Energy Level Diagrams
Creating Energy-Level Diagrams
• The electrons occupy specific energy levels in the
atom. The energy-level diagram is a method of
representing an atom’s distribution of electrons
throughout the various energy shells (n) and
subshells or orbitals (l ).
• The energy-level diagrams can be extended to
include all four quantum numbers.
• Experimental information about atomic matter
shows that there are relationships between orbitals
and their energy levels. Conventions have been
established to attend to these observations.
Conventions for Creating Energy-Level Diagrams
• Pauli exclusion principle –
– no two electrons in an atom may have the same four
quantum numbers
– no two electrons in the same orbital may have the same
spin
– only two electrons with opposite spins may occupy an
orbital
• aufbau principle – (German for “building up’)
– each electron is added to the lowest available energy
orbital
• Hund’s rule –
– one electron is placed in each orbital at the same energy
level before the second electron is placed
Conventions for Creating Energy-Level Diagrams
• Circles or squares are used to represent the
orbitals
• Arrows are used to represent the electrons
– up represents one electron rotation (clockwise)
while down the other (counter clockwise)
– there is no convention as to which one you must
start with
Conventions for Creating Energy-Level Diagrams
O
(z = 8)
1s
2s
2p
3s
3p
P
(z = 15)
1s
2s
2p
3s
3p
1s
2s
2p
3s
3p
Ar
(z = 18)
Conventions for Creating Energy-Level Diagrams
•Energy-level diagrams may be written in a vertical manner
to exemplify the energy level subtleties.
6e10e14e2e-
32e-
4d
6e10e2e-
18e-
3d
6e10e2e-
18e-
6p
5d
4f
6s
5p
5s
4p
3p
3s
2p
2s
1s
Order of filling orbitals
4s
6e2e-
8e-
6e2e-
2e-
•As the number
of energy levels
and orbitals
increase, so too
does the
complexity of the
energy-level
diagram.
8e-
2e-
•The diagram
indicates nicely
the order in
which the orbitals
are filled
Energy-Level Diagrams for ions
• The energy-level diagram is created in the same
manner as the regular atom. However, a surplus or
deficit of electrons are included.
– For anions – add the proper number of electrons using
regular conventions
S 2(z = 16)
1s
2s
2p
3s
3p
– For cations – remove the correct number of ions in the
proper manner
Al 3+
(z = 13)
1s
2s
2p
3s
3p