# Electron configurations and Orbital Diagrams

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```					Electron configurations
and
Orbital Diagrams
What is an electron configuration?
It shows how the electrons are placed around an
atom.
What are they used for?
To show how an atom will bond and/or to
explain the charge an atom has when it
becomes an ion.
Number of
Energy level           electrons in
that sublevel
3

1
2       3s2
Sublevel
Letter of # of orbital   Max # e-
s           1         2
p           3         6
d           5         10
f           7         14
Order of filling
Notice the number of columns in
each section is equal to max
1s                    number of e- that each sublevel can
hold
2s   2p
s
3s   3p                                              p
4s   3d   4p                  d

5s   4d   5p
6s   4f   5d 6p                       f
7s   5f   6d 7p
Example problems
Write the electron configuration for the following
H – 1s1
Where do we start? How
He – 1s2                      about with 1s. Then just
keep moving until you have
Li – 1s22s1                   placed the correct number
Be – 1s22s2                   of electrons.

B – 1s2 2s2 2p1
C- 1s2 2s2 2p2
Noble Gas Short-Cut
Find your element on P.T. Then move all the way
to the right and up one. That is your noble gas
what period your element is in.
Let’s do potassium
Long way - K – 1s2 2s2 2p6 3s2 3p6 4s1
Short-cut - K – [Ar] 4s1
Electrons in Ar = 18, therefore we only need
one more electron
Valence Electrons
Electrons in the outermost energy level
Used to determine the charge or number of
bonds
Both have 6 valence electrons
O – [He] 2s2 2p4
because they are both in group
8 e-    2 e-
16
Se – [Ar] 4s2 3d10 4p4
34 e-   18 e-
Val e-, bonds, and charges
Gp1 gp2 gp13 gp14 gp15 gp16 gp17 gp18
1val 2val 3val 4val 5val 6val 7val 8val
1     2 3      4    3    2    1    0
1+ 2+ 3+ 4+ 3- 2- 1- 0

Octet Rule: Atoms want 8 valence electrons
Duet rule: Atoms want 2 val e- (H,He, Li, Be, B)
Orbital Diagrams
Adds the pairing and spin of electrons to E.C.
s = 1 orbital    p=3        d=5                f=7
O = [He] 2s2 2p4          You must put the max # of
orbitals down, even if you
do not need them (___)
S         P
Hund’s Rule: The most stable
Pauli’s exclusion principle: When 2    arrangement of electrons is to
electrons are in the same orbital,     place one electron in each
they must spin in opposite             orbital (spinning in the same
directions                             direction) before pairing.
More examples
V –      [Ar] 4s2 3d3       2 val e-
23 e-   18 e-

Sb – [Kr] 5s2 4d10 5p3
51 e-   36 e-

5 val e-

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