 |
 |
Electron Transition and Energy
Name: Leaf L.
Status: student
Age: 17
Location: N/A
Country: N/A
Date: 3/22/2004
Question:
When an atom is excited to certain degree, electrons
tend to escape from its attraction with nuclear charge,since energy level of
3p is higher than 4s, then why the electron that escapes first is from
4s in stead of 3p?? Isnt the electron in 3p possess higher energy?
Replies:
In the H atom (single electron) the energy of the 3p and 4s states are
97492 cm^-1 and 102824 cm^-1 above the ground state (taken as 0 energy),
respectively. So the energy of the 3p orbital is lower than the 4s. This
isn't to discount your question, however, because in "real" atoms around the
4s, 3p, and 3d orbitals the screening of the nuclear charge by lower energy
electrons DOES scramble the energy levels from the 1 electron order. So for
example:
for potassium, calcium and scandium Z= 19, 20, 21 respectively the energy
levels in cm^-1 above the ground state (taken as 0 energy for each) is as
follows:
K 4s, 4p, 5s, 3d, 5p, 4d //0, 13000, 21026, 21535, 24710, 27400
Ca 4s2, 4s4p, 3d4s, 3d4s, 4s4p, 4s5s//0, 15210, 20350, 21850, 23650, 31540
Sc 3d4s2, 3d24s, 3d4s4p//0, 11600, 15000, 15800
You can see that there is a lot of scrambling of states. In the case of
Ca the pair of states labeled 3d4s differ in the direction of the electron
spin of the outermost electron. If you want to see how the atomic states
become intertwined as the Z increases look up:
http://physics.nist.gov/cgi-bin/AtData and you will find the data for most
of the lower half of the periodic table. It makes for interesting study.
Vince Calder
Click here to return to the Chemistry Archives
| |
Update: February 2012
|
|
