Unit 4 - Electrons in Atoms
Electron
Configuration
Atomic Model Review
Bohr – Electrons are found in
orbitals around the nucleus
De Broglie – Electrons behave
like waves
Consensus – Electrons are found
in clouds around the nucleus
Quantum Model
There are several energy levels
occupied by electrons
Energy levels are represented by
a positive integer
As the distance from the nucleus
increases, the number increases
Quantum Model
n=3
n=2
n=1
Nucleus
Quantum Model
There are several types of orbitals
that can occur in an energy level
Orbitals have a specific shape and
are represented by a lowercase
letter
Quantum Model
s-orbital – SPHERICAL – 1 orbital
Quantum Model
p-orbital – BOWTIE – 3 orbitals
Quantum Model
d-orbital – CLOVERLEAF – 5
orbitals
Quantum Model
f-orbital – COMPLICATED!  – 7
orbitals
Quantum Model
Different energy levels have
different types of orbitals.
1st energy level - s orbital
2nd energy level – s & p orbitals
3rd energy level – s, p, & d orbitals
4th energy level – s, p, d, & f orbitals
Quantum Model – Hog Hilton
3p ___ ___ ___
3s ___
2p ___ ___ ___
2s ___
1s ___
I KNOW HOW MANY
ELECTRONS AN ATOM HAS…
BUT HOW DO THE
ELECTRONS FIT INTO THE
ORBITALS??
General Rules
Pauli Exclusion Principle
Each orbital can hold TWO
electrons with opposite spins.
General Rules
Aufbau Principle
Electrons fill the
lowest energy
orbitals first.
“Lazy Tenant
Rule”
Aufbau Principle
General Rules
Hund’s Rule
Within a sublevel, place one eper orbital before pairing them.
“Empty Bus Seat Rule”
WRONG
RIGHT
Notation
Orbital Diagram
O
8e-
1s
2s
Electron Configuration
2
2
4
1s 2s 2p
2p
Practice…
Helium (He)
Carbon (C)
Sodium (Na)
Phosphorus (P)
Nitrogen (N)
Aluminum (Al)
Calcium (Ca)
Argon (Ar)
Notation
There’s an easier way to figure
out electron configurations
We can use our handy-dandy,
trusty periodic table
Periodic Patterns
s
p
1
2
3
4
5
6
7
d
f
6
7
© 1998 by Harcourt Brace & Company
C. Periodic Patterns
Example - Hydrogen
1
2
3
4
5
6
7
1
1s
1st Period
1st column
of s-block
s-block
Use the periodic table…
Helium (He)
Carbon (C)
Sodium (Na)
Phosphorus (P)
Iron (Fe)
Zirconium (Zr)
Calcium (Ca)
Iodine (I)
Notation – A Shorter Way!
Noble gas – column on the far right
of the periodic table
Last energy level is full of electrons
Like a full floor of the Hog Hilton
Examples
He – 1s2
Ar – 1s2 2s2 2p6 3s2 3p6
Notation
We can abbreviate the full energy
levels by using noble gases
Example - Sulfur
Notation
Longhand Configuration
S 16e- 1s2 2s2 2p6 3s2 3p4
Shorthand Configuration
S
16e
2
4
[Ne] 3s 3p
Shorthand Notation
Example - Germanium
1
2
3
4
5
6
7
[Ar]
2
4s
10
3d
2
4p
Shorthand Notation
Sulfur (S)
Tin (Sn)
Barium (Ba)
Silver (Ag)
Valence Electrons
The electrons found in the
outermost shell or level
S
16e
1s2
Core Electrons
6
2
2s 2p 3s2 3p4
Valence Electrons
Periodic Table Patterns
Period # (Row #) = Energy Level
 Subtract 1 for d
 Subtract 2 for f
Group # (Column #) = Total # of
valence electrons
 True for s & p block
 d & f blocks are weird… 
Lewis Dot Diagrams
Represents the number and
placement of valence electrons in
an atom
Lewis Dot Diagrams
Remember your electron rules
Be single before you double!
Electrons want to be far apart!
Since we’re only looking at the s
& p blocks, the total number will be
8 or less (except H & He)
Lewis Dot Diagrams
Example – OXYGEN
How many valence electrons?
Write the element symbol
Fill in the dots
Stability
Full energy level
Full orbital (s, d, f)
Half-full orbital (p, d, f)
1
2
3
4
5
6
7
Stability
Electron Configuration Exceptions
Copper
EXPECT:
[Ar] 4s2 3d9
ACTUALLY:
[Ar] 4s1 3d10
Copper gains stability with a full
d-orbital.
Stability
Electron Configuration Exceptions
Chromium
EXPECT:
[Ar] 4s2 3d4
ACTUALLY:
[Ar] 4s1 3d5
Chromium gains stability with a half-full
d-orbital.
Stability – Ion Formation
Ion = charged atom; not neutral
Atoms gain or lose electrons to become
more stable
More stable = noble gas configuration
1
2
3
4
5
6
7
Stability
Ion Electron Configuration
Write the e- config for the Noble
Gas that the ion wants to “become”
EX: Oxygen ion  O2Oxygen (8) wants to be Neon (10)
O2-
10e-
[He] 2s2 2p6
Ground State
Energy level that an electron
normally occupies
State of lowest energy for an electron
Hogs are lazy & don’t like to climb
stairs
Ground State
When an electron temporarily occupies
an energy level GREATER than its
ground state, it is in an EXCITED state
Excitement occurs when an electron
absorbs a photon (light emitting
particle)
So when an electron RETURNS to its
ground state, it will emit a PHOTON
Ground State  Excited State
Excited State  Ground State
Here’s the cool part!
The color of the emitted light
depends on the amount of energy in
the photon!
Electromagnetic Spectrum
Amount of energy depends on
wavelength
Flame Test
Can be used to identify unknown metals