Atomic Structure
Electron Configurations
• The way electrons are arranged around the
nucleus
Standard Notation
of Fluorine
2
1s
Number of electrons
in the sub level 2,2,5
2
2s
5
2p
Sublevels
Electron Configuration
• Energy level of an electron is the region around the
nucleus where it is likely to be moving
– N = 1, 2, 3 ,4
• Within each energy level are sub-levels
– s, p, d and f
• Each sub-level corresponds to a different cloud shape or atomic
orbital
• Atomic orbital is a region where there is a high probability of
finding an electron
• Each type of orbital has a unique shape:
– s orbitals have a spherical shape (1 orbital)
– p orbitals have a dumbbell shape (3 orbitals)
– d and f orbitals have more complex shapes (5 orbitals, 7 orbitals)
Electron Configurations
• Lowest energy level (n=1) has only 1 sub-level:
– 1s
• Second energy level (n=2) has 2 sub-levels:
– 2s and 2p
• Third energy level (n=3) has 3 sublevels:
– 3s, 3p and 3d
• Fourth energy level (n=4) has 4 sub-levels:
– 4s, 4p, 4d and 4f
Electron Configurations
• How electrons fill the orbitals is based on 3
rules:
– The Aufbau principle
– The Pauli Exclusion principle
– Hund’s rule
Orbital
Diagram
Electron Configurations
• The Pauli exclusion principle
– Atomic orbital may describe at most 2 electrons
– Electrons must have opposite spins
– ↑↓
Electron Configurations
• Hund’s rule
• In a set of orbitals, the electrons will fill the
orbitals in a way that would give the maximum
number of parallel spins (maximum number of
unpaired electrons)
•
↑
↑
↑
• Analogy: Students could fill each seat of a school
bus, one person at a time, before doubling up.
1s1
Orbital
Diagram for
Hydrogen
Orbital
Diagram for
Helium
1s2
Orbital
Diagram for
Lithium
1s22s1
Orbital
Diagram for
Beryllium
1s22s2
Orbital
Diagram for
Boron
1s22s22p1
Orbital
Diagram for
Carbon
1s22s22p2
Orbital
Diagram for
Nitrogen
1s22s22p3
Standard Notation
of Fluorine
2
1s
Number of electrons
in the sub level 2,2,5
2
2s
5
2p
Sublevels
Electron Configurations
Electron Configurations
Electron Configurations
• What is the electron configuration for?
– Hydrogen
– Lithium
– Fluorine
Electron Configurations
– Sodium
– Sulphur
– Rubidium
– Complete the following worksheets
– Electron Configurations Level 1
– Electron Configurations Level 2
– Electron Configurations Worksheet 4