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Transcript
Use the Venn Diagram to compare and contrast
the Bohr Model of the atom with the Quantum
Mechanical Model of atom
Bohr Model
Quantum Model
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Energy level
Atomic orbital
Quantum
Atomic number
Quantum mechanical model
Mass number

If this rock were to tumble
over, it would end up at a
lower height. It would have
less energy than before, but
its position would be more
stable. You will learn that
energy and stability play an
important role in
determining how electrons
are configured in an atom.
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In nature, change generally proceeds toward
the lowest possible energy level
High energy systems are unstable and lose
energy to become more stable
Electrons are arranged with lowest possible E
level- we call this the electron configuration
SLO for 2/24/16
Students will be able to summarize the
Aufbau principle, the Pauli exclusion
principle, and Hund's rule.
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An electron configuration is the way that
electrons are arranged in various orbitals
around the nucleus
3 Rules must be followed to write an electron
configuration
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
Aufbau Principle
Pauli Exclusion Principle
Hund’s Rule
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Electrons fill the orbitals with LOWEST
ENERGY first
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So in the chart, start with the 1s orbital and work
your way upward
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An atomic orbital can hold at most 2 electrons
To occupy the same orbital, the electrons must
have opposite spins
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The opposite spins are indicated by arrows pointing
in opposite directions (one up and one down)
Spinning electrons produce magnetic fields, which
allow the electrons to attract (the attraction balances
out the repulsion of like charges)
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Hund’s rule states that electrons occupy
orbitals of the same energy in a way that makes
the number of electrons with the same spin
direction as large as possible.
In other words, electrons fill orbitals one at a
time and have parallel spins.
After all orbitals in a sublevel have one
electron, added electrons double up in orbitals
and have opposite spins to electrons already
there.
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For oxygen: 8 electrons
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For oxygen: 8 electrons
The arrows represent the spin of the electron.
Notice that the electrons are spinning opposite
ways when they are together and the same way
in the orbitals with just one electron each
There are 6 paired electrons and 2 unpaired
electrons
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
Notice that all inner electrons are paired- there
are 2 arrows in a box
Some outer electrons might not be paired- there
may be only 1 arrow in a box

Look at the periodic table to find the correct number of
electrons
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(look at the atomic number to find protons and for neutral
atoms, the number of electrons matches the number of protons)
Use the Aufbau chart to figure out where the electrons
go. Start with 1s and follow the arrows.
The numbers at the top of the chart indicate the
maximum number of electrons that can be placed in
that sublevel.
Fill up each sublevel until you have reached the correct
number of electrons, which you found earlier on the
periodic table

Calcium (Ca)

Bromine (Br)


Use the periodic table to help you check your
work.
The last electrons written in your electron
configuration should be the same as the
principle energy level, sublevel, and number of
electrons in the outermost energy level as
indicated on your periodic table!
•
Valence electrons- outer shell electrons that
determine the chemical properties of elements
•
•
•
Since they are in the outer shell, you can find out
how many are present by counting the electrons in
the highest principle energy level
This will ALWAYS include just the s and/or p
orbitals
Oxygen has 8 electrons 1s22s22p4
•
The highest principal energy level is 2. It contains 6
electrons, so there are 6 valence electrons

Shorthand electron configurations:
find the element you want on the P.T.
 look up one row and find the noble gas in that row
 Write the noble gas chemical symbol in brackets
 Look back at the periodic table and find the information
above the element you’re working with
 Fill in the values for n and n-1 by looking at the row the
element is in.
 Make sure you pay attention to the presence of possible d
and f orbitals if your element is in the p block.

 You’ll need to look at the aufbau chart for this
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Example of Shorthand notation:
Chlorine: 17 electrons
Noble gas above chlorine: Ne
Neon has 10 electrons. The last 7 (to get to 17
electrons) must be written out.
Above Cl you will see ns2…np5
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Cl is in row 3, so replace n with 3.
There are no d orbitals after 3s, so write the
answer like this:

[Ne]3s2 3p5
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According to the aufbau chart, copper should have this
electron configuration:
Cu: 1s22s22p63s23p64s23d9
Instead, it has this electron configuration:
Cu: 1s22s22p63s23p64s13d10
Exceptions occur in groups 6B and 1B because:
Sublevels are most stable when they are full
Sublevels are fairly stable when they are ½ full
Sublevels lack stability when they are partly full
The d sublevel becomes more stable in groups 6B and 1B
by stealing an electron from the previous s sublevel

Fill out your exit slip about what you
learned today:

State the names of the three rules that govern
the filling of atomic orbitals by electrons and
give a short description of what the rule
entails.


Reading Assignment: Section 5.2
Written Assignment: pg. 152, #35-39,
41-43
Pg. 152, #35-39, 41-43
35. Aufbau Principle- Electrons occupy the lowest
possible energy levels. Pauli Exclusion
Principle- An atomic orbital can hold at most
two electrons. Hund’s Rule- One electron
occupies each of a set of orbitals with equal
energies before any pairing of electrons occurs.
36. 2s, 3p, 4s, 3d
37. B and C
38. a. 2
b. 2 c. 6 d. 14 e. 6 f. 10 g. 2 h. 6
Pg. 152, #35-39, 41-43
39. The p orbitals in the third quantum level have
three electrons.
41. a. 1s22s22p63s1
b. 1s22s22p63s23p64s1
c. 1s22s22p63s23p63d104s24p64d105s25p5
d. 1s22s22p6
42. a. 2
b. 3 c. 1 d. 6
43. a. 8
b. 8 c. 8