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Explaining weird trend of d- and f- block elements.

  1. Jun 4, 2013 #1
    Hello friends,

    I noticed from Wikipedia the following information:
    Atomic radii:
    4th period(only d-block elements):
    Sc:160 pm
    Ti : 140 pm
    V : 135 pm
    Cr : 140 pm
    Mn: 140 pm
    Fe : 140 pm
    Co : 135 pm
    Ni : 135 pm
    Cu :135 pm
    Zn : 135 pm

    Normally across the period atomic radii should decrease. But d-block elements do not follow this trend. It increases From V to Cr and them remains constant and decreases and remains constant again.

    So they show horizontal similarities too.. Can some one explain me this strange trend?

    More stranger trend is of f-block elements.. They don't change their radii at all if we go across the period!!!
  2. jcsd
  3. Jun 4, 2013 #2


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    As far as I remember the experimental radii are half the distance of the atoms in a crystal lattice.
    However, the metals crystalize in different lattices, which influences the radii.
    Better take the calculated values from the table below.
  4. Jun 4, 2013 #3
    Which table? can you explain this trend?

    Not only this one,ionization enthalpy too follow the same way as atomic radii. But a little difference.

    So i thought understanding atomic radii would help to understand everything.
  5. Jun 4, 2013 #4


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  6. Jun 4, 2013 #5

    I mean that is theoretical. Shouldn't we go for experimental results?

    Yes. the theoretical models follow the general trend. But i think we should stick to experimental results..

    Do you think no satisfactory explanations can be given to the trend observed experimentally?
  7. Jun 4, 2013 #6
  8. Jun 4, 2013 #7


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    The experimental values are derived from bond lengths of covalent substances. Hence you have to discuss the average bond lengths of d-block elements in mainly covalent compounds. This is much more complicated than discussing the shrinking of d- or f-orbitals.
  9. Jun 4, 2013 #8
    So, Can We say that d-block elements follow the same periodicity of that of s- and p- blocks?

    I mean by experimental results obtained by deriving bond lengths, it is observed that some elements have same atomic radii.. i.e,they show horizontal similarities. s- and p- block don't show like that.

    but theoretical models show no horizontal similarities.
    Last edited: Jun 4, 2013
  10. Jun 4, 2013 #9
    My best guess is Slater-screening. Electrons can screen other electrons from the positively charged nucleus, but it depends on how the electrons occupy the orbitals (which itself seems random for d- and f-block elements). This way, depending on the screening of other electrons, the distance of the outer electrons from the nucleus can be very similar.
  11. Jun 5, 2013 #10
    How is Slater-screening different from Shielding Effect?
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