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Quantum Numbers
Electron Configuration
MI standards C4.8e, C4.8h, C4.8i, C4.9x
The Bohr Model of the Atom
I pictured
electrons orbiting
the nucleus much
like planets
orbiting the sun.
Neils Bohr
But I was
wrong! They’re
more like bees
around a hive.
WRONG!!!
The Wave-like Electron
The electron propagates
through space as an energy
wave. To understand the
atom, one must understand
the behavior of
electromagnetic waves.
Louis deBroglie
Wave Mechanical Model
Quantum Numbers
Each electron in an atom has a unique set of 4
quantum numbers which describe it.
 Principal quantum number (n)
Main energy levels, or shells
 Angular momentum quantum number (l)
Subshell, sublevel
Describes the shape of the orbital
s, p, d, or f
Magnetic quantum number (ml)
Orbital (Position)
 Spin quantum number
Principal Quantum Number
Generally symbolized by n, it denotes the shell
(energy level) in which the electron is located.
Number of electrons
that can fit in a shell:
2n 2
Angular Momentum Quantum
Number
The angular momentum quantum number, generally
symbolized by l, denotes the subshell in which the
electron is located.
Magnetic Quantum Number
The magnetic quantum number, generally
symbolized by ml, denotes the orientation of the
electron’s orbital with respect to the three axes in
space.
Spin Quantum Number
Spin quantum number denotes the behavior
(direction of spin) of an electron within a magnetic
field.
Possibilities for electron spin:
+½ or –½
Main
energy
level (n)
Subshells in Number of
main energy orbitals per
level
subshell
(n
subshells)
1
s
1
2
s
p
1
3
3
s
p
d
1
3
5
s
p
d
f
1
3
5
7
4
Number of Number
orbitals per of e- per
main
subshell
energy
level (n2)
Total
number of
e- per main
energy level
(2 n2)
1
2
2
4
2
6
8
9
2
6
10
18
16
2
6
10
14
32
Pauli Exclusion Principle
No two electrons in an atom
can have the same four
quantum numbers.
Wolfgang
Pauli
Aufbau Principle
 Electrons fill the lowest
energy level first
Hund’s Rule
 Orbitals of equal energy are
all occupied by one
electron before any orbital
is occupied by a second
electron and all singly
occupied orbitals have the
same spin
 Fill in one at a time
 “Bus rule”
Heisenberg Uncertainty Principle
“One cannot simultaneously
determine both the position
and momentum of an electron.”
You can find out where the
electron is, but not where it
is going.
Werner
Heisenberg
OR…
You can find out where the
electron is going, but not
where it is!
Schrodinger Wave Equation

d
h

V 
8  m dx
2
2
2
2
 E
Equation for probability of a
single electron being found
along a single axis (x-axis)
Erwin Schrodinger
Orbital filling table
Electron configuration of the
elements of the first three series
Irregular configurations of Cr and Cu
Chromium steals a 4s electron to half
fill its 3d sublevel
Copper steals a 4s electron to FILL
its 3d sublevel
Things get a bit more
complicated with the five d
orbitals that are found in
the d sublevels beginning
with n = 3. To remember
the shapes, think of “double
dumbbells”
…and a “dumbbell
with a donut”!
d orbital shapes
Shape of f orbitals