Quantum Numbers
Describes the arrangement of
electrons in atoms in terms of:
energy levels, size
Pathway of travel
Direction of rotation
Principal Quantum number (n)

Contain electrons that are similar in
energy and distance from nucleus

Low energy electrons are closest to the
nucleus

Identify by numbers 1, 2, 3, 4, 5, 6…..

The first shell (1) is lowest in energy,
2nd level next and so on 1<2<3<4
Number of Electrons
Maximum number of electrons in
any electron energy level = 2n2
n =1
n =2
n =3
2(1)2
2(2)2
2(3)2
=
=
2
8
=
18
Orbital Quantum number

Indicates the pathway of travel

Electrons move in different paths
due to their negative charge.

Designated s, p, d, f ..

Sublevel energy: s<p<d<f
Magnetic Quantum number
 Orientation
of path
 Direction of movement with respect
to the nucleus
S orbitals
1 s orbital for
every
energy
level
 Spherical
shaped
 Each s orbital can hold 2 electrons
 Called the
1s
2s
3s etc..
orbitals.

P orbitals



3 different directions
3 identical shapes
Each can hold 2 electrons
P Orbitals put together
D orbitals
Higher in energy than s or p due to
advanced shape
 5 shapes, 4 are identical

F orbitals
More complex still
Have seven different shapes
F orbitals

More complex still
Spin Quantum number
Describes rotation of electron in an
orbital
 Either clockwise (+1/2) or
 Counter clockwise (-1/2)

Summary
Seven energy levels (n=1,2,3,4…)
 Four pathways (s,p,d,f)
 Orientations: s=1, p=3, d=5, f=7
 Two spins in each orbital
 Maximum electrons are: s=2, p=6,
d=10, f=14

Summary
# of
shapes/
orbitals
Max #
electrons/
orbital
Starts at
energy level
s
1
2
1
p
3
6
2
d
5
10
3
f
7
14
4
By Energy Level
First Energy Level
 only s orbital
 only 2 electrons
2
 1s

Second Energy
Level
 s and p orbitals
are available
 2 in s, 6 in p
 2s22p6
 8 total electrons

By Energy Level
Third energy level
 s, p, and d
orbitals
 2 in s, 6 in p, and
10 in d
 3s23p63d10
 18 total electrons

Fourth energy
level
 s,p,d, and f
orbitals
 2 in s, 6 in p, 10
in d, ahd 14 in f
2 6 10 14
 4s 4p 4d 4f
 32 total electrons

By Energy Level
Any more than
the fourth and not
all the orbitals will
fill up.
 You simply run
out of electrons

The orbitals do
not fill up in a
neat order.
 The energy levels
overlap
 Lowest energy fill
first.

Electron Locations
Main
Energy
Levels
n=4
Sublevels
4s, 4p, 4d, 4f
n=3
3s, 3p, 3d
n=2
2s, 2p
n=1
1s
Sublevels in n = 1,2, 3
n=3
3d
3p
3s
n=2
2p
2s
n=1
1s
Electrons Allowed


All electrons in the same sublevel have the
same energy.
All 2s electrons have the same energy. All 2p
electrons, the same energy which is slightly
higher than that of the 2s electrons
s sublevel
2 electrons
p sublevel
6 electrons
d sublevel
10 electrons
f sublevel
14 electrons
Increasing energy
7s
6s
5s
7p
6p
5p
4p
4s
3p
3s
2p
2s
1s
6d
5d
4d
3d
5f
4f
Electron Configurations
List of subshells containing
electrons
 Written in order of increasing
energy
 Superscripts give the number of
electrons

Electron Configuration
Example: Neon
number of electrons
1s2
main shell
2s2
2p6
subshell
Electron Configurations
The way electrons are arranged in
atoms.
 Aufbau principle- electrons enter the
lowest energy first.
 This causes difficulties because of the
overlap of orbitals of different energies.
 Pauli Exclusion Principle- at most 2
electrons per orbital - different spins

Electron Configuration
Hund’s Rule- When electrons occupy
orbitals of equal energy they don’t
pair up until they have to .
 Let’s determine the electron
configuration for Phosporus
 Need to account for 15 electrons

Increasing energy
7s
6s
5s
7p
6p
6d
5d
5p
4d
4p
3d
4s
3p
3s
2s
1s
The first to electrons
go into the 1s orbital
2p
 Notice the opposite
spins
 only 13 more

5f
4f
Increasing energy
7s
6s
5s
7p
6p
6d
5d
5p
4d
4p
3d
4s
3p
3s
2s
1s
The next electrons
go into the 2s orbital
2p
 only 11 more

