1. Bonding theories

2. Types of chemical bonds
Bond: Force that holds groups of two or more atoms together and makes the atoms function as a unit.
Example: H-O-H
Bond Energy: Energy required to break a bond.
Ionic Bond: Attractions between oppositely charged ions.
Example: Na+ Cl-

3. Types of chemical bonds
Ionic Compound: A compound resulting from a positive ion (usually a metal) combining with a negative ion (usually a non-metal).
Example: M X-  MX

4. Types of chemical bonds
Covalent Bond: Electrons are shared by nuclei. Example: H-H

5. Types of chemical bonds
Polar Covalent Bond: Unequal sharing of electrons by nuclei.
Example: H-F
Hydrogen fluoride is an example of a molecule that has bond polarity.

6. Lewis structures
Lewis Structure: Representation of a molecule that shows how the valence electrons are arranged among the atoms in the molecule.
Bonding involves the valence electrons of atoms.
Example: water:

7. Lewis structures of elements
Dots around elemental symbol
Symbolize valence electrons
Thus, one must know valence electron configuration

8. Valence electrons
In the table in your notes, write the number of valence electrons in each group.

9. Lewis dot structure
The electron dot notation that we use in chemistry is called the Lewis dot structure (after American chemist G. N. Lewis). When you draw the Lewis dot structure for an atom, start by placing a single dot at the top of the element symbol. Then proceed clockwise around the element until you have a single dot on all four sides (top, right, bottom, left). If you have more valence electrons to write, you should go clockwise around the atom again, placing a second dot right next to the first dot.

10. Lewis dot Structure
Draw the Lewis dot structures for the elements listed in your notes, following the rules on the previous slide.

11. Lithium and beryllium are metals. Do they form covalent bonds?
NO!

12. Valence Electrons and Bond Number
For each element, you can find out how many bonds they form by subtracting the number of VALENCE ELECTRONS from the number 8.
Fill out the table in your notes using this information.

13. OCTET RULE
We define the OCTET RULE as follows: Atoms tend to gain, lose, or share electrons in order to achieve a full NOBLE GAS configuration containing 8 valence electrons

14. Lewis Structures of molecules
Single Bond: Two atoms sharing one electron pair.
Example: H2

15. Lewis Structures of molecules
Double Bond: Two atoms sharing two pairs of electrons.
Example: O2

16. Lewis Structures of molecules
Triple Bond: Two atoms sharing three pairs of electrons.
Example: N2

17. Lewis Structures of molecules
Resonance Structures: More than one Lewis Structure can be drawn for a molecule.
Example: O3

18. DRAWING
LEWIS DOT
STRUCTURES
(covalent bonding)

19. Steps for Drawing the Lewis dot structure for a molecule:
Calculate the total number of valence electrons in the molecule.

20. Steps for Drawing the Lewis dot structure for a molecule:
Draw a skeleton structure for the molecule. Put the atom that normally forms the most bonds in the center.

21. Steps for Drawing the Lewis dot structure for a molecule:
Draw a line to connect each atom with a single bond. Each single bond represents 2 electrons.

22. Steps for Drawing the Lewis dot structure for a molecule:
Subtract the number of electrons you have used so far. If you have any electrons left over, place them in PAIRS around any atoms that need them.

23. Molecules
consisting of only
single bonds

24. H2O
8 e- total
Calculate the total number of
valence electrons for all the atoms.
H = 1
x 2 = 2
O = 6
x 1 = 6 8

25. H2O 8 e- total O H H Draw a skeleton structure for your molecule.
Put the atom that normally forms the most bonds in the center. O H H

26. H2O
8 e- total
Draw a line to connect each atom to the central atom with a single bond. Each single bond represents 2 electrons. O H H

27. H2O 8 e- total - 4 e- 4 e- O H H Subtract the number of
electrons that you
have used so far. O H H

28. H2O
8 e- total
- 4 e-
4 e-
If you have any electrons left over, place them IN PAIRS around any atoms that need them. O H H

