MadSci Network: Physics
Query:

Re: What causes the differnce in intensity of the lines of the Balmer series

Date: Fri Aug 6 07:57:02 2004
Posted By: James Griepenburg, , Chemical consultant, Chemmet Services
Area of science: Physics
ID: 1087865185.Ph
Message:

From: Allan Ewings
Grade: 10-12
City: Sydney, State/Prov.: NSW Country: Australia
Area: Physics Message ID Number: 1087865185.Ph

We are given that one of the down falls of the Bohr model of the atom was 
its 
inability to account for the difference in intensity of the lines of the 
Hydrogen 
spectra.
How was that difference accounted for in later models?

Bohr developed his theory to describe the behavior of hydrogen atoms with 
light.  As such it was and is quite a good theory and when elaborated by 
the revelations of wave and quantum mechanics it allows a good basic 
understanding of what’s going on in the hydrogen atom and hydrogen-like 
ions such as He+ and Li++.  Bohr’s theory describes transitions well but 
has no ability to describe the states of an atom these are described by 
wave mechanics, quantum mechanics and relativity.  Descriptions of the 
states[1s, 2s, 2p,3s, 3p, 3d etc] allow the development of selection rules 
and calculation of transition probabilities.  This and aspects of the 
quantum-wave mechanics theory are described elegantly in “Atomic Spectra 
and Atomic Structure” by Gerhard Herzberg.

Others and I have discussed this before; search the Mad Scientist 
using “Balmer  Series”.  Check it out.  I have one comment on the answer 
about the helium ion spectrum, the effect of increased nuclear charge 
increases the transition energies by a factor of 4 for He + and 9 for Li 
++. 

The following site  http://physics.nist.gov/Pubs/AtSpec/node17.html  describes selection rules 
and gives emission and absorption intensities.

All this considered the main contributor to the observed spectra is the 
distribution of states that the atoms are in. [This depends on the 
temperature [Boltzman distribution] ], the concentration of atoms usually 
the more the merrier,  the presence of radiation flux that can alter state 
distribution thru photoexcitation or stimulated emission [lasers].  For 
example the balmer emission series is possible if there is a distribution 
among the n=2,3,4, etc states at too low a temperature or too high a 
temperature it diminishes.  Similarly the absorption spectrum is observed 
with a high population of the n=2 state and is seen at lower 
temperatures.  This is generally true for any atomic emission-absorption 
lower T shows absorption spectra; higher T shows emission spectra.

If you are interested in spectroscopy I recommend Herzberg’s books



Current Queue | Current Queue for Physics | Physics archives

Try the links in the MadSci Library for more information on Physics.



MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci


MadSci Network, webadmin@www.madsci.org
© 1995-2003. All rights reserved.