5f
4f
Increasing energy
7s
6s
5s
4s
3s
2s
1s
7p
6p
5p
4p
6d
5d
4d
3d
3p • The next electrons go
into the 2p orbital
2p
• only 5 more
5f
4f
Increasing energy
7s
6s
5s
4s
3s
2s
1s
7p
6p
5p
4p
6d
5d
4d
3d
3p • The next electrons go
into the 3s orbital
2p
• only 3 more
5f
4f
Increasing energy
7s
6s
5s
4s
7p
6p
6d
5d
5p
4d
4p
3p •
3s
2s
1s
2p •
•
•
5f
4f
3d
The last three electrons
go into the 3p orbitals.
They each go into
seperate shapes
3 upaired electrons
1s22s22p63s23p3
The easy way to remember
7s 7p 7d 7f
6s 6p 6d 6f
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s
•
2
1s
• 2 electrons
Fill from the bottom up
following the arrows
7s 7p 7d 7f
6s 6p 6d 6f
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s
•
2
2
1s 2s
• 4 electrons
Fill from the bottom up
following the arrows
7s 7p 7d 7f
6s 6p 6d 6f
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s
•
2
2
6
2
1s 2s 2p 3s
• 12 electrons
Fill from the bottom up
following the arrows
7s 7p 7d 7f
6s 6p 6d 6f
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s
•
2
2
6
2
1s 2s 2p 3s
6
2
3p 4s
• 20 electrons
Fill from the bottom up
following the arrows
7s 7p 7d 7f
6s 6p 6d 6f
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s
•
2
2
6
2
1s 2s 2p 3s
6
2
10
6
3p 4s 3d 4p
5s2
• 38 electrons
Fill from the bottom up
following the arrows
7s 7p 7d 7f
6s 6p 6d 6f
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s
•
2
2
6
2
1s 2s 2p 3s
6
2
10
6
3p 4s 3d 4p
5s2 4d10 5p6 6s2
• 56 electrons
Fill from the bottom up
following the arrows
7s 7p 7d 7f
6s 6p 6d 6f
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s
•
2
2
6
2
1s 2s 2p 3s
6
2
10
6
3p 4s 3d 4p
5s2 4d10 5p6 6s2
4f14 5d10 6p6 7s2
• 88 electrons
Fill from the bottom up
following the arrows
7s 7p 7d 7f
6s 6p 6d 6f
5s 5p 5d 5f
4s 4p 4d 4f
3s 3p 3d
2s 2p
1s
•
2
2
6
2
1s 2s 2p 3s
6
2
10
6
3p 4s 3d 4p
5s2 4d10 5p6 6s2
4f14 5d10 6p6 7s2
5f14 6d10 7p6
• 108 electrons
Writing Electron Configurations
H
1s1
He
1s2
Li
1s2 2s1
C
1s2 2s2 2p2
S
1s2 2s2 2p6 3s2 3p4
Periodic Table and Electron
Configuration
Find element on the periodic table
 Use the order of filling indicated
across each period
Groups 1-2
= ns level
Groups 3-8
= np level
Transition
= (n-1)d level
Lanthanides
= (n-2)f level

Exceptions to Electron
Configuration
Orbitals fill in order
Lowest energy to higher energy.
 Adding electrons can change the
energy of the orbital.
 Half filled orbitals have a lower
energy.
 Makes them more stable.
 Changes the filling order

Write these electron
configurations
Titanium - 22 electrons
 1s22s22p63s23p64s23d2
 Vanadium - 23 electrons
1s22s22p63s23p64s23d3
 Chromium - 24 electrons
 1s22s22p63s23p64s23d4 is expected
 But this is wrong!!

Chromium is actually
1s22s22p63s23p64s13d5
 Why?
 This gives us two half filled orbitals.
 Slightly lower in energy.
 The same principal applies to copper.
 Write the Cu configuration now

Copper’s electron
configuration
Copper has 29 electrons so we
expect
 1s22s22p63s23p64s23d9
 But the actual configuration is
 1s22s22p63s23p64s13d10
 This gives one filled orbital and one
half filled orbital.
 Remember these exceptions

Orbital Notation

A 3 dimensional space around a nucleus
in which electrons are most likely to be
found

Shape represents electron density (not a
path the electron follows)

Each orbital can hold up to 2 electrons.
Learning Check S5
A. Number of electrons in a p orbital
1) 1e
2) 1e or 2e
3) 3e
B. Number of orbitals in a p subshell
1) 1
2) 2
3) 3
C. Number of orbitals in 4d subshell
1) 1
2) 3
3) 5
D. Number of electrons (maximum) in a 3d
1) 2e
2) 5e
3) 10e
Solution S5
A. Number of electrons in a p orbital
2) 1e or 2e
B. Number of orbitals in a p subshell
3) 3
C. Number of orbitals in 4d subshell
3) 5
D. Number of electrons in a 3d subshell
3) 10e
The Periodic Law
All the elements in a group have the
same electron configuration in their
outermost shells
Example:
Group 2
Be 2, 2
Mg 2, 8, 2
Ca 2, 2, 8, 2
Learning Check EA5
Specify if each pair has chemical
properties that are similar (1) or not (2):
A. Cl and Br
B. 2 - 5 and 2 - 8 - 7
C. 2 - 4 and 2 - 8 - 4
D. P and S
E. O and S
Solution EA5
Specify if each pair has chem. properties
that are similar (1) or not similar (2):
A. Cl and Br
1
B. 2 - 5 and 2 - 8 - 7
2
C. 2 - 4 and 2 - 8 - 4
1
D. P and S
2
E. O and S
1
Learning Check S2
Indicate if each configuration is (1) correct
or (2) incorrect for potassium. Give an
explanation for selection of 1 or 2. Explain
A.
B.
1s22s22p63s1
1s22s22p63s23p6
1 or 2
1 or 2
C.
1s22s22p63s23p64s1
1 or 2
D.
1s22p83s1
1 or 2
E.
1s22s22p63s23p7
1 or 2
Solution E2
For phosphorus, indicate if each
configuration is (1) correct or (2)
incorrect. Explain why or why not.
A. 2, 2, 8, 5
2
B. 2, 8, 3
2
C. 2, 8, 5
1
D. 2, 6, 7
2
Learning Check S3
Using the periodic table, write the complete
electronic configuration for each:
A. Cl
B. Sr
C. I
Solution S3
Using the periodic table, write the complete
electronic configuration for each:
A. Cl
1s2 2s2 2p6 3s2 3p5
B. Sr
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2
C. I
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p5
Learning Check S4
A.
The final two notations for Co are
1) 3p64s2
2) 4s24d7
3) 4s23d7
B. The final three notations for Sn are
1) 5s25p24d10
2) 5s24d105p2
3) 5s25d105p2
Solution S4
A.
The final two notations for Co are
3) 4s2 3d7
B. The final three notations for Sn are
2) 5s2 4d10 5p2