,d and f shells. Not all atoms have all shells available to them, some (like the big block of metals in the middle of the periodic table) have all of their “d” shells filled, but some, like sulphur, have “d” shells, but aren’t using them. (Oxygen doesn’t have them at all). So the sulphur can put the extra two electrons in the spare “d” shells, and that’s why it has ten electrons around it. Sulphur can actually have even more electrons than ten in its outer shell, like SF6, or SO4(2-).
      Good luck with your chemistry, and keep asking the tough questions!

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