• Question: why is hydrogen on the periodic table twice?

    Asked by marybarry to Damien, Rachael, Simon, Suzi, Tim on 18 Jun 2011.
    • Photo: Tim Fosker

      Tim Fosker answered on 17 Jun 2011:

      Hi @Marrybarry

      Hydrogen is only in the periodic table once. May be you have a table where Hydrogen is printed a second time as a key (example) to identify what the numbers for element mean?

      I hope that explains it.

    • Photo: Suzi Gage

      Suzi Gage answered on 18 Jun 2011:

      Hi @marybarry
      I had a look on the internet, and you are right, sometimes in an extended periodic table hydrogen can appear twice (although only in old fashioned ones!). This is because it’s quite unstable so there are 2 common forms of it, which behave quite differently from each other. All elements are grouped on the periodic table with other elements that behave like them. So one type of hydrogen groups with alkali metals, and one type behaves like halogens.

      However these days as Tim says it’s only on there once, in it’s ‘alkali metal’ position.

      Hope this helps 🙂

Comments

  • Photo: marybarry

    marybarry commented on :

    thank you! but why is it unstable? I thought only radioactive atoms were unstable..

  • Photo: Suzi

    Suzi commented on :

    HI Mary
    This is a great question! It’s not unstable in the same way, it’s unstable because it only has one electron, in only one shell. This shell should have 2 electrons to be complete, so it either shares this electron with another atom, or take an electron from another atom. Depending on which it does, will determine which group it’s in.

    Radioactive elements are unstable because their nuclei are unstable (their protons and neutrons) rather than their electrons.

    Hope this makes sense!

  • Photo: Tim

    Tim commented on :

    Thanks @marybarry (& @suzi) for that. Another thing I’ve learnt. I’m glad Suzi found this out I’ve never seen it actually listed twice. Very interesting 🙂