1. Unit 7
Covalent Bonding

2. Bonding A metal & a nonmetal transfer electrons An ionic bond
Two metals mix
An alloy (Metallic bond)
What do two nonmetals do?
Neither one will give away an electron
So they share their valence electrons
This is a covalent bond

3. Covalent Bonding Nonmetals hold on to their valence electrons
They can’t give away electrons to bond
Still want to be stable!
Need noble gas configuration (octet rule)
Get it by sharing valence electrons with each other.
By sharing, both atoms get to count the electrons toward noble gas configuration.

4. F F Covalent Bonding Fluorine has seven valence electrons
A second atom also has seven
By sharing electrons…
Both end with full orbitals F F

5. F F Covalent bonding Fluorine has seven valence electrons
A second atom also has seven
By sharing electrons…
Both end with full orbitals F F
8 Valence electrons

6. F F Covalent bonding Fluorine has seven valence electrons
A second atom also has seven
By sharing electrons
Both end with full orbitals F F
8 Valence electrons

7. Ways to Illustrate Covalent Bonds
Molecular formula: shows the number of atoms of each element in a molecule.
Ex. PF3
Lewis Structures: uses dots to represent bonding between molecular compounds
Structural Formulas: shows the arrangement of atoms and bonds
Shared electron dots are replaced with a dash
Models: ball and stick (3-D versions)

8. Single Covalent Bond Occurs between nonmetals or a nonmetal & hydrogen
Sharing of two valence electrons (1 pair)
Different from an ionic bond – electrons are SHARED not transferred

9. An example with dots… It’s like a jigsaw puzzle
You will be given the formula
You put the pieces together to make everyone stable or happy 
Most atoms need an octet
H & He need a duo
Carbon is often the center

10. H O Water Each hydrogen has 1 valence electron and wants 1 more
The oxygen has 6 valence electrons
and wants 2 more
They share to make each other “happy” H O

11. H O Water Put the pieces together The first hydrogen is happy
The oxygen still wants one more H O

12. H O H Water The second hydrogen attaches
Every atom has full energy levels H O H

13. Structural formula…
Replace shared dots with a dash H O H

14. Practice – Dots & Structures
CH3I
H2S
CH2Cl2
NH3
C2H6
SCl2
AsF3
SiH4
CHF3

15. Multiple Bonds
Sometimes atoms share more than one pair of valence electrons.
A double bond is when atoms share two pair (4) of electrons.
A triple bond is when atoms share three pair (6) of electrons.

16. C O Carbon dioxide CO2 - Carbon is central atom
Carbon has 4 valence electrons
Wants 4 more
Oxygen has 6 valence electrons
Wants 2 more C O

17. Carbon dioxide
Attaching 1 oxygen leaves the oxygen 1 short and the carbon 3 short C O

18. Carbon dioxide
Attaching the second oxygen leaves both oxygen 1 short and the carbon 2 short O C O

19. Carbon dioxide
The only solution is to share more O C O

20. Carbon dioxide
The only solution is to share more O C O

21. Carbon dioxide
The only solution is to share more O C O

22. Carbon dioxide
The only solution is to share more O C O

23. Carbon dioxide
The only solution is to share more O C O

24. Carbon dioxide
The only solution is to share more O C O

25. O C O Carbon dioxide The only solution is to share more
CO2 requires two double bonds
Each atom gets to count all the atoms in the bond O C O

26. O C O Carbon dioxide The only solution is to share more
CO2 requires two double bonds
Each atom gets to count all the atoms in the bond
8 valence electrons O C O

27. O C O Carbon dioxide The only solution is to share more
CO2 requires two double bonds
Each atom gets to count all the atoms in the bond
8 valence electrons O C O

28. O C O Carbon dioxide The only solution is to share more
CO2 requires two double bonds
Each atom gets to count all the atoms in the bond
8 valence electrons O C O

