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Lanthanoids and Actinoids as separate tables

  1. Dec 2, 2004 #1


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    Physcis 101 question:

    The periodic table as far as I can recall, is always illustrated with the Lanthanoids and Actinoids as separate tables and the main table compressed.

    I understand these elements are surely closely related by common characteristics, but is there a reason that they are always illustrated this way, or is it really more a matter of display-space constraints? (If they were in the main table, the chart would be very long and short.) Space constraints notwithstanding, would a single, long table be the most faithful portayal of the elements?
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  3. Dec 2, 2004 #2


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    The reason of spacing and the general "look" of the periodic table of elemets are of quite significance,but it's the physical and the chemical properties of those elements that make us build the table in that manner.The reason why ther're called "lantan-oids" and "actin-oids" is pretty obvious from the way i've written the words.Each of those 14 elements is similar both wrt to physical and chemical properties to either "lantan" or "actinium".So the reason why we chose symmetry and not antisymmetry in the table of elements is scientifically explainable.
  4. Dec 2, 2004 #3


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    Yes, I understand well the reason the table is built the way it is. I understand the S-, P- and D- orbitals and the way these cause the various elements to behave similarly. This leads us to group them logically by behaviour & properties, and thus are represented in groups in the table.

    I just don't understand why only the actinoids and lanthanoids are broken out especially. I mean, if you were breaking out groups of elements, you could do that with any group: all the metals, or all the noble gases for example.

    Putting it another way: is there a reason why the Acts and Lans *don't* belong in the table proper?

    Or, visually, why is the table never displayed like this:
  5. Dec 2, 2004 #4
    The reason those elements are grouped is because the way their f orbitals are filled. The basically form the f-block (not sure if it's actually called that way though), similar to how the transition metals form the d-block, so called because the properties there are dominated by the d orbitals.

    I think they only separate it becasue of space constraints. They then align them according to the state of the d orbitals, such that they fit the rest of the table.

    Btw, that gif is not accurate, AFAIK - she Scandium and Yitrium should go on the left side of the gap.
  6. Dec 14, 2004 #5


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    that gif is not accurate

    That would be alarming, since it was derived direactly from the homepage ofwebelements.com
  7. Dec 14, 2004 #6


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    Webelements likes to display the Periodic Table slightly differently than the conventional form. They have Lutetium and Lawrencium under Yttrium, instead of at the end of the lanthanides and actinides. A purist would frown upon this because, Lanthanum and Actinum are definitely better candidates for these positions, in terms of the electronic configuration. But I guess the high degree of similarity in the configurations of Lu and Lr was the reason why Webelements decided to "cheat" and pick a more visually simple representation.

    But to answer the original question, yes, the main reason for the current format is the appearance. A "long form" (and that is exactly what it is called) of the Periodic Table does exist. Here it is.
  8. Dec 15, 2004 #7
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