2013
Chapter 8: Covalent Bonding
Section 8.1 Molecular Compounds (pg.213-216)
1. Describe the nature of a covalent bond in terms of electron sharing.
2. Identify the physical properties of molecular compounds.
3. Interpret molecular and structural formulas.
Section 8.2 The Nature of Covalent Bonding (pg. 217-229)
1. Explain the Octet Rule.
2. Understand the mechanisms of single, double, and triple bond formation.
3. Understand and mechanism and need for coordinate covalent bonding.
4. Relate the strength of a covalent bond to bond dissociation energy (supplemental # 2)
5. Recognize structural formulas that could exhibit resonance.
6. Identify exceptions to the Octet Rule.
7. Draw the structural formula for any covalently bonded molecule.
Section 8.3 Bonding Theories (pg. 230-236)
1. Define sigma and pi bonds.
2. Explain VSEPR theory.
3. Predict the shape of molecules using principle of the VSEPR theory.
4. Explain hybridization (supplemental # 4)
Section 8.4 Polar Bonds and Molecules (pg. 237-240)
1. Determine bond polarity using the electronegativity of bonded atoms.
2. Determine molecular polarity using bond polarities and the VSEPR theory.
Section 9.3 Naming and Writing Formulas for Molecular Compounds (pg. 268-270)
1. Determine the name of a molecular compound given its chemical formula
2. Determine the chemical formula of a molecular compound given its name
Written Work
Chapter 8: p. 247-250 # 40, 49, 50, 54, 56, 63, 64, 65, 66, 75, 76, 80, 85, 97
p. 251 # 2-12 even
Chapter 8 Supplemental Questions
1. Read the article “Not So Noble” (http://smellslikescience.com/not-so-noble/) Use the terms oxidation and ionization potential (energy) to provide an explanation for why XePtF6 is possible.
2. Examine the graph below and answer the questions that follow:
a. What is the relationship between the number of bonds that can exist between two atoms and the distance between those atoms (bond length)?
b. What is the relationship between bond length and the amount of energy that is required to dissociate (break) covalent bonds?
c. Linoleic acid is a fatty acid that is essential for proper growth and metabolism in humans.
a. Determine the length of the carbon backbone of one molecule of linoleic acid given its structure below and the bond lengths in the graph above.
3. Free radicals can have a negative impact on biological systems by reacting with important biomolecules like DNA.
a. Which of the exceptions to the Octet rule results in the production of free radicals?
(Go to: http://chemistry.about.com/od/chemicalbonding/tp/Exceptions-To-The-Octet-Rule.htm
to find the answer)
b. Antioxidants such as vitamin C and E “neutralize” free radicals. Oxidation is defined as the process that involves the loss of electrons in an atom and oxidizing agents accept the electrons that are lost. Likewise, reduction is a process that involves gain of electrons and reducing agents are substances that donate these electrons.
In the neutralization of a free radical by either vitamin C which of the two substances is the oxidizing agent and which substance becomes reduced? (HINT: If use NO2 as an example of a free radical and examine the definitions above, you should be able to figure this out without looking any further)
4. Watch the following video on hybridation http://www.youtube.com/watch?v=z24942I0h-8 and answer the questions that follow.
a. What would be the hybridization about the central atom for each of the following molecules?
b. Draw a molecule that exhibits sp hybridization.
Chapter 8 - Drawing Molecular Structures
Ø Use lines to represent bonding pairs of electrons
Ø Use dots to represent lone pairs of electrons
Determining the Structure of a Molecule
General Rules for Positioning Atoms
1. Hydrogen is always a terminal (end) atom which is binds to atoms other than another hydrogen (unless the molecule is H2)
2. The atom with the lowest electronegativity (more metallic character) is centered in the molecule.
Example: CO2 O=C=O
Determining the Number and Position of Electrons in a Molecule
Often, the arrangement of electrons in a molecule is obvious. Unpaired electrons in each atom form bonds between the atoms and lone pairs remain with their respective atoms. In more complex structures, lone pairs of electrons may be used in the bonding of two atoms (coordinate covalent bonding).
Obvious Covalent Bond Examples
H2 / H2O / CH4O2 / CS2 / N2
Strategy for Complex Structures
1. Determine the total amount of electrons that would be present if each atom had its own octet of electrons (exception: only two electrons for hydrogen).
2. Determine the total number of valence electron for the atoms in the molecule.
3. To determine the number of bonding pairs (electron pairs that will go between the atoms) calculate the difference between the number of electrons in step one and two and divide that number by 2.
4. Place the pairs of electrons between the atoms.
5. Add enough lone pairs to the molecule so that each atom follows the octet rule.
Structure Table
SO2 / Total Electrons / Valence Electrons / Bonding PairsCalculation / 3 atoms x 8 electrons each / (1 sulfur x 6 electrons) +
(2 oxygens x 6 electrons) / (24 -18)/2
Answer / 24 / 18 / 3
HINT: To make sure that you have bonded the atoms in the molecule correctly, make sure that each atom has a full octet (with the exception of hydrogen) and that only the amount of valence electrons were used)
Fill in the tables and draw the Lewis formula for the following compounds
CO / Total Electrons / Valence Electrons / Bonding PairsCalculation
Answer
O3 / Total Electrons / Valence Electrons / Bonding Pairs
Calculation
Answer
SO3 / Total Electrons / Valence Electrons / Bonding Pairs
Calculation
Answer
*There are three resonance structures of SO3. Draw them all.
Structural Formulas:
Lewis Structures of Polyatomic Ions
Follow the same procedure as you do for complex molecular compounds, except add a number of valence electrons equal to the charge on the ion to the total number of valence electrons in the compound (for positive ions subