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Friday, Nov. 2nd: “A” Day
Monday, Nov. 5th: “B” Day
Agenda
Finish Section 3.3: “Electron Configuration”
Quantum numbers, Pauli exclusion principle,
electron configuration, aufbau principle,
Hund’s rule
Electron Configuration Movie/Worksheet
Homework:
Electron Configuration Movie Worksheet
Quantum Numbers
Quantum number: a number that specifies the
properties of electrons
Each electron has 4 quantum numbers:
1. Principal quantum number, n:
 The main energy level (row on periodic table)
2. Angular momentum quantum number, l:
 The shape of the orbital (s, p, d, f)
3. Magnetic quantum number, m:
 The orientation of the orbital around the nucleus
4. Spin quantum number, +½ or -½ (↑↓)
Pauli Exclusion Principle
Remember, each orbital can hold a maximum of
2 electrons.
In 1925 the German chemist Wolfgang Pauli
established a rule is known as the Pauli exclusion
principle.
Pauli exclusion principle: the principle that states
that two particles of a certain class cannot be in
the exact same energy state.
In plain English: no two electrons in the
same atom can have the same four
quantum numbers.
Electron Configuration
Electron configuration: the arrangement of
electrons in an atom.
Like all systems in nature, electrons in atoms
tend to assume arrangements that have the
lowest possible energies.
An electron configuration of an atom shows
the lowest-energy arrangement of the
electrons for the element.
Shapes of s, p, and d Orbitals
**Each Orbital Can Hold a Maximum
of 2 Electrons**
There is only 1 s orbital for each main energy level.
The s orbital can only hold 2 electrons.
There are 3 p orbitals for each main energy level.
The p orbitals can hold 2 electrons each for a total
of 6.
There are 5 d orbitals for each main energy level.
The d orbitals can hold 2 electrons each for a total
of 10.
There are 7 f orbitals for each main energy level.
The f orbitals can hold 2 electrons each for a total of
14.
An Electron Occupies the Lowest
Energy Level Available
Aufbau principle: the principle that states that
the structure of each successive element is
obtained by adding one proton to the nucleus of
the atom and one electron to the lowest-energy
orbital that is available.
In plain English: electrons occupy orbitals that
have the lowest energy first.
Orbital Filling Chart
This diagrams shows
how the energy of the
orbitals can overlap.
Because the 4s orbital
has a lower energy than
the 3d orbital, it will fill
first.
Hund’s Rule
Electron orbitals are filled according to Hund’s
Rule.
Hund’s rule: the rule that states that for an atom
in the ground state, the number of unpaired
electrons is the maximum possible and these
unpaired electrons have the same spin.
 In plain English: all orbitals in a given energy
level must have 1 electron each before any
pairing occurs.
Don’t HOG electrons!
Writing Electron Configurations
There are 2 different ways that electron
configurations can be represented:
1. With arrows:
____ ____ ____ ____ ____
1s
2s
2p 2p
2p
 Each horizontal line represents an orbital.
 Each arrow represents an electron with a
different spin.
 Which element do you think this this?
Writing Electron Configurations
2. With electron configuration notation:
1s22s22p5
 The big numbers indicate the main energy
level, n (row on periodic table)
 The letters indicate the orbital type.
 The superscripts show the number of
electrons.
 Which element do you think this this?
Electron Configuration Practice
Use arrows to write the electron configuration for
an atom of an element whose atomic number is 8.
Atomic Number = # of protons
# protons = # electrons = 8
Use the orbital filling chart to place the 8 electrons
in their proper orbitals.
Remember, the s orbital can only hold 2 electrons
and the 3 p orbitals can hold 2 electrons each for a
total of 6.
____ ____ ____ ____ ____
1s
2s
2p 2p
2p
Sample Problem C, pg. 98
Use arrows AND electron configuration notation to
write the electron configuration for an atom whose
atomic number is 20.
Atomic Number = # of protons
# protons = # electrons = 20
Use the orbital filling chart to place the 20
electrons in their proper orbitals:
__ ____ ____ ____ ____ ____ ____ ____ ____ ____
1s
2s
2p 2p 2p 3s
3p 3p 3p 4s
1s22s2sp63s23p64s2
Electron Configuration Practice
Use arrows AND electron configuration notation to
write the electron configuration for an atom that
has 17 electrons.
Use the orbital filling chart to place the 17
electrons in their proper orbitals:
____ ____ ____ ____ ____ ____ ____ ____ ____
1s 2s
2p 2p
2p
3s
3p 3p 3p
1s22s22p63s23p5
Movie:
“Writing Electron Configurations”
Welcome back Mr. Sweatervest!
Follow along and complete the student examples
as they are being discussed in the movie.
The rest of the worksheet,
front and back, is homework.
Homework
Complete the rest of the movie worksheet.
*Next time section 3.3 work day!*