1. Covalent Bonding
Bonding models for methane, CH4. Models are NOT reality. Each has its own strengths and limitations.

2. The Octet Rule and Covalent Compounds
Covalent compounds tend to form so that each atom, by sharing electrons, has an octet of electrons in its highest occupied energy level.
Covalent compounds involve atoms of nonmetals only.
The term “molecule” is used exclusively for covalent bonding

3. The Octet Rule: The Diatomic Fluorine Molecule1s 2s 2p
Each has seven valence electrons F 1s 2s 2p F F

4. The Octet Rule: The Diatomic Oxygen Molecule1s 2s 2p
Each has six valence electrons O 1s 2s 2p O O

5. The Octet Rule: The Diatomic Nitrogen Molecule1s 2s 2p
Each has five valence electrons N 1s 2s 2p N N

6. Lewis Structures
Lewis structures show how valence electrons are arranged among atoms in a molecule.
Lewis structures Reflect the central idea that stability of a compound relates to noble gas electron configuration.
Shared electrons pairs are covalent bonds and can be represented by two dots (:) or by a single line ( - )

7. The HONC Rule Hydrogen (and Halogens) form one covalent bond
Oxygen (and sulfur) form two covalent bonds
One double bond, or two single bonds
Nitrogen (and phosphorus) form three covalent bonds
One triple bond, or three single bonds, or one double bond and a single bond
Carbon (and silicon) form four covalent bonds.
Two double bonds, or four single bonds, or a triple and a single, or a double and two singles

8. Completing a Lewis Structure -CH3Cl
Make carbon the central atom (it wants the most bonds, 4)
Add up available valence electrons:
C = 4, H = (3)(1), Cl = 7 Total = 14
Join peripheral atoms
to the central atom with electron pairs. H .. .. .. .. .. H C Cl .. ..
Complete octets on
atoms other than hydrogen with remaining electrons H

9. Bond Length and Bond Energy
Length (pm)
Energy (kJ/mol)
C - C
154
346
C=C
134
612
CC
120
835
C - N
147
305
C=N
132
615
CN
116
887
C - O
143
358
C=O
799
CO
113
1072
N - N
145
180
N=N
125
418
NN
110
942

10. Resonance
Occurs when more than one valid Lewis structure can be written for a particular molecule.
These are resonance structures.
The actual structure is an average of
the resonance structures.

11. Resonance in Benzene, C6H6

12. Naming Binary Molecular Compounds

13. Binary Molecular Compounds
Compounds between two nonmetals
First element in the formula is named first.
Keeps its element name
Gets a prefix if there is a subscript on it
Second element is named second
Use the root of the element name plus the -ide suffix
Always use a prefix on the second element

14. List of Prefixes 1 = mon(o) 2 = di 3 = tri 4 = tetra 5 = penta
6 = hexa
7 = hepta
8 = octa
9 = nona
10 = deka
List of Prefixes

15. Naming Binary Compounds
diphosphorus pentoxide
CO2 =
carbon dioxide
CO =
carbon monoxide
N2O =
dinitrogen monoxide

16. Practice – Write the Formula
Compound Name
Compound Formula
Carbon dioxide
Carbon monoxide
Diphosphorus pentoxide
Dinitrogen monoxide
Silicon dioxide
Carbon tetrabromide
Sulfur dioxide
Phosphorus pentabromide
Iodine trichloride
Nitrogen triiodide
Dinitrogen trioxide
Check next slide for answers

17. Answers – Write the Formula
Compound Name
Compound Formula
Carbon dioxide
CO2
Carbon monoxide CO
Diphosphorus pentoxide
P2O5
Dinitrogen monoxide
N2O
Silicon dioxide
SiO2
Carbon tetrabromide
CBr4
Sulfur dioxide
SO2
Phosphorus pentabromide
PBr5
Iodine trichloride
ICl3
Nitrogen triiodide
NI3
Dinitrogen trioxide
N2O3

18. Practice – Name the Compounds
Compound Formula
Compound Name
N2O4
SO3 NO
NO2
As2O5
PCl3
CCl4
H2O
SeF6
Check next slide for answers

19. Answers – Name the Compounds
Compound Formula
Compound Name
N2O4
dinitrogen tetroxide
SO3
sulfur trioxide NO
nitrogen monoxide
NO2
nitrogen dioxide
As2O5
diarsenic pentoxide
PCl3
phosphorus trichloride
CCl4
carbon tetrachloride
H2O
dinitrogen monoxide
SeF6
selenium hexafluoride

20. VSEPR and Molecular Geometry
Hemoglobin

21. Models
Models are attempts to explain how nature operates on the microscopic level based on experiences in the macroscopic world.
Models can be physical as with this DNA model
Models can be mathematical
Models can be theoretical or philosophical

22. Fundamental Properties of Models
A model does not equal reality.
Models are oversimplifications, and are therefore often wrong.
Models become more complicated as they age.
We must understand the underlying assumptions in a model so that we don’t misuse it.

