Atoms And Elements Worksheet Page 14
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18Periodic table
Electron
Valence
Group
Example
group
configuration
electrons
number
2
2
6
1
Group IA
Na
1s
2s
2p
3s
1
1
2
2
6
2
Group IIA
Mg
1s
2s
2p
3s
2
2
2
2
6
2
1
Group IIIA
Al
1s
2s
2p
3s
3p
3
3
2
2
6
2
2
3s
3p
Group IVA
Si
1s
2s
2p
4
4
2
2
6
2
3
Group VA
P
1s
2s
2p
3s
3p
5
5
2
2
6
2
4
Group VIA
S
1s
2s
2p
3s
3p
6
6
2
2
6
2
5
Group VIIA
Cl
1s
2s
2p
3s
3p
7
7
2
2
6
2
6
3s
3p
Group VIIIA
Ar
1s
2s
2p
8
8
Worked Example 2-6
Give the number of valence electrons for each the following: K, Ba, O, Br, and P.
Solution
For group A elements, you can predict the number of valence electrons by noting
the group number of each element from the periodic table.
K is in group IA …... K has 1 valence electron
Ba is in group IIA ….Ba has 2 valence electrons
O is in group VIA ….O has 6 valence electrons
Br is in group VIIA…Br has 7 valence electrons
P is in group VA …... P has 5 valence electrons
Lewis Structures (Electron-dot Formulas)
To keep track of valence electrons we use a notation called electron-dot formula. In this
notation, the outer electrons are shown as dots on the sides of the symbol for the element.
Each dot corresponds to an outer-shell electron. Although dot placement isn’t critical, one
method is to begin at the top of the symbol and move clockwise around it placing dots on
each side of the symbol one at a time. You must not pair any electrons until all four sides
have one dot.
IA
IIA
IVA
IIIA
VA
VIA
VIIA
.
H
.
.
.
..
.
..
..
.
.
.
.
.
.
.
.
Li
Be
B
C
N
O
F
.
..
.
.
.
2-14
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