• Principal Quantum Number, n
• Azimuthal Quantum Number, l
• Magnetic Quantum Number, ml
Exercise
• What are the similarities and differences
between the hydrogen atom 1s and 2s
orbitals?
• For n=4 what are the possible values of l and
m?
• give the values for n, l, m for
a. 2p
b. 5d
c. 5f
Main
Energy
Level
No. of
Sublevel
Identity of
Sublevels
No. of
Orbitals
(n2)
Max. No. of
Electrons
(2n2)
1 1 1s 1 2
2 2
2s
2p
1
3
2
6
3 3
3s
3p
3d
1
3
5
2
6
10
4 4
4s
4p
4d
4f
1
3
5
7
2
6
10
14
Electron Spin Quantum Number, m
• Two possible values are allowed
+ ½ and - ½
• Opposite directions
Can two electrons in an atom have the
same set of quantum numbers?
Pauli Exclusion Principle
• No two electrons in an atom can have the
same set of four quantum numbers, n, l, ml,
and ms.
• An orbital can hold a maximum of two
electrons and they must have opposite spins.
Electron Configuration
• The way in which electrons are distributed
among the various orbitals of an atom
Aufbau Principle
• Electrons occupy orbitals of lower energy first.
The relation between orbital filling and the periodic
table
The relation between orbital filling and the periodic
table
Hund’s Rule
• For degenerate orbitals, the lowest energy is
attained when the number of electrons with
the same spin is maximized.
Orbital Diagram
Anomalous Electron Configuration
Example:
Chromium
Copper
• Consequence of the closeness of the 3d and
4s orbital energies.
• Minor departures from the expected
• Not of great chemical significance
Seat work
Write the electron configuration and the
electron orbital diagram for the following
elements.
1. Cl
2. Os
3. Cs

Electron configuration