Electron Arrangement
Another link for review
http://www.mrcoulter.com/LECTURE
S/28Elec-config.pdf
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Quantum Numbers
• Quantum numbers specify the properties of
atomic orbitals and the properties of electrons
in orbitals. This is also known as probable
location of electrons about the nucleus of an
atom.
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Principal Quantum Number, n
Indicates the
main energy
level occupied
by an electron
(n=1,2,3,…7)
http://library.thinkquest.org/C006669/ 3
Angular momentum quantum number
has 4 basic shapes
•
•
•
•
•
The values and shapes are
l=0
s shape
l=1
p
l=2
d
l=3
f
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Angular Momentum Quantum
Number, l
• s shape
sparknotes.com
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p shape
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d shaped orbitals
Courtesy of bluelight.ru
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f orbitals
f orbitals are very complex and you will not be
responsible for drawing them. The site below
has more informtion.
http://www.d.umn.edu/~pkiprof/ChemWebV2/
AOs/ao4.html
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Spin quantum number, s, has only two
possible values
• Has only two possible values: +1/2, -1/2.
• See table 2 on page 110 to get a better idea of
the number of orbitals and electrons per
energy level.
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Electron Configurations
I. Rules Governing Electron Configurations
II. Orbital Notation
III. Electron-Configuration Nottion
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Rules Governing Electron
Configurations
I. Aufbrau Principle – an electron occupies the
lowest-energy orbital that can receive it.
This is really a thought
process in which we think
about building up an atom
from the one that preceeds it
in atomic number, by adding
a proton and neutrons to the
nucleus and one electron to
the appropriate atomic
orbital.
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Source: https://chemistry.twu.edu/tutorial/AufbauSum.html
Rules Governing Electron
Configurations, cont.
II. Pauli Exclusion Principle – no two electrons
in the same atom can have the same set of
four quantum numbers.
The box at left shows the
different spin states of two
electrons in the same
orbital. This drawing is the
electron configuration of a
helium atom’s 1 s orbital.
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Rules Governing Electron
Configurations, cont.
III. Hund’s Rule – orbitals of equal energy are
each occupied by one electron before any
orbital is occupied by a second electron, and
all electrons in singly occupied orbitals must
have the same spin state.
en.citizendium.org
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Periodic Table:
Orbitals
Source: chem.wisc.edu
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Orbital Notation
Pair of electrons in an orbital
Unpaired electron
Orbital name
What element is this showing?
Fluorine
Source: naturalphilosophers.org
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Sample problems
Write the electron configuration notation for
Silicon and Scandium (use the Aufbrau diagram)
Si has 14 electrons
2 in 1s 2 in 2s
6 in 2p 2 in 3s
2 in 3p
written as:
1s2 2s2 2p6 3s2 3p2
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Scandium Electron Configuration
Notation
Sc has 21 electrons
1s2 2s2 2p6 3s2 3p6 4s2 3d1
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Scandium Notations
Electron Configuration Notation
1s2 2s2 2p6 3s2 3p6 4s2 3d1
Orbital Notation
__ __ __ __ __ __ __ __ __ __ __ __ __ __ ___
1s 2s
2p
3s
3p
4s
3d
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Notations,cont.
Noble gas notation – back up to the last noble gas prior to the
element and add orbitals:
[Ar}4s23d1
Dot notation - shows only the outer shell electrons for an
element’s atom (maximum number of e’s in an outer shell
is 8) for Sc: 4s2 for F: 2s22p5
for Ne: 2s22p6
..
..
Sc :
:F:
: Ne :
.
..
Other info: atoms are more stable when they have a halffilled or completely filled outer shell
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