29. NH3
8 e- total
Calculate the total number of
valence electrons for all the atoms.
N = 5
x 1 = 5
H = 1
x 3 = 3 8

30. NH3 8 e- total H N H H Draw a skeleton structure for your molecule.
Put the atom that normally forms the most bonds
in the center. H N H H

31. NH3 8 e- total H N H H Draw a line to connect each atom to the central
atom with a single bond. Each single bond
represents 2 electrons. H N H H

32. NH3 8 e- total - 6 e- 2 e- H N H H Subtract the number of
electrons that you
have used so far. H N H H

33. NH3
8 e- total
- 6 e-
2 e-
If you have any electrons left over,
place them IN PAIRS around any
atoms that need them. H N H H

34. CH4O
14 e- total
Calculate the total number of
valence electrons for all the atoms.
C = 4
x 1 = 4
H = 1
x 4 = 4
O = 6
x 1 = 6

35. CH4O
14 e- total
Draw a skeleton structure for your molecule.
Put the atom that normally forms the most bonds
in the center. H H C O H H

36. CH4O
14 e- total
Draw a line to connect each atom to the central
atom with a single bond. Each single bond
represents 2 electrons. H H C O H H

37. CH4O 14 e- total - 10 e- 4 e- H H C O H H Subtract the number of
electrons that you
have used so far. H H C O H H

38. CH4O 14 e- total - 10 e- 4 e- H H C O H H
If you have any electrons left over,
place them IN PAIRS around any
atoms that need them. H H C O H H

39. We will do the rest in class

40. Molecules
that contain a
double or a
triple bond

41. O2 12 e- total O = 6 x 2 = 12 Calculate the total number of
valence electrons for all the atoms.
O = 6
x 2 = 12

42. O2 12 e- total O O Draw a line to connect the atoms
with a single bond. Each single bond
represents 2 electrons. O O

43. O2
12 e- total
- 2 e-
10 e-
Subtract the number of electrons that you
have used so far. O O

44. O2 12 e- total - 2 e- 10 e- O O If you have any electrons left over,
place them IN PAIRS around any
atoms that need them. O O

45. O2
12 e- total
- 2 e-
10 e-
If there are still atoms that do not have an octet,
you can move electron pairs to form double bonds
or triple bonds to satisfy the octet rule.
MOVE THIS PAIR OF
ELECTRONS INTO
THE CENTER AREA
BETWEEN THE ATOMS
TO FORM A DOUBLE
BOND. O O

46. O2
12 e- total
- 2 e-
10 e-
Now each oxygen atom has access to an octet. O O

47. O2
12 e- total
- 2 e-
10 e-
Note that it doesn’t really matter which side
you decide to place the lone pairs. O O O O O O

48. N2 10 e- total N = 5 x 2 = 10 Calculate the total number of
valence electrons for all the atoms.
N = 5
x 2 = 10

49. N2 10 e- total N N Draw a line to connect the atoms
with a single bond. Each single bond
represents 2 electrons. N N

50. N2 10 e- total - 2 e- 8 e- N N Subtract the number of
electrons that you
have used so far. N N

51. N2 10 e- total - 2 e- 8 e- N N If you have any electrons left over,
place them IN PAIRS around any
atoms that need them. N N

52. N2
10 e- total
- 2 e-
8 e-
If there are still atoms that do not have an octet,
you can move electron pairs to form double bonds
or triple bonds to satisfy the octet rule.
MOVE THIS PAIR OF
ELECTRONS INTO
THE CENTER AREA
BETWEEN THE ATOMS
TO FORM A DOUBLE
BOND. N N

53. N2
10 e- total
- 2 e-
8 e-
If there are still atoms that do not have an octet,
you can move electron pairs to form double bonds
or triple bonds to satisfy the octet rule.
MOVE THIS PAIR OF
ELECTRONS INTO
THE CENTER AREA
BETWEEN THE ATOMS
TO FORM A TRIPLE
BOND. N N

