The document discusses Lewis structures and how they are used to represent the arrangement of electrons and bonds in chemical substances. It explains Lewis' theory of bonding, where atoms form bonds to achieve stable octets of electrons through ionic or covalent bonding. Lewis structures use dots or lines to show valence electrons and how they are shared between atoms. Examples show how to draw Lewis structures for molecules like H2O, SO2, and PO43- by accounting for all valence electrons. Exceptions to the octet rule are mentioned. Coordinate covalent bonding is also introduced.

1. LEWIS STRUCTURES

2. LEWIS THEORY OF BONDING
-Atoms & ions are stable if they have a noble-gas like electron
structure (stable octet)
-Electrons are most stable when paired
-Atoms form chemical bonds to achieve a stable octet of
electrons
-A stable octet may be achieved by:
-An exchange of electrons between metal and non-metal atoms
(ionic bonding)
-A sharing of electrons between 2 non-metal atoms (covalent
bonding)

3. LEWIS STRUCTURES
A Lewis structure communicates the arrangement of electrons
and bonds in a chemical substance

4. LEWIS STRUCTURES
Element Mg N S
Valence
Lewis Symbol
Energy-Level
Diagram
Electron
Configuration
Lewis Dot Diagrams correspond to Hund’s rule governing the placement
of electrons into orbitals
2+ 3- 2-
Mg
.
. N
..
.
.
. S :
.
.
..
Mg
3s
2p
2s
1s
N
2p
2s
1s
3p
3s
2p
2s
1s
S
Mg: 1s2
2s2
2p6
3s2
N: 1s2
2s2
2p3
S: 1s2
2s2
2p6
3s2
3p4

5. Draw: H2O
OH H
DRAWING LEWIS STRUCTURES

6. Draw: H2O
OH H
1 + 6 + 1 = 8 electrons
DRAWING LEWIS STRUCTURES

7. Draw: H2O
OH H
1+6+1=8 electrons
4 electrons remaining
DRAWING LEWIS STRUCTURES

8. Draw: H2O
OH H
4 electrons remaining
The octets on hydrogen
are already full.
DRAWING LEWIS STRUCTURES

9. Draw: H2O
OH H
4 electrons remaining
0 electrons
DRAWING LEWIS STRUCTURES

10. Draw: H2O
OH H
0 electrons remaining
Oxygen has a full octet, so
there is no need to form double
or triple bonds in this case
DRAWING LEWIS STRUCTURES

11. Draw: SO2
SO O
DRAWING LEWIS STRUCTURES

12. Draw: SO2
SO O
6 + 6 + 6 = 18 electrons
DRAWING LEWIS STRUCTURES

13. Draw: SO2
SO O
6+6+6=18 electrons
14 electrons remaining
DRAWING LEWIS STRUCTURES

14. Draw: SO2
SO O
14 electrons remaining
2 electrons
DRAWING LEWIS STRUCTURES

15. Draw: SO2
SO O
2 electrons
0 electrons
DRAWING LEWIS STRUCTURES

16. Draw: SO2
SO O
0 electrons
Now all atoms have a full octet
DRAWING LEWIS STRUCTURES

17. Draw: SO2
SO O
The double
bond can be on
either side
SO O
These are called resonance
structures.
SO2 has 2 resonance structures
DRAWING LEWIS STRUCTURES

18. Draw: PO4
3-
P
O
O
O
O
DRAWING LEWIS STRUCTURES

19. Draw: PO4
3-
P
O
O
O
O
6
6
6
6
5
6+6+6+6+5=29 +3 = 32 electrons
DRAWING LEWIS STRUCTURES

20. Draw: PO4
3-
P
O
O
O
O
6+6+6+6+5+3=32 electrons
24 electrons
DRAWING LEWIS STRUCTURES

21. Draw: PO4
3-
P
O
O
O
O
24 electrons remaining
0 electrons
DRAWING LEWIS STRUCTURES

22. Draw: PO4
3-
P
O
O
O
O
0 electrons remaining
There are no electrons left to
place
DRAWING LEWIS STRUCTURES

23. Draw: PO4
3-
P
O
O
O
O
Now all atoms have a full octet
DRAWING LEWIS STRUCTURES

24. Draw: PO4
3-
P
O
O
O
O
Just one more thing…
[ions must be drawn with square
brackets indicating the charge]
3-
DRAWING LEWIS STRUCTURES

25. EXCEPTIONS TO THE OCTET RULE
Sometimes, central atoms do not obey the octet rule
Under-filled octets:
Be – 2 bonds (4 electrons)
B – 3 bonds (6 electrons)
Over-filled octets:
P – 5 bonds (10 electrons)
S – 6 bonds (12 electrons)

26. COORDINATE COVALENT BONDING
Sometimes, when a covalent bond forms between 2 atoms, both
shared electrons are donated by 1 atom
Example: NH4
+
Example: Al2Cl6

27. LEWIS STRUCTURES
Homework:
Read pages 194 & 195 (if have not already)
Page 200 #1, 2
Page 204 #1, 2
Page 205 #4, 5