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QUANTUM NUMBERS
&
ELECTRON
CONFIGURATION
General Chemistry I
1
QUANTUM MODEL
QUANTUM THEORY
Describes mathematically the wave
properties of electrons and other very small
particles
QUANTUM MECHANICAL MODEL
Electrons are treated as waves and makes
no attempt to describe electron’s path
Calculated the probability of finding the
electron within a volume of space around
the nucleus
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QUANTUM MECHANICAL MODEL
90%
Probability
of finding
electrons
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Probability Distribution
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Probability Distribution
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QUANTUM NUMBERS
Numbers that describe the energies of
electrons in atoms
Specify the properties of atomic
orbitals and the properties of electrons
in orbitals
Think of the quantum numbers as
addresses for electrons
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FOUR QUANTUM NUMBERS
Principal Quantum Number (n)
Angular Momentum Quantum
Number (l )
Magnetic Quantum Number (ml)
Spin Quantum Number (s )
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PRINCIPAL QUANTUM NUMBER
Electron Cloud Size (n)
Indicates the main energy level
occupied by the electron
Can take on integer values
n = 1, 2, 3,…. 
Largely determine the energy of the
orbital (bigger n value = higher
energy)
All electrons in an atom with the same
value of n belong to the same shell
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PRINCIPAL QUANTUM NUMBER . . .
Spectroscopists use
the following names
for shell
Shell
n
Name
n
Shell
Name
1
K
5
O
2
L
6
P
3
M
7
Q
4
N
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ANGULAR MOMENTUM
QUANTUM NUMBER
Shape of Electron Cloud (l)
Also known as sublevel or subshell
Indicates the shape of the orbital within a shell
Only integer values between 0 and n-1 are
allowed
Affects orbital energies (bigger l = higher energy)
All electrons in an atom with the same value of l
are said to belong to the same subshell
Sometimes called the orbital azimuthal quantum
number
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ANGULAR MOMENTUM
QUANTUM NUMBER . . .
Spectroscopists use the following
notation for subshells
l
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Subshell Name
0
s (sharp)
1
p (principal)
2
d (diffuse)
3
f (fundamental)
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MAGNETIC QUANTUM
NUMBER
Orientation in space of orbitals (ml)
Determines the orientation of orbitals
within a subshell
Does not affect orbital energy (except in
magnetic fields!)
Only integer values between –l and +l are
allowed
The number of ml values within a subshell
is the number of orbitals within a subshell
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MAGNETIC QUANTUM
NUMBER . . .
Number of ml values determines the
number of orbitals in a subshell
l
0 (s)
1 (p)
2 (d)
3 (f)
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Possible values of ml
# orbitals in the
subshell
0
1
-1 , 0 ,+1
3
-2, -1, 0, +1, +2
5
-3, -2, -1, 0, +1,+2,+3
7
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SPIN QUANTUM NUMBER
Direction of spin (s)
Spin makes the electron behave like
tiny magnets
Spin can be clockwise or
counterclockwise
Spin quantum numbers can have
values of +½ or -½
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SPIN QUANTUM NUMBER
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Quantum Numbers &
Atomic Structure
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ATOMIC ORBITALS
Region in space where there is a
high probability of finding an
electron
Shapes
s – spherical
p – dumbbell-shaped
d & f – complex shapes
Special People Don’t Forget 1, 3, 5, 7
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ATOMIC ORBITALS
(s-orbital)
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ATOMIC ORBITALS (p-orbital)
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ATOMIC ORBITALS
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ATOMIC ORBITALS
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ATOMIC ORBITALS
f - orbitals
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ELECTRON CONFIGURATION
An arrangement of electrons in an atom
GROUND STATE – the lowest energy
state of an atom
EXCITED STATE – a state in which an
atom has a higher potential energy
DEGENERATE ORBITALS – two or more
orbitals that have the same energy (p, d, f)
ELECTRON ARRANGEMENT DETERMINES THE CHEMICAL BEHAVIOR
OF ATOMS
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ELECTRON CONFIGURATION
(RULES)
AUFBAU
PRINCIPLE
Electrons enter
atomic orbitals of
lower energy
first
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Aufbau Principle
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Diagonal Diagram
1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s
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PAULI EXCLUSION PRINCIPLE
No two electrons can have the
same set of quantum numbers
An atomic orbital contains a
maximum of two electrons
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HUND’S RULE
Orbitals of equal energy are each
occupied by one electron before
any orbital is occupied by a second
electron
Electrons in singly occupied
orbitals must have the same spins
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Representing
Electron Configurations
ORBITAL NOTATION –orbital is
represented by a line, with the orbital’s
name written under the line and the
electrons are represented by arrows.
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Electron Configuration &
Periodic Table
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OUTERMOST SUBLEVEL
BEING FILLED
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Representing
Electron Configurations
ELECTRON CONFIGURATION NOTATION
Carbon: 1s22s22p2
HIGHEST OCCUPIED LEVEL
Electron-containing main energy level with the
highest principal quantum number
VALENCE ELECTRONS
Electrons in the highest occupied main energy level
INNER SHELL (CORE) ELECTRONS
Electrons that are not in the highest occupied
energy level
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Inner Core & Valence
Electrons
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Representing
Electron Configurations
NOBLE GAS NOTATION
Na: [Ne]3s1
P: [Ne]3s23p3
Noble Gas Configuration
An outer main energy level fully
occupied, in most cases, by eight
electrons (octet)
Ne: 1s22s22p6
Ar: [Ne] 3s23p6
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Noble Gas Notation
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Outer Electron Config.
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Electron Dot Notation
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EXCEPTIONS TO RULES
Half filled orbitals - Cr24
1s22s22p63s23p6 4s2 3d4
] [[[[p
Stable configuration is
1s22s22p63s23p6 4s1 3d5
[ [[[[[
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EXCEPTIONS TO RULES
Filled Orbitals - Cu29
1s22s22p63s23p6 4s2 3d9
] ]]]][
Stable configuration is
1s22s22p63s23p6 4s1 3d10
[ ]]]]]
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Quantum Numbers &
Atomic Orbitals
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Quantum Number Set
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EC & Quantum Numbers
n =2
N: 1s22s22p3
fff
l= 1
n =1
l= 0
ml=+1
s=+1/2
fg
ml=0
s =-1/2
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