Subject: Summary: Energy levels of atomic orbitals (calculated/experimental) as functions of nuclear charge.

From: Laurence Lavelle <[email-masked]>
Date: Sat, 31 Oct 1998 20:36:01 -0800

Thank you for your comments. Individual responses are below.
The NIST Physical Reference Data
(http://physics.nist.gov/PhysRefData/contents.html) is an excellent
resource for electron configurations.
I believe the correct way to write electron configurations is to indicate
the ground state such that the last orbital represents the highest energy
orbital. 
Giving Titanium as an example: Ti  [Ar] 3d^2  4s^2.  
This clearly shows that Ti+ is [Ar] 3d^2  4s^1.

This appears a viable solution until one asks why the 4s^2 in Ti do not
enter the lower energy unoccupied 3d orbitals?

Laurence 

>Date: Thu, 29 Oct 1998 10:22:57 +0100 (MET)
>From: Habbo Heinze <[email-masked]>
>To: Laurence Lavelle <[email-masked]>
>Subject: Re: CCL:Energy levels of atomic orbitals
(calculated/experimental) as  functions of nuclear charge.
>
>
>Have a look at 
>
>  NIST Physical Reference Data
>  http://physics.nist.gov/PhysRefData/contents.html
>
>specifically
>
>  Ground Levels and Ionization Energies for the Neutral Atoms
>  http://physics.nist.gov/PhysRefData/IonEnergy/ionEnergy.html
>
>Maybe this data is helpful
>
>Cheers
>
>Habbo

>Date: Thu, 29 Oct 1998 16:29:31 -0400 (AST)
>From: "J. Sichel" <[email-masked]>
>
>According to CE Moore's compilation of Atomic Energy Levels, the
>experimental ground state is Sc(3d 4s2 2D 3/2).
>
>     John-M. Sichel
>     Dept. de chimie et biochimie
>     Universite de Moncton
>     Moncton NB, Canada    

>Date: Thu, 29 Oct 1998 08:00:07 -0500 (EST)
>From: Robert Zellmer <[email-masked]>
>
>I'm not sure the 3d^1 4s^2 is necessarily written this way because of energy
>considerations.  Generally, one thinks of the 4s^2 3d^1 configuration as
being
>correct due to energy considerations and since the 4s is full one would
expect
>this.
>
>It may be possible that the 3d is lower in energy than the 4s. However,
>I believe that the 3d^1 4s^2 configuration is often written to convey the
fact
>that the 4s is the valence shell (although most consider the 3d as part of
the
>"valence" for transition metals since it is only partailly occupied in
most cases
>and certainly is an important part of the chemistry of these elements).
Written
>in this way students can "see" the valence shell (shell with highest n
value).
>
>When the configuration is written as 4s^2 3d^1 this shows that the 4s is
filled
>before the 3d since it is lower in energy.  This is also a convienent way
to write
>the configuration since this is the way it gets filled by using the periodic
>table (ns before (n-1)d).  So even in cases when the 3d may be lower in
energy
>it is still written this way.  Think of the "exceptions" Cr and Cu in the
>first transition metal period which have the config. 4s^1 3d^5 and 4s^1
3d^10,
>respectively.  These get filled in this way due to shifts in the energies of
>these subshells and we usually tell students that 1/2 filled and full
subshells
>have an "extra" stability.
>
>I think it would be very confusing to students if you changed the order
everytime
>these orbitals changed order due to changes in energy.  I usually stick
with the
>4s 3d ordering and tell them they may see it as 3d 4s since in this way the
>valence shell is on the "outside".
>
>I think I have seen a graph of the relative energies of these levels as
one moves
>through the PT.  I will see if I can locate it.
>
>
>Robert J. Zellmer

>From: "Huff, Tom" <[email-masked]>
>
>I would appreciate a copy of your inputs assuming they are not posted in a
>summary on the CCL.  My wife teaches first year chemistry and these are her
>comments at a first year chemistry level.
>
>I believe
>the problem may simply be that different textbook use different notations in
>writing the electron configurations.  Some write the electron configurations
>by shells (so 3s 3p 3d then 4s etc.); where others are writing the
>configuration by energy (3s 3p 4s 3d).  On the other hand Judy and I have
>discussed several times the fact that the electrons fill in one order (4s
>before 3d) but are removed in different order (4s before 3d).  I believe
>experimental evidence confirms that the 4s fills first (when there are no 3d
>electrons) but as you begin adding 3d electrons there will be additional
>shielding of the nucleus making the effective nuclear charge less and
>therefore higher energy for the 4s when there are one or more 3d electrons.
>
>
>Tom Huff