1. Energy Level Diagrams

2. 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.

3. 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

4. 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

5. Conventions for Creating Energy-Level Diagrams2p 3s 3p
O (z = 8) 1s 2s 2p 3s 3p
P (z = 15) 1s 2s 2p 3s 3p
Ar (z = 18)

6. Conventions for Creating Energy-Level Diagrams
Energy-level diagrams may be written in a vertical manner to exemplify the energy level subtleties.

7. Order of filling orbitals2p 3p 4p 6p 5d 4f 5p 4d 3d
2e-
6e-
10e-
14e-
8e-
18e-
32e-
Order of filling orbitals
As the number of energy levels and orbitals increase, so too does the complexity of the energy-level diagram.
The diagram indicates nicely the order in which the orbitals are filled

8. 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
For cations – remove the correct number of ions in the proper manner 1s 2s 2p 3s 3p
S 2- (z = 16) 1s 2s 2p 3s 3p
Al 3+ (z = 13)