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Definition of transition metals confusion

Discussion in 'Science' started by leftieM, Mar 4, 2012.

  1. leftieM

    leftieM New commenter

    I'm teaching A2 for the first time (eek!). My understanding of transition metals is that they can form an ion with a partially filled d-sublevel so there are d-d electron transitions and therefore a colour. This is the definition I have in a revision book and it makes sense.
    In the AQA spec it says that a transition metal is one with an atom <u>or</u> ion with an incomplete d-sublevel. Now, by this definition Sc is a transition metal, having 4s2 3d1 but it is not and AQA are giving the TMs as Ti-Cu.
    I'm obviously missing something here. How can the AQA definition stand unless Sc is counted as a TM?
     
  2. Ssn77

    Ssn77 New commenter

    There is some variability about this, as some definitions include metals and stable ions, some only include stable ions. The first would include Sc, the second would not (stable ion is Sc3+).


    The AQA specification is inconsistant, but since it gives the metals that are included, I go with those. It is worthwhile asking the question why Sc is often not included as a TM while you are teaching the topic. Since one of the characteristics of a TM is coloured salts (according to AQA), that would fit in with excluding scandium.


    Another reason for discussing this with a class, apart from a greater understanding of the topic, is AQA do have a habit of slipping in the odd question that seems to have been excluded by the specification. Last summer's Chem 1 paper asked for the structure of Na, although the spec stated Mg, and disallowed the mark if you put a hexagonal arrangement of atoms which is correct for Mg (in spec), but not for Na (not in spec).
     
  3. phlogiston

    phlogiston Star commenter

    Hi Leftie
    I (and the texts I've read) are in agreement with the definition of ions with part filled d orbitals, thus excluding Sc. I've never seen a definition of TM from proper chemists that includes Sc.
    AQA can do strange things. They once published a GCSE reactivity series with Pt under gold, (which it's not). That's another story though.
    P
     
  4. In every 'normal' reactivity series that has ever been printed, Pt is under Au. The exception is the electrochemical series where Li and Na are reversed too! I don't therefore consider AQA as being 'strange' in putting Pt lower than Au in their series.

     
  5. Ssn77

    Ssn77 New commenter

    The IUPAC gold book (chemical definitions) gives a transition metal as, "An element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell". So, I think it is worth making students aware of both definitions, especially as it should lead to a greater understanding of the chemistry.
     
  6. leftieM

    leftieM New commenter

    Thank you all for the replies. I get it now. Sc is a transition element by the IUPAC definition but Zn is not. My revision book is incorrect. I'll make sure the pupils understand that they will see both definitions and which one they need to put into their exam.
     
  7. Ssn77

    Ssn77 New commenter

    Scandium does not show typical properties of a transition metal (coloured compounds, variable oxidation state leading to use as a catalyst); I think this is what the revision book is getting at. It is being incomplete rather than incorrect.
     
  8. Remember that Copper (I) [being a 3d10 ion]is not transitional but Copper (II) is.
    That makes an interesting question: why when ioniation is endothermic is queous chem of copper dominated by the +II oxidation state?

    That's a better poseer for your students

     
  9. remeber that copper (I) [3d10] is not transitional under your definition but copper (II) will be [3d9]

    ask your students why the aqueous chemistry of copper is dominated by the +2 ion when ionisation is endothermic, and the copper (I) ion has the famously stable [!} "full shell of electrons"...
     
  10. Ssn77

    Ssn77 New commenter

    Excellent question....though as many of my students would struggle to work out the formulae of Cu(I) and Cu(II) compounds (I have a very lazy U6 year unfortunately), I think their brains might just explode if I asked them that!
     

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