Bono
"The less you know, the more you believe."
Chapter 13
Day 2
Quantum Numbers and
Electron Configurations
Models of the Atom
Dalton
Thomson
Rutherford
Bohr
Neils Bohr model of the Atom:
Electrons can be in 1 of many “principle
energy levels”, but cannot be in between
any of these
energy levels.
n=1
n=2
n=3
Each Principle
Energy Level (n) is
given a number
Electrons move around the nucleus like planets
move around the sun.
Unfortunately, Bohr’s model of the Hydrogen atom
turned out to be incorrect, so a new model was
introduced.
Not This!
But, This!
What are the Quantum Numbers?
– they give the approximate
location of electrons in an atom.
 They are actually represented by letters.
 N – distance (size of orbital)
 l – Shape of orbital
 m – orientation in space of orbital
 s – spin of the electron
 Remember
Erwin Schrödinger, using complex mathematics,
calculated the probability of where an electron is
located.
The probability of an electron in the first principle energy level:
An orbital is drawn that
encloses the region
where the electron is
found 90% of the time.
First Energy Level (n=1) can contain 1 sublevel orbital
Second Energy Level (n=2) can contain 2 sublevel orbitals
Third Energy Level (n=3) can contain 3 sublevel orbitals and so on…
There are many types of sublevels:
Name
Lowest
Energy
Shape
Maximum # of
electrons
s
2
Spherical
p
6
Highest
Energy
Dumbell
Dumbell
Name
Shape
Maximum #
of electrons
Lowest
Energy
d
10
f
Highest
Energy
f
14
The next sublevel is g. How many electrons would
it hold?
What type of sublevel orbital(s) would be found in the first principle
energy level (n=1)? How many electrons will it hold?
What type of sublevel orbital(s) would be found in the second principle
energy level (n=2)? How many electrons will it hold?
What type of sublevel orbital(s) would be found in the third principle
energy level (n=3)? How many electrons will it hold?
1s vs 2s vs 3s orbitals
Each sublevel orbital can hold 2 electrons, which have opposite magnetic
fields. Therefore, we say that each electron has a spin, which is opposite of
each other. This is symbolized by:
Called the
Pauli
exclusion
principle
Electron Configurations
Electron
Configurations
 Using
quantum numbers to give the
arrangement of electrons around the
nucleus.
 There are three rules that must be
followed!
Rule #1
 AUFBAU

principle
Electrons fill low energy orbitals first
• s,p,d then f
• Filling order

1s2s2p3s3p4s3d4p5s4d5p6s4f5d6p7s5f6d7p
Rule #2
 Pauli

Exclusion Principle
Since there are two possible spins for an
electron, no more than two electrons may
fill an orbital.
• Remember: s = 1 orbital, p = 3 orbitals, d = 5
orbitals and f = 7 orbitals
Rule # 3
 Hund’s

Rule
When multiple shapes are present,
electrons fill orbitals with parallel spins
before pairing up.
• Must follow rule #2!

Example 2p
Write the following
electron configurations
1.
2.
3.
4.
5.
Li
Na
Be
C
Si
Using the Periodic Table
1.
2.
Read from left to right and top to
bottom.
Stop when you:
a.
b.
c.
3.
Reach the end of a row
Change color
Reach the element of interest
Try the following Mg, B, Ne and Cl
Short-Cut
 Skip
back to the previous Noble Gas (core
electrons) and start with the element after
that.
 Try: I, U, Fe