29. Carbon Dioxide
Replace the shared pairs with dashes O C O

30. Practice O2
CS2
CH2O
N2F2
NO2
HCN (triple)
C2H2 (triple)

31. Exceptions to the Octet Rule/Patterns of Bonding
1. Some elements with odd number of valence electrons
BF3
PCl5
2. Coordinate covalent bonding

32. Coordinate Covalent Bond
When one atom donates both electrons in a covalent bond
Carbon monoxide (CO) O C

33. Coordinate Covalent Bond
When one atom donates both electrons in a covalent bond.
Carbon monoxide (CO) C O

34. Coordinate Covalent Bond
When one atom donates both electrons in a covalent bond.
Carbon monoxide (CO) C O O C

35. Summary of Covalent Bonding
Covalent bonds occur by SHARING electrons
Occurs between NONMETALS
End product is called a MOLECULE
1. Molecular compound - formed with different elements
2. Diatomic molecules - 2 of the same atom
There are 7 elements that always form diatomic molecules
H2 , N2 , O2 , F2 , Cl2 , Br2 , and I2

36. Diatomic Molecules

37. Naming Molecular Compounds
Easier than ionic compounds
No balancing charges
1 mono-
2 di-
3 tri-
4 tetra-
5 penta-
6 hexa –
7 hepta –
8 octa –
9 nona –
10 deca –

38. Naming Molecular Compounds
1st element – add the prefix that matches the subscript
Exception – do not add “mono-” if there is 1 atom
No aa, oo, or ao double vowels
2nd element – add the prefix that matches the subscript
Still ends in -ide

39. Naming CO2 1st element = Carbon; subscript 1 Remember exception
2nd element = oxygen; subscript 2
Prefix for 2 is di-
“Dioxide”
Full name = carbon dioxide

40. Practice Naming S2Cl2 Disulfur dichloride CS2 Carbon disulfide SO3
Sulfur trioxide
P4O10
Tetraphosphorus decoxide

41. Name  Formula Just look at the prefixes! Carbon tetrachloride
1 Carbon, 4 Chlorine atoms
CCl4
Iodine heptaflouride
Dinitrogen monoxide
Sulfur dioxide

42. Common Names NH3 – Nitrogen trihydride Ammonia
H2O – dihydrogen monoxide
Water 
NH3 – Nitrogen trihydride
Ammonia
CH4 – carbon tetrahydride
Methane
HCl – Hydrogen monochloride
Hydrochloric acid

43. Names to know! NH3 - Ammonia H2O - Water CO – Carbon monoxide
CO2 – Carbon dioxide
SO2 – Sulfur dioxide
CFl4 – Carbon Tetraflouride

44. Molecular Shapes
Lewis diagrams & structural formulas are 2-dimensional
Real molecules are 3-D
If there are 2 atoms, the molecule has a LINEAR shape (no other options!)
Carbon monoxide (CO)
If it has more than 2, how do we figure out the shape?

45. VSEPR Theory Valence Shell Electron Pair Repulsion Theory
Used to predict shape of a molecule
Negative electrons repel each other and pairs want to be as far apart as possible

46. Linear
Linear: 2 atoms around central atom, no unshared pairs on central atom
With three atoms the farthest the two outer molecules can get apart is 180º.
Will require 2 double bonds or one triple bond C O
180º

47. Trigonal Planar
Trigonal planar: 3 atoms around central atom, no unshared pair on central atom.
Angle = 120°

48. H H C H H Tetrahedral 4 molecules around a central atom
All single bonds
Must think in 3-D! H H C H H

49. Tetrahedral
Tetrahedral: 4 atoms around central atom, no unshared pair on central atom
A pyramid with a triangular base. H
109.5º C H H H

50. So far… 2 3 4 SHAPE # SHARED PAIRS FROM THE CENTRAL ATOM
# UNSHARED PAIRS ON THE CENTRAL ATOM
LINEAR 2
TRIGONAL PLANAR 3
TETRAHEDRAL 4

