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Periodic Table, Lanthanides and Actinides
Name: Stuart
Status: educator
Grade: 6-8
Location: N/A
Country: N/A
Date: February 2007
Question:
I have been looking into these actinides and
lanthanides and why they are not in the periodic table and the
usually excuse is the space,,, I realise that the lanthanides and
actinides are filling the 4F and 5F shells. I am confused over what
the periodic table would look like if they were in it? Am I to
presume periods 6,7 seven would be really long with a thin bit
in the middle (where we chuck in the lanthanides and actinides)
until we start with the 'normal' transition metals filling the D
shells? I just want to know for my own reference, and just incase
some kid asks me whilst they are putting them in atomic order....
Replies:
Here is a good web site that discusses the issue with references.
http://www.theschemata.com/conventional_periodic_table.html
I think it is helpful to remember that the periodic table is an
organizational tool that attempts to show relationships among
element properties. How we arrange the elements is really a matter
of what we want to represent or emphasize.
Greg (Roberto Gregorius)
The lanthanides and actinides are in the periodic table, but the table
is usually displayed in a more compact form for, as you say, reasons of
space. If the periodic table were displayed fully extended, it would
have the lanthanide row between lanthanum and hafnium and the actinide
row between actinium and rutherfordium. There would be a break in the
transition metal section between calcium and scandium and between
strontium and yttrium, just as there is already displayed a break
between hydrogen and helium, between beryllium and boron, and between
magnesium and aluminum. The table would be a lot longer in display than
it is now.
You can see an "extended" periodic table of this design taken to an
absurd degree (up to element 218) on Wikipedia at
http://en.wikipedia.org/wiki/Periodic_table_(extended).
Another version, placing the familiar table on its ear, is at
http://www.apsidium.com/. There are a ton more links on the web.
Richard Barrans
Department of Physics and Astronomy
University of Wyoming
I understand your frustration. The problem is that when the
"traditional" periodic table was designed, little or nothing was
known about the lanthanides and actinides, so no accommodation was
made for those elements. There are a number of web sites that offer
alternative illustrations of the periodic table. However, I am not
sure that any take the long lanthanide and actinide series filling
the "f" orbitals in a very visually satisfactory way. The
"explanation" is that the traditional periodic table allows one to
organize a vast amount of experimental and theoretical information
in a concise form. That does not mean that it is dogmatic and
without its limitations. You do not have to make "excuses" for the
fact that it does not explain the entire number of elements that
exist, or may exist. It is still a very useful tool.
Vince Calder
Stuart!
They are "in" the periodic table.
Just not in a pretty place.
Just as the transition metals make a long extension shoe-horned between
Column2a (Mg/Ca and Column3a (Al/Ga),
the rare earths make an even longer extension between Column2a and the
transition metals.
Drawing it in that position would make the table too wide to fit a page
nicely, so they drop it into a new box below the whole table.
There are all kinds of interesting "other appearances" of periodic table on
the web -
go look at them. I will get the URL's later.
They all have the same or similar topology, just pushed around to fit our
page representations better.
The whole point of most is to repair the appearance that the rare earths
make the table "break down".
In these others, they look like just another naturally-occurring generation
of quantum numbers,
albeit of a pattern we would not normally think up ourselves.
Looking at these makes me realize that the periodic table is,
by definition, whatever human idealization that begins to fit the
quantum-number pattern of the elements.
Jim Swenson
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