The Modern Atomic Theory:
A Closer Look at the Electron
Blocks in The Periodic Table
Row #
1
2
3
4
5
6
7
= s block
= p block
= d block
= f block
Where is the Electron?
• In the quantum mechanical model, the
electrons are found outside the nucleus.
• To describe an electron’s location, we can
includes
1. Its Energy Level
2. Its Sublevel
3. Its Atomic Orbital
Principle Energy Levels
• The first horizontal row of the periodic table represents
the first or (n=1) principle energy level.
• Represented by the letter, n
n = 1  First Energy Level
• Each new row on the periodic table starts a new energy
level.
• Each energy level has a different number of sublevels, a
different number of orbitals, and a different number of
electrons.
The Bohr Model
Sublevels
• Based on the number of elements in our
Periodic Table, there are four sublevels.
s, p, d, f
• Each sublevel has a unique shape.
• The size of the sublevel depends on the
energy level.
Higher Energy Level = Bigger Sublevel
s-Sublevel
sphere
p-Sublevel
dumb bell
This is only one
of the p-sublevel
atomic orbitals.
Since there are 3 orbitals in the pSublevel:
d-Sublevel
Don’t need to memorize these!
f- Sublevel
Don’t need to memorize these!
Summary of the Sublevels
Sublevel
Number of
Atomic Orbitals
Maximum
Number of
Electrons
s
1
2
p
3
6
d
5
10
f
7
14
Atomic Orbitals
• All electrons are located in an atomic orbital or
orbital.
• An atomic orbital represents the area in which
there is a 90% chance of finding an electron.
• Each atomic orbital can hold two electrons.
• Inside these orbitals, electrons take random
and unpredictable paths.
Processing Your Notes
Question #1
1. Which sublevel has a dumbbell shape?
a) s sublevel
The p-sublevel
b) p sublevel
has a dumbbell
c) d sublevel
shape, while the
d) f sublevel
s-sublevel has a
spherical shape.
Processing Your Notes
Question #2
2. Which sublevels will have the same
shape?
a) 3s and 3p
The letter or
b) 3p and 4p
sublevel
determines the
c) 1s and 2p
shape.
d) 4d and 3s
Processing Your Notes
Question #3
3. Sodium is found on the third row or Period
3 of the periodic table. How many energy
levels do the electrons of a sodium atom
occupy?
a) 1
b) 3
3rd Row = 3 Energy Levels
c) 11
d) 23
Processing Your Notes
Question #4
4. How many orbitals are found in a dsublevel?
Be Careful!
a) 4
The d-sublevel has
b) 5
5 orbitals and holds
10 electrons.
c) 10
You will want to
d) 14
memorize that
table!
Processing Your Notes
Question #5
5. How many electrons can be held in one
atomic orbital?
a) 2
b) 6
c) 10
d) 14
Processing Your Notes
Question #6
6. Which letter does not represent a current
sublevel of an energy level?
a) d
n represents the
b) f
energy level not a
c) n
sublevel.
d) p
Processing Your Notes
Question #7
7. As scientists create new elements, we will need to add
new sublevels to the four existing sublevels. In fact, the
next sublevel will be called g. After looking at the trend in
the number of orbitals for the current sublevels, how
many orbitals would you predict would exist in a gsublevel?
a) 7
s =1
b) 8
p=3
c) 9
d =5
d) 32
f =7
g=9
Putting It All Together
1
2
3
4
s
s&p
s, p, & d
1
4
9
16
2
8
18
32
s, p, d, & f
Electron Configurations
Electron Configurations represent the location
of the electrons in an atom or ion.
the number
of electrons
2
2
5
1s 2s 2p
the energy
level of the
electron (n)
the sublevel
Processing Your Notes
Question #8
8. How many orbitals are in the fourth
energy level?
For the fourth energy,
a) 4
you have s, p, d and f.
b) 8
s = 1 orbital
p = 3 orbitals
c) 16
d
=
5
orbitals
d) 32
f = 7 orbtials
Add these up!
1 + 3 + 5 +7 = 16
Processing Your Notes
Question #9
9. How many electrons are held in n=2?
a) 2
n=2 means the second
b) 4
energy level.
c) 8
s = 2 electrons
p = 6 electrons
d) 16
Add these up!
