DATE ___________________
NOTES-030
CHEM 110 (BEAMER)
xNOTES-30:x Valence Electrons-01
DETERMINING VALENCE ELECTRONS
I.
Valence Electrons


II.
Valence Electrons
The number of
Determining the

(Please take out your periodic tables, you will need them for the remainder of the class period.)
This method is
are the
electrons
located on the
valence electrons is responsible for
number of valence electrons
pure memorization
from
outermost
chemical reactions
of an atom.
.
The Periodic Table
. When you get your periodic table for
tests and quizzes
do the following:
Practice 1)
How many valence electrons does beryllium have?
2
Practice 2)
How many valence electrons does aluminum have?
3
Practice 3)
How many valence electrons does nitrogen have?
8
Practice 4)
How many valence electrons does chlorine have?
7
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DATE ___________________
III.
Determining the

This is the
NOTES-030
number of valence electrons
A.
B.
electron configuration
to determine the number
of
best way
Periodic Table
from
method
fails
CHEM 110 (BEAMER)
.
valence electrons.
, because the
with transition elements.
Steps
1.
Write the full electron configuration.
2.
Find the highest orbital number (the first number).
3.
Circle every orbital with the number ID’d in Step 2.
4.
Count the valence electrons, and add ‘em up.
5.
Draw the Lewis Structure.
Example: Determine the number of valence electrons of sulfur using its electron configuration.
1.
Write the full electron configuration.
S:
1s2 2s2 2p6
3s2
3p4
2.
Find the highest orbital number (the first number).
S:
1s2 2s2 2p6
3s2
3p4
3.
Circle every orbital with the number ID’d in Step 2.
S:
1s2 2s2 2p6
3s2
3p4 
4.
Count the valence electrons, and add ‘em up.
2
+
4
=
6
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DATE ___________________
C.
D.
NOTES-030
CHEM 110 (BEAMER)
Example: Determine the number of valence electrons of strontium using its electron configuration.
1.
Write the full electron configuration.
Sr: 1s2 2s2 2p6
3s2
3p6 4s2 3d10 4p6 5s2
2.
Find the highest orbital number (the first number).
Sr: 1s2 2s2 2p6
3s2
3p6 4s2 3d10 4p6 5s2
3.
Circle every orbital with the number ID’d in Step 2.
Sr: 1s2 2s2 2p6
3s2
3p6 4s2 3d10 4p6 5s2
4.
Count the valence electrons, and add ‘em up.
2

2
Example: Determine the number of valence electrons of manganese using its electron configuration.
1.
Write the full electron configuration.
Mn: 1s2 2s2 2p6
3s2
3p6 4s2
3d5
2.
Find the highest orbital number (the first number).
Mn: 1s2 2s2 2p6
3s2
3p6 4s2
3d5
3.
Circle every orbital with the number ID’d in Step 2.
Mn: 1s2 2s2 2p6
3s2
3p6 4s2
3d5
4.
Count the valence electrons, and add ‘em up.
2

2
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DATE ___________________
E.
F.
NOTES-030
CHEM 110 (BEAMER)
Example: Determine the number of valence electrons of antimony (Sb) using its electron configuration.
1.
Write the full electron configuration.
Sb:
1s2 2s2 2p6
3s2
3p6 4s2 3d10 4p6 5s2 4p10 5p3
2.
Find the highest orbital number (the first number).
Sb:
1s2 2s2 2p6
3s2
3p6 4s2 3d10 4p6 5s2 4p10 5p3
3.
Circle every orbital with the number ID’d in Step 2.
Sb: 1s2 2s2 2p6
3s2
3p6 4s2 3d10 4p6 5s2 4p10
4.
Count the valence electrons, and add ‘em up.
2
+
5p3
3

5
At your desks: Determine the number of valence electrons from the electron configuration. Show your work.
Practice-1)
sodium
Practice-2)
bromine
Practice-3)
iridium (Ir)
Answer Key
Practice-1)
Na:
1s2 2s2 2p6
3s1
1
Practice-2)
Br:
1s2 2s2 2p6
3s2

1 valence electron
3p6 4s2 3d10 4p5
2
Practice-3)
Ir:
1s2 2s2 2p6
3s2
+
5

7 valence electrons
3p6 4s2 3d10 4p6 5s2 4p10 5p3 6s2 4f14 5d7
2

2 valence electrons
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