Electron Configuration
Electron Configuration
•
•
Electron configuration is a shorthand
notation that shows electron arrangement
within orbitals.
Electron configuration can be written in one
of 3 methods:
1. Energy-Level Diagrams (orbital diagram)
2. Complete electron configuration
3. Condensed electron configuration (AKA noble gas
configuration)
Electron Configuration
Principal quantum
number “n”
Secondary quantum
number “l”
Energy Level Diagram
Pauli’s Exclusion Principle
• No two electron’s have the same 4
quantum numbers
• One electron will spin up, the other will
spin down
• Conventionally we write the electron that
spins up first.
Aufbau Principle
• The number of electrons in an atom is equal to
the atomic number
• Each added electron will enter the orbitals in the
order of increasing energy
• Orbitals of lowest energy are filled first
• An orbital cannot take more than 2 electrons.
• Analogy: You’re very tired after a night out. It’s
easier to sleep downstairs on the couch than to
climb the stairs to your bedroom. If your friend is
already sleeping on the couch, then you will go
upstairs.
Aufbau Principle
Hund’s Rule
• Every orbital in a subshell is singly
occupied with one electron before any one
orbital is doubly occupied
• All electrons in singly occupied orbitals
have the same spin.
• Analogy: When boarding the bus, you
would take an empty seat rather than sit
beside someone.
• Lithium
• Nitrogen
• Manganese
Examples
Electron Configuration for Ions
• For anions: add extra electrons
• For cations: draw the neutral atom, then
subtract the required number of electrons
from the orbital with the highest principal
quantum number “n”
• Examples S2-, Na+, Zn2+
Practice
• Activity
• P. 191 #1-5
• P. 194 #6-11
Electron Configuration:
Finding Trends
Group Group Group Group Group Group Group Group
1
2
13
14
15
16
17
18
In a chart, write condensed electron configurations and energy
level diagrams for the elements in periods 2 and 3.
What patterns do you notice? What generalizations can you
make?