54. N2
10 e- total
- 2 e-
8 e-
Now each nitrogen atom has access to an octet. N N

55. N2
10 e- total
- 2 e-
8 e-
Again, it doesn’t really matter which side
you decide to place the lone pairs. N N N N N N

56. We will do the rest of these practice problems in class

57. exceptions
to the octet rule:

58. BCl3
24 e- total
Calculate the total number of
valence electrons for all the atoms.
B = 3
x 1 = 3
Cl = 7
x 3 = 21

59. BCl3
24 e- total
Draw a skeleton structure for your molecule.
Put the atom that normally forms the most bonds
in the center. Cl B Cl Cl

60. BCl3
24 e- total
Draw a line to connect each atom to the central
atom with a single bond. Each single bond
represents 2 electrons. Cl B Cl Cl

61. BCl3 24 e- total - 6 e- 18 e- Cl B Cl Cl Subtract the number of
electrons that you
have used so far. Cl B Cl Cl

62. BCl3 24 e- total - 6 e- 18 e- Cl B Cl Cl
If you have any electrons left over,
place them IN PAIRS around any
atoms that need them.
You DON’T
need to do
anything to
this structure.
Boron will
be an exception
to the octet
rule, with only
six electrons
around it. Cl B Cl Cl

63. We will complete the Lewis structures for the two further exceptions to the octet rule in class

64. Polyatomic Ions

65. Polyatomic ions
When you are calculating the total number of valence electrons in a polyatomic ion, you should:
SUBTRACT electrons for cations
ADD electrons for anions

66. NH4+
8 e- total
Calculate the total number of
valence electrons for all the atoms.
N = 5
x 1 = 5
H = 1
x 4 = 4
The positive 1 charge means that you need to
SUBTRACT one electron!

67. NH4+ 8 e- total H H N H H Draw a skeleton structure for your molecule.
Put the atom that normally forms the most bonds
in the center. H H N H H

68. NH4+
8 e- total
Draw a line to connect each atom to the central
atom with a single bond. Each single bond
represents 2 electrons. + H
A polyatomic ion will
normally have brackets around it
and the charge is indicated in the top right corner. H N H H

69. OH– 8 e- total O = 6 H = 1 Calculate the total number of
valence electrons for all the atoms.
O = 6
H = 1
The negative 1 charge means that you need to
ADD one electron!

70. OH– 8 e- total – O H Draw a line to connect each atom to the central
atom with a single bond. Each single bond
represents 2 electrons.
If you have any electrons left over,
place them IN PAIRS around any
atoms that need them. – O H

71. NO3–
24 e- total
Calculate the total number of
valence electrons for all the atoms.
N = 5
x 1 = 5
O = 6
x 3 = 18
The negative 1 charge means that you need to
ADD one electron!

72. NO3– 24 e- total O N O O Draw a skeleton structure for your molecule.
Put the atom that normally forms the most bonds
in the center. O N O O

73. NO3–
24 e- total
Draw a line to connect each atom to the central
atom with a single bond. Each single bond
represents 2 electrons. O N O O

74. NO3– 24 e- total - 6 e- 18 e- O N O O Subtract the number of
electrons that you
have used so far. O N O O

75. NO3–
24 e- total
- 6 e-
18 e-
If you have any electrons left over,
place them IN PAIRS around any
atoms that need them.
MOVE THIS PAIR OF
ELECTRONS INTO
THE CENTER AREA
BETWEEN THE
ATOMS TO FORM
A DOUBLE BOND. O N O O

76. NO3– 24 e- total - 6 e- 18 e- O N O O –
If you have any electrons left over,
place them IN PAIRS around any
atoms that need them. – O N O O

77. O N O O N O O O O N O O – – – These three Lewis structures represent
RESONANCE STRUCTURES of each other. – – O N O O N O O O – O N O O

78. We will finish the practice in class