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Date: Thu, 4 Oct 2001 19:26:33 +0300 (EET DST)
From: Mikael Johansson <mpjohans ":at:" pcu.helsinki.fi>
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To: Ulrike Salzner <salzner(+ at +)fen.Bilkent.EDU.TR>
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Subject: Re: CCL:size of s,p,d orbitals
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Hello Ulrike and All!

On Thu, 4 Oct 2001, Ulrike Salzner wrote:

> until 1 hour ago, I firmly believed that p-orbitals are larger than s-
> orbitals for atoms that are in the same row of the periodic table. Only
[...]
> third year students. She told me that she was surprized that the students
> did not know that the order according to decreasing size is s > p > d
[...]
> The question now is: Do the two ways to determine the size of the orbitals
> lead to different conclusions? Is there a mistake somewhere? Is there
> newer information? Which orbitals are bigger? What is best method to
> determine the size to explain bonding, hybridization, or lack thereof and
> so on?

This was an interesting question, succeeding in diverting me from things I
should be doing :-)

Without taking a stand on what method is the "best" I made a quick
calculation on the argon-atom and compared the "sizes" of the 2s/2p and
3s/3p orbitals. Below is reported the radius of a spherical boundary
around the atom which contains 90% resp. 95% of the electron density of
the orbital in question: (the calculation was made on B3LYP/TZVP level,
for no specific reason)

    90%   95%
2s  0.65  0.74 a.u.
2p  0.63  0.72
3s  2.14  2.44
3p  2.64  3.06

So according to the above the 2s/2p-orbitals are about as big, whereas
the 3s is smaller than the 3p.

Other comments on the subject would be very welcome!

Have a nice day,
    Mikael Johansson
    University of Helsinki
    Department of Chemistry
    mikael.johansson "-at-" helsinki.fi
    Phone: +358-9-191 50185
    FAX  : +358-9-191 50169