Electronic Configurations
Electronic Configurations
We know how to write electron
configurations, but the following is a
quick review and it describes using
the noble gas core in configurations.
Electron Configurations
How electrons fill their orbitals
Pauli Exclusion Principle
 Each orbital can hold a maximum of
TWO ELECTRONS
Aufbau Principle
 Electrons fill orbitals that have the
LOWEST ENERGY FIRST
Electron Configurations
Type of
Orbital
s
p
d
Number of
Subshells
Total # of
Electrons
1
2
3 (px, py, pz)
6
5
10
Electron Configurations
Example of an electron configuration:
Fluorine has 9 electrons
1s22s22p5
Remember, when writing configurations, each
atom contains the same configuration as
the one before it, we just add on one
electron.
Electron Configurations
Using the noble core method:
Instead of writing the whole
configuration from hydrogen, you can
instead use the previous noble gas
core configuration:
Sulfur: 16 electrons
[Ne] 3s23p4 - core configuration
instead of: 1s22s22p63s23p4
Electron Configurations
You can also use the periodic table to
help you write configurations:
Electron Configurations
New information:
When electrons fill the p orbitals and
above they do so by filling one
electron in the px, then the py, then
the pz. These orbitals are called “half
full.”
Electron Configurations
Notice that each orbital has an electron that
points up and one that points down. YOU
CAN NEVER HAVE TWO ELECTRONS
POINTING THE SAME WAY!!!!
If they do, they add their energies, which is
forbidden.
It also violates the PAULI EXCLUSION
PRINCIPLE THAT NO TWO ELECTRONS CAN
HAVE THE SAME QUANTUM NUMBERS.
Electron Configurations
This is known as HUNDS RULE: for an
atom in the ground state, the number
of unpaired electrons is the maximum
possible and these electrons MUST
HAVE THE SAME SPIN.
Electronic Configurations
Notice that each orbital has an electron that
points up and one that points down. YOU
CAN NEVER HAVE TWO ELECTRONS
POINTING THE SAME WAY!!!!
If they do, they add their energies, which is
forbidden.
It also violates the PAULI EXCLUSION
PRINCIPLE THAT NO TWO ELECTRONS CAN
HAVE THE SAME QUANTUM NUMBERS.
Electron Configurations
Hunds Rule explains why Chromium,
Coppper, etc., have strange electron
configurations.
For Chromium it is: [Ar]4s13p5
If you look at the spins of the electrons
for the 4s13p5 electrons, you have:
____ ___ ___ ___ ___ ____
4s
3d
Electron Configurations
According to Hunds Rule, this
configuration gives Chromium and
very low energy level, resulting in a
stable atom.
Electron Configurations
For copper, moving the 4s electron to
the 3d energy level results in a full
energy level, also making the atom
stable.
Copper: [Ar]3d104s1
____ ____
4s
____
____
3d
____ _____