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    As we move across period 4 we notice that the atomic radii of the transition metals remains fairly constant with only a small decrease across the period.

    The explanation for this is that new electrons are added to the 3d orbital and hence do not offer adequate shielding.

    I do not understand this explanation.... Could you please explain it ?
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    Please do have a look at this if you have the time.



    (Original post by illusionz)
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    (Original post by Ari Ben Canaan)
    As we move across period 4 we notice that the atomic radii of the transition metals remains fairly constant with only a small decrease across the period.

    The explanation for this is that new electrons are added to the 3d orbital and hence do not offer adequate shielding.

    I do not understand this explanation.... Could you please explain it ?
    It is known that the 3d shell is inside the 4s shell (remember the 4s electrons are the first to be lost when the atoms are ionised), so electrons are being added to a shell that increases the shielding on the 4s.

    At the same time the increasing number of protons in the nucleus increase the attraction on the 4s electrons.

    These two effects pretty much cancel out.
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    (Original post by charco)
    It is known that the 3d shell is inside the 4s shell (remember the 4s electrons are the first to be lost when the atoms are ionised), so electrons are being added to a shell that increases the shielding on the 4s.

    At the same time the increasing number of protons in the nucleus increase the attraction on the 4s electrons.

    These two effects pretty much cancel out.
    I have read on another website that as we keep adding more electrons to the 3d sub shell we begin to see increasing 3d electron-electron repulsion, hence, the radius begins to actually expand after a time. Is this true ?
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    (Original post by Ari Ben Canaan)
    I have read on another website that as we keep adding more electrons to the 3d sub shell we begin to see increasing 3d electron-electron repulsion, hence, the radius begins to actually expand after a time. Is this true ?
    No, the radius decreases slightly across the 1st row transition metals.
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    (Original post by charco)
    No, the radius decreases slightly across the 1st row transition metals.
    Quick question, why is it that the 3d subshell is so poor at shielding the 4s electrons ? Is it because when the 3d orbitals are combined we obtain an asymmetrical spherical shell that isn't so good at counteracting the positive nuclear charge ?

    EDIT : Is there anything else you can tell me about the trend in atomic radius for the d block elements ?



    Also, the above image shows a clear decrease in radius at first, then a near constant radius followed by a slight increase. What is the reasoning behind these three things ?
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    (Original post by Ari Ben Canaan)
    Quick question, why is it that the 3d subshell is so poor at shielding the 4s electrons ? Is it because when the 3d orbitals are combined we obtain an asymmetrical spherical shell that isn't so good at counteracting the positive nuclear charge ?

    EDIT : Is there anything else you can tell me about the trend in atomic radius for the d block elements ?



    Also, the above image shows a clear decrease in radius at first, then a near constant radius followed by a slight increase. What is the reasoning behind these three things ?
    3d orbitals are poorly shielding as they are, to quote my tutor 'radially diffuse'
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    If you look at the wavefunctions for p and d orbitals, you will see that p orbitals are more penetrating, as in there is a higher probability of electrons in a p orbital getting closer to the centre of an atom than electrons in a d orbital. Hence, adding electrons to a d orbital will have less of a shielding effect because the electrons have a far lower probability of getting closer to the nucleus and hence shielding other electrons.
    I hope that helps! If you want to see a diagram there's one on page 15 of this PDF :
    file:///C:/Users/Daisy/Downloads/DPTX_2013_2_11320_0_410059_0_140 108.pdf
 
 
 
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