Download Electron Configurations

Quantum Number and
Electron Configurations
The arrangement of electrons in
an atom
Quantum Numbers
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Scientists use quantum number to
describe the probable region for finding
an electron
There are 4 quantum numbers.
The Principle Quantum
Number
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Symbolized by n
Indicates the main energy level occupied
the electron (the ring away from the
nucleus)
Values of n are positive integers (1,2,3,4)
As n increases, so does the distance from
the nucleus as well as the electron’s
energy.
Angular Momentum Quantum
Number
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Represented by l
Represents the shape or type of orbital that
corresponds to a particular suborbital
Each of these numbers is given a letter. We
will only deal with the first four letters.
s, p, d, f
Magnetic Quantum Number
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Represented by m
Indicates the number and orientations
of orbitals around the nucleus
This will tell us how many boxes to
make for each type of orbital when
completing orbital diagrams
The shapes that result are on Page 96
Spin Quantum Number
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Symbolized by +1/2 and -1/2 or and
Indicates the orientation of the
electrons’ magnetic field
Also known as spin
How many electrons can each
level hold?

The formula used to calculate the number
of electrons each level can hold is 2n2
Level #
1
2
3
4
5
6
7
Theoretical
2
8
18
32
50
72
98
Practical
2
8
18
32
32
18
8
So, those are the Quantum
Numbers
But what do they mean?
The answer is in something called
electron configurations
Aufbau Principle
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How did you decide where to send the
people at the Hotel Californium?
“Each electron occupies the lowest
energy orbital available”

Lowest Energy
s
1
p
3
Highest Energy
d
5
f
7
Orbital Filling Sequence and Energy
Levels
From Glencoe – Chemistry: Matter and Change
Pauli Exclusion Principle
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“One person to a bed”
“A maximum of two electrons may
occupy a single orbital sublevel, but
only if the electrons have opposite
spins”
Hund’s Rule
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The Family Situation
“Single electrons with the same spin
must occupy each equal-energy orbital
before additional electrons with
opposite spins can occupy the same
orbital.”
What does that mean in
English?
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
Much like the family at Hotel
Californium, electrons will space each
other out as much as possible before
occupying spaces close to other
electrons.
Here’s another way to think about it:
How do strangers sit on a bus as it fills
up?
In other words…
SPREAD THEM
OUT!!!
With all this talk about
electrons, here is a review
question?
Where can we find out how
many electrons an atom has?
Now we know the rules and
the number of electrons, what
do we do with them?
Remember this from earlier?
Example: Nitrogen
Electrons?
7
Electron configuration:
1s2 2s2 2p3
Lowest Energy to Highest Energy
From Glencoe – Chemistry: Matter and Change
So, if you had the orbital filling
sequence, can you fill in the
electrons?

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d,
5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p
Now, let’s take a look at Cl.
Cl has 17 electrons.
1s
2s
2p
3s
3p
Writing it without the boxes: 1s2 2s2 2p6 3s2 3p5
Orbital
diagram
Electron
Configuration
How can I remember all of
those numbers and letters?
s
p
d
f
X
1
2
3
4
5
6
7
The Diagonal Rule
X
2
3
4
5
6
7
X
X
X
3
4
5
6
7
1s 2s 2p 3s 3p 4s 3d 4p 5s
4d 5p 6s 4f 5d 6p 7s 5f 6d 7p
X
X
4 X
5 5
6 6 6
7 7 7 7