51. Molecular Shapes
But what if there are unshared pairs on the central atom?
They still repel each other…

52. Bent
Bent: 2 atoms around central atom, 1 or 2 unshared pair(s) on central atom. O H O H
<109.5º H H

53. Bent
Ball and stick model does not show unshared electron pairs

54. Pyramidal
Pyramidal: 3 atoms around central atom, 1 unshared pair on central atom N H N H H H
<109.5º H H

55. Pyrimidial
Ball and stick model does not show unshared electron pairs

56. Trigonal Bipyramidal
Trigonal bipyramidal: 5 atoms around central atom, no unshared pair on central atom
Angles = 90° and 120°

57. Adding to the chart… 2 1 or 2 3 1 5 SHAPE
# SHARED PAIRS FROM THE CENTRAL ATOM
# UNSHARED PAIRS ON THE CENTRAL ATOM
BENT 2
1 or 2
PYRAMIDIAL 3 1
TRIGONAL BIPYRAMIDAL 5

58. So how do I determine the shape of a given molecule?
Draw the Lewis diagram
Count the shared and unshared pairs
Use the VSEPR Theory to determine the shape

59. Which type of bond is it? Look at which elements are involved
Metal & nonmetal = ionic bond
2 nonmetals = covalent bond
Electronegativity – measure of a tendency of an atom to attract a pair of electrons
Influenced by amount of positive charge in the nucleus & electron shielding

60. Differences in Electronegativity.
Big difference between values (greater than 1.70)
One atom REALLY wants the electrons and the other…not so much
Ionic bonding  ionic compound
Smaller difference between values (less than 1.70)
Both have “equal” attraction for the e-
Covalent bonding  molecule

62. Differences in Electronegativity
Medium difference
Still a bit of a tug of war over e-
Unequal sharing of electrons
Results in a POLAR covalent bond
Positive and negative poles
Dipole – partially negative on one side, partially positive on the other

63. Polar Covalent Bond

65. Differences in Electronegativity
Very small difference
Share electrons equally
NONPOLAR covalent bond
No positive and negative poles

66. Nonpolar Covalent Bond

68. Polar vs. nonpolar molecules
Look at polarity of each bond
All nonpolar bonds = nonpolar molecule (O2)
Look at the overall shape
Symmetrical polar bonds cancel each other out so molecule = nonpolar (CO2, CCl4)
Nonsymmetrical polar bonds = polar molecule (H2O)

69. Dipole-dipole attraction
Attraction between + part of one dipole and - part of another dipole
Hydrogen bond - between an electronegative atom and a hydrogen atom bonded to another electronegative atom
Often involves F, N, or O
Strongest of the intermolecular forces

70. Hydrogen Bonding H O d+ d- H O d+ d-

71. Hydrogen Bonding

72. Van der Waals – London dispersion force
Weak intermolecular force caused by negative electrons on one side of a cloud being attracted to a nearby positive nucleus
Constantly changing

73. Properties of Molecular Compounds
Poor conductors of heat & electricity
Often found as liquids or gases
Weaker attraction between atoms
Low melting & boiling points

74. IONIC vs COVALENT

75. Carbon (Organic) Chemistry
Carbon plays a dominant role in the chemistry of living things
Bonding stability
4 valence electrons
Very unlikely to form ionic bonds
Can form covalent bonds with LOTS of different elements (especially H & O)
Small molecules link together resulting in the formation of a large variety of structures often with repeating subunits

76. Examples of carbon-based compounds
Simple hydrocarbons
Small carbon molecules with functional groups
Complex polymers
Biological molecules

77. Simple Hydrocarbons
Petrochemicals – Propane, Butane, Octane

78. Functional groups
Specific groups of atoms that are responsible for chemical characteristics of a compound
ALWAYS a close relationship between properties & structure (aspirin, vitamins, insulin)

79. Complex Polymers & Biological Molecules
Natural polymers
Proteins, nucleic acids
Synthetic polymers
Polythene , Polystyrene
Kevlar
Nylon

80. Common organic molecules
CH4
C2H6
C2H4
C2H2
CH3CH2OH
CH2O
C6H6
CH3COOH