MadSci Network: Physics

Re: Effect of speed of electrons on an element's physical properties

Date: Fri Sep 8 22:36:45 2000
Posted By: James Griepenburg, , Chemical consultant, Chemmet Services
Area of science: Physics
ID: 966259644.Ph

References: Alberty, Physical Chemistry, 7ed.,  John Wiley;  Chapter 12 
atomic structure,  or probably any college P. Chem. book
Chemicalc, chemical concepts corporation, a 
program that gives a lot of elemental data.
The periodic Table at

This is an interesting question and one that I have not thought about 
before.  At first blush I will say that the answer is Yes and No.   Yes, 
because the properties of an element are the sum of all the components of 
that atom and No because the physical and chemical properties of an 
element are determined mainly by the outer or valence electron 
configuration and the immediate inner electrons especially when d and f  
electrons are being added or have recently been added in the period of the 
Periodic Table.    

In order to explain the stability of the atom Niels Bohr modified the 
simple electrostatic approach to the atom and said that the electrons were 
present in the atom in discrete energy levels or orbitals.  This approach 
allows an orbital radius and electron speed to be calculated for the H 
atom electron, however, that does not mean that the electron behaves so.  
The electron in an H atom has a speed according to those calculations of 
about 2e6 m/sec.  Calculations for the heavier elements are doubtful but 
for a 1 electron atom of Z=100 the speed could be about 2e8 or 2/3 the 
speed of light, relativistic, but the electron is not going to weigh a 
ton.  The picture this gives is of an electron in a high speed orbit to 
keep from falling into the nucleus.  We know that this picture is 
incorrect.  The electron, in falling into an orbital, emits the change in 
electrostatic energy as a photon.  The picture is not one of conservation 
of energy as a falling baseball in a gravity field, but more like the 
baseball after it is caught and the PE to KE to heat and pain are 
completed and the surprise is still there.  The electron is in its energy 
level and interacts minimally with the nucleus.  It must interact because 
certain nuclei will capture a 1s electron [K capture].  The effects of 
increased electrostatic attraction are manifested in a smaller 1s orbital 
volume and shorter electron wavelength with increasing Z.  This might 
manifest itself in changes in mass defect or possibly in K Xray emission 
for the heaviest elements; [this is pure conjecture on my part].

The Chemicalc program and the Web periodic table have graphs of many 
physical properties of the elements.  These graphs show the periodic 
nature of these properties rather well.  However, the periodicity does 
seem to break down or be more complicated for the heaviest elements.  This 
is because the outer d and f filled orbitals are being pulled in closer to 
the nucleus as Z increases and their contribution to shielding increases 
rapidly with Z.  This change in shielding affects the properties of the 
atoms and also lessens the effect of the nucleus.

My conclusion is that the speed of the electrons cannot be described well 
and that the deep inner electrons after their shielding effect is 
considered have minimal to no effect on the chemical and physical 
properties of the bulk elements.   I also discovered that there is a lot I 
do not understand about electrons in an atom and am open to additions or 

Becoming a Mad Scientist,  Jim Griepenburg.

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