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Quantum Numbers
What are they?
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Characterization of the orbital that an
electron occupies
Describes the following:
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distance from the nucleus
shape
position with respect to the 3 dimensional axis
direction of spin of the electron
What are orbitals?
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Area to that an electron pair can reside in
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There are four main “shapes” for orbitals
Orbitals can be found in shells which are
main energy levels
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aka the rings or orbits around a nucleus
Principal Quantum Number
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Abbreviated as n
Represents the
distance of an
electron from the
nucleus & the main
energy level of the
electron.
n is numerically
represented by
positive integers.
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n2 = # of orbitals in a
shell
2 n2 = # of electrons
in a shell
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Each orbital can house
an electron pair!
Shell #
#e-
1
2
2
8
3
18
4
32
5
50
Angular Momentum
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Abbreviated by l
Describes the shape
of an orbital by using
a number and letter
designation.
Determined by all
values between n1…0
l
Letter
0
s
1
p
2
d
3
f
Shapes
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s orbital is spherical
p orbital looks like a dumbell
d orbitals look like 2 dumbells
f orbitals look like flowers
Magnetic Quantum Number
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Abbreviated by ml
Represents the 3 dimensional orientation
of an orbital
Assumes all values –l…0…+l
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If n=1
Then l=0
So ml=0
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Think of spinning a
basketball on your
finger…does it really
change where it is in
3D??
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For a p orbital…
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n=2
l=1
ml= -1, 0, +1
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The p orbital can exist
in different planes in 3D
Spin Quantum Number
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Abbreviated by ms
Uses +1/2 or -1/2
Indicates the direction of spin of an
electron
Electrons in the same orbital have
opposite spins!
A Picture of the Spinning
Electron
How do we determine QN’s?
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Must use 3 main rules and determine the
electron configuration!
Aufbau Principle
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Electrons must enter the lowest shell and
orbital first!
Hund’s Rule
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orbitals of equal energy will be occupied
by one electron before a second one may
enter
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No one can have seconds until everyone has
gone through once!!
Pauli’s Exclusion Principle
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No 2 electrons in the same orbital can
have the same 4 Quantum Numbers!!
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Don’t worry because each will have an
opposite spin!!