23. VSEPR Model (Valence Shell Electron Pair Repulsion)
The structure around a given atom is determined principally by minimizing electron pair repulsions.

24. Predicting a VSEPR Structure
Draw Lewis structure.
Put pairs as far apart as possible.
Determine positions of atoms from the way electron pairs are shared
Determine the name of molecular structure from positions of the atoms.

25. Steric Number 1 1 1 atom bonded to another atom Steric No.
Basic Geometry
0 lone pair
1 lone pair
2 lone pairs
3 lone pairs
4 lone pairs 1
linear

26. Steric Number 2
2 atoms, or lone electron pairs, or a combination of the two, bonded to a central atom.
Steric No.
Basic Geometry
0 lone pair
1 lone pair
2 lone pairs
3 lone pairs 2
linear

27. Steric Number 3
3 atoms, or lone electron pairs, or a combination of the two, bonded to a central atom.
Steric No.
Basic Geometry
0 lone pair
1 lone pair
2 lone pairs
3 lone pairs 3
trigonal planar
bent / angular
linear

28. Steric Number 4
4 atoms, or lone electron pairs, or a combination of the two, bonded to a central atom.
Steric No.
Basic Geometry
0 lone pair
1 lone pair
2 lone pairs
3 lone pairs 4
tetrahedral
trigonal pyramid
bent / angular
linear

29. Steric Number 5
5 atoms, or lone electron pairs, or a combination of the two, bonded to a central atom.
Steric No.
Basic Geometry
0 lone pair
1 lone pair
2 lone pairs
3 lone pairs 5
trigonal bipyramid
sawhorse / seesaw
t-shape
linear

30. Steric Number 6
6 atoms, or lone electron pairs, or a combination of the two, bonded to a central atom.
Steric No.
Basic Geometry
0 lone pair
1 lone pair
2 lone pairs
3 lone pairs 6
Octahedral
square pyramid
square planar

31. pentagonal bipyramidal
Steric Number 7
7 atoms, or lone electron pairs, or a combination of the two, bonded to a central atom.
Steric No.
Basic Geometry
0 lone pair
1 lone pair
2 lone pairs
3 lone pairs 7
pentagonal bipyramidal
pentagonal pyramidal

32. Intermolecular Forces of Attraction

33. Intermolecular Forces
Forces that attract molecules to other molecules. These include:
Hydrogen bonding
Dipole-dipole attraction
London dispersion forces

34. Relative Magnitudes of Forces
The types of bonding forces vary in their strength as measured by average bond energy.
Strongest
Weakest
Covalent bonds (400 kcal)
Hydrogen bonding (12-16 kcal )
Dipole-dipole interactions (2-0.5 kcal)
London forces (less than 1 kcal)

35. Hydrogen Bonding
Bonding between hydrogen and more electronegative neighboring atoms such as oxygen and nitrogen
Base pairing in DNA by hydrogen bonding

36. Hydrogen Bonding in Water

37. Polarity
A molecule, such as HF, that has a center of positive charge and a center of negative charge is said to be polar, or to have a dipole moment. H F + -

38. Dipole-Dipole Attraction
Attraction between oppositely charged regions of neighboring molecules.
Dipole-dipole attraction in hydrogen chloride, a gas that is used to make hydrochloric acid

39. London (Dispersion) Forces
The weakest of intermolecular forces, these forces are proportional to the mass of the molecule
These are the only forces of attraction between completely nonpolar molecules
Large nonpolar molecules may have substantial dispersion forces, resulting in relatively high boiling points
Small nonpolar molecules have weak dispersion forces and exist almost exclusively as gases

40. London Forces in Hydrocarbons

41. Polymers

42. Definitions
Monomer - A molecule that can combine with others of the same kind to form a polymer. 
Polymer - A substance that has a molecular structure built from a large number of similar units (monomers) bonded together.

43. Carbohydrates Monomer - The simple sugars
Glucose, sucrose, fructose (and many others)
Polymer - The complex carbohydrates.
Starch and Cellulose
are long chains of simple
sugars

44. Proteins Monomer - Amino acids
There are twenty amino acids that can be used to build human proteins

45. Proteins
Polymer - When many amino acids bond together to create long chains, the polymer is called a protein (it is also called a polypeptide because it contains many peptide bonds).

46. Insulin – A Human protein

47. DNA (a nucleic acid) is a polymer

48. DNA is made of monomers called nucleotidesG

49. Polyvinyl chloride (PVC)
Plastics
Plastics are synthetic polymers
Monomer:
Vinyl
chloride
C2H3Cl
Polymer:
Polyvinyl chloride (PVC)
……[C2H3Cl]n……

50. Synthetic Polymers and Their Uses

51. Review
Go to sciencegeek.net, click chemistry reviews, unit 3, covalent bonding review