2 + 6 = 8 electrons
Processing Your Notes
Question #10
10. Which of the following sublevels does
not exist?
• On the first energy level, you only
a) 1s
have 1s.
• On the second energy level, you
b) 2d
only have 2s and 2p.
c) 3p
• On the third energy level, you only
have 3s, 3p, and 3d.
d) 4f
• All four sublevels are on the fourth
energy level.
Processing Your Notes
Question #11
11. Which of the following would be an
expression used to calculate the number of
orbitals based on the energy level (n)?
a) 2n
2 = 1
n
=
1
n
b) n2
n=2
n2 = 4
c) n + 6
n=3
n2 = 9
2 = 16
2
n
=
4
n
d) 2n
Processing Your Notes
Question #12
1s22s22p63s23p4
12. Which element is represented by this
electron configuration?
a) sodium
Add up the
exponents!
b) sulfur
c) argon
Since it is neutral,
d) selenium
protons = electrons.
Processing Your Notes
Question #13
1s22s22p63s23p4
13. What is the highest energy level in this
electron configuration?
a) 2
Energy level
represented by the
b) 3
coefficient
or
the
big
c) 4
number.
d) 6
Processing Your Notes
Question #14
1s22s22p63s23p4
14. How many electrons are found in the ssublevel?
a) 2
b) 4
2+2+2=6
c) 6
d) 8
Processing Your Notes
Question #15
1s22s22p63s23p64s23d104p1
15. Which sublevel has the most electrons?
a) s
b) p
p = 13 electrons
d = 10 electrons
c) d
s = 8 electrons
d) f
Processing Your Notes
Question #16
1s22s22p63s23p64s23d104p1
16. How many electrons are in the highest
energy level?
a) 1
The “coefficient”
determines the
b) 2
energy,
so
4s
and
4p
c) 3
are both on the
d) 13
highest energy level.
Processing Your Notes
Question #17
1s22s22p63s23p64s23d104p1
17. What element is represented by the
electron configuration?
a) titanium
Add up the
exponents!
b) copper
c) gallium
Since it is neutral,
d) germanium
protons = electrons.
Rule #1: Pauli’s Exclusion Principle
Each atomic orbital can hold two
electrons.
Sublevel
# of Orbitals
Max # of
Electrons
s
p
d
f
1
3
5
7
2
6
10
14
Rule #2: Aufbau Principle
Electrons will fill the atomic orbital
with the lowest energy first.
2
2
6
2
6
2
10
5
1s 2s 2p 3s 3p 4s 3d 4p
Lowest Energy  Highest Energy
Blocks in The Periodic Table
Row #
1
2
3
4
5
6
7
= s block
= p block
= d block
= f block
Sample Electron Configurations
• Hydrogen  1s1
• Beryllium  1s22s2
• Fluorine  1s22s22p5
• Chlorine  1s22s22p63s23p5
• Potassium  1s22s22p63s23p64s1
Important Reminders
• Your row number tells you the energy level or
coefficient for your configurations.
• Know your limits for each sublevel!
• You have to use your periodic table be sure
that you are following the Aufbau Principle.
1s  2s  2p  3s  3p  3d
X
1s  2s  2p  3s  3p  4s
Electron Configurations
(Containing the d-Sublevel)
The energy level of d-sublevel will
ALWAYS be one less than the row
or period number.
Blocks in The Periodic Table
Row #
1
2
3
4
5
6
7
= s block
= p block
row # -1
= d block
= f block
Sample Electron Configurations
• Titanium
• Iron
1s22s22p63s23p64s23d2
1s22s22p63s23p64s23d6
• Bromine
1s22s22p63s23p64s23d104p5
• Tellurium
• Silver
1s22s22p63s23p64s23d104p65s24d105p4
1s22s22p63s23p64s23d104p65s24d9
Where does the f-block “fit in”?
The f-block is considered to
be part of periods 6 and 7.
Electron Configurations
(Containing the f-Sublevel)
The energy level of f-sublevel will
ALWAYS be two less than the row
number.
Blocks in The Periodic Table
= s block
= p block
Row #
1
2
= d block
= f block
row # -1
3
4
5
6
7
6
7
row # -2
Sample Electron Configurations
• Europium
1s22s22p63s23p64s23d104p65s24d105p66s25d14f6
• Tungsten
1s22s22p63s23p64s23d104p65s24d105p66s25d14f145d3
• Bismuth
1s22s22p63s23p64s23d104p65s24d105p66s25d14f145d96p3
• Bohrium
1s22s22p63s23p64s23d104p65s24d105p66s25d14f145d96p67s26d15f146d4
Exceptions to the Rules
Make sure you know these!!
Chromium, Cr
Predicted: 1s22s22p63s23p64s23d4
Actual: 1s22s22p63s23p64s13d5
Copper, Cu
Predicted: 1s22s22p63s23p64s23d9
Actual: 1s22s22p63s23p64s13d10
Short-Hand Notation
[Ne]3s23p2
Uses a noble gas
(Group 18) to
represent the
innermost electrons.
Outermost
electrons are
represented the
same way.
Noble Gases = He, Ne, Ar, Kr, Xe, Rn
Short Hand Notation Hints
•To find the noble gas, look at the noble
gas from the previous row or the row
above the element.
• The energy level or coefficient of the s
and p-sublevel is equal to the row or
period number.
• The energy level or coefficient of
the d-sublevel is one less than the
period number and for the f-sublevel
two less than the period number.
Sample Electron Configurations
• Nickel, Ni
[Ar]4s23d8
• Antimony, Sb
[Kr]5s24d105p3
• Lead, Pb
[Xe]6s25d14f145d96p2
Then combine your d’s!
[Xe]6s24f145d106p2
Valence Electrons:
Valence Electrons are the electrons in the _______________________ energy
level.
The energy levels below have the _______________ number of electrons allowed.
The number of electrons in the outer level can be found by looking at the
highest energy level in the ________________ ____________________ or
by looking at the __________________ __________________ located
above the column where the element is _________________________.
Examples:
Mg= Group ___ A so it has _____ valence electrons.
Pb= Group ____ A so it has _____ valence electrons.
Label the Valence Electrons for each Column on the Periodic Table
Label the Valence Electrons for each Column on the Periodic Table
Draw the Lewis Dot Diagrams for the following
elements:
Sodium
Magnesium
Aluminum
Silicon
Chlorine
Phosphorus
Argon
Sulfur
Valence Electrons
Electrons in the highest energy level.
1s22s22p63s23p2
• What is the highest energy level?
n =3 or third energy level
• How many electrons are on the highest
energy level?
4 electrons
• How many valence electrons are in this
element?
4 electrons
Lewis Dot Diagrams
Element
Symbol
One Dot for
Each Valence
Electron
How Are the Dots Arranged?
4
7
3
8
X
6
2
1
5
Example Dot Diagrams
Write the electron configuration and
draw the dot diagrams for each of the
following elements.
•Helium
He
•Carbon
C
F
•Neon
Ne
Short Cut for Valence Electrons
13
IIIA
5
B
Boron
13
Al
Aluminum
31
Ga
Gallium
Use the
group
number!
All of the elements in Group
13 or IIIA will have three
valence electrons.
Using the Short Cut
Using the short cut, determine the
number of valence electrons.
–Phosphorus
–Argon
–Lead
–Barium
5 valence electrons
8 valence electrons
4 valence electrons
2 valence electrons
Exceptions to the Short Cut
• Only works for Group A Elements
or the Representative Elements
s and p-blocks ONLY
• Helium  two valence electrons
Write the electron configuration and
draw the Lewis dot diagram for
lithium, sodium, and potassium.
The arrangement of electrons helps explains the world around us.
In this case, all of the Group 1 elements have similar electron
configurations, and therefore, have similar chemical properties.
Alkali Metals in Water
Rule #1: Pauli’s Exclusion Principle
Each atomic orbital can hold two
electrons with opposite spins.
Rule #2: Aufbau Principle
Electrons will fill the atomic orbital
with the lowest energy first.
2
2
6
2
6
2
10
5
1s 2s 2p 3s 3p 4s 3d 4p
Lowest Energy  Highest Energy
Rule #3: Hund’s Rule
When filling equal energy orbitals,
electrons will arrange themselves to
maximize unpaired electrons.
Equal energy orbitals are
orbitals in the same
sublevel.
Orbital Diagrams
1s
2s
2p
1 box = 1 atomic orbital
s-sublevel  1 box
p-sublevel  3 boxes
d-sublevel  5 boxes
f-sublevel  7 boxes
1 arrow = 1 electron
3s