Honors Chemistry
Section 4.3
Electron Configurations
Electron Configuration is the arrangement
of electrons in an atom
 Every atom has a unique electron
configuration
 Atoms tend to lowest E state, so normally
exist in ground state

Electron Configuration
Aufbau Principle – Electrons occupy the
lowest energy orbital available to them
 Pauli Exclusion Principle – No two
electrons can have the same 4 quantum
numbers
 Hund’s Rule – Orbitals of equal energy
(called degenerate orbitals) are each
occupied by one electron, before any is
occupied by a second electron. All single
electrons have the same spin.

Rules for Electron Configuration
Orbital Energies

Hydrogen
◦

Helium
◦

↿
1s
↿⇂
1s
Oxygen
◦ ↿⇂
1s
↿⇂
2s
↿⇂ ↿⇂ ↿⇂
2px 2py 2pz
Orbital Notation

Hydrogen
◦ 1s1

Helium
◦ 1s2

Oxygen
◦ 1s2 2s2 2p4
Electron Configuration
Filling Order – Memory Aid

What is the electron configuration of
Carbon?

Write the electron configuration and
orbital notation for Sulfur
Practice




Highest Occupied Level – The highest main
energy level (highest n value) that contains
an electron
Outer shell electrons – electrons in the
Highest Occupied Level
Inner shell electrons – all those electrons
EXCEPT those in the Highest Occupied Level
Example – Carbon
◦ 2 inner shell electrons
◦ 4 outer shell electrons
Definitions
Noble gas – Has full s and p orbitals
 Noble gas configuration

◦ [symbol] stand for the complete electron
configuration of the specified noble gas
◦ Add electrons after noble gas required for
element.
◦ Na – [Ne] 3s1
Noble Gases

All noble gases have full outer main
energy levels
◦ He – 2 electrons (Energy Level n=1)
◦ All others – 8 electrons (Energy Level n = 2 to
7)
Important Note
Filling Orbtials and the Periodic
Table
Fill 4s first
 Then next lowest energy 3d – it fills next
 Followed by 4p

Fourth Period

Chromium
◦ Expected - [Ar] 3d4 4s2
◦ Actual - [Ar] 3d5 4s1
◦ Why?
 Two half filled orbitals have more stability and lower
energy than one full and one partially full

Copper
◦ Expected - [Ar] 3d8 4s2
◦ Actual - [Ar] 3d10 4s0
◦ Why?
 A full d orbital and unfilled s orbital have more stability
and lower energy than one full and one partially full
4th Period Exceptions to the
Expected Filling Order – KNOW
THESE!!!!

Deviates from Nb to Ag
5th Block Exceptions to the
Expected Filling Order
1.
What element has 2 electrons in the p
orbitals in the 2nd Energy Level?
2.
What is the maximum number of
electrons that can be found on the
second energy level?
3.
What element in the third period has the
same outer electron configuration as the
element in #1?
Practice
1.
What element has 5 electrons in the p
sublevel on the third energy level?
2.
How many total electrons does this
element have on the third energy level?
3.
What element in the 4th Period has the
same outer configuration as this
element?
More Practice

What element has the configuration
[Ne]3s1?

How many inner shell electrons does this
element have?

What is the Noble Gas configuration for
Al?
◦ How many outer shell electrons?
◦ How many inner shell electrons?
Even More Practice

Write the electron configuration and Noble
Gas configuration for Ti.

How many electron containing orbitals in
Ti?

How many orbitals in Ti are completely
filled?
Are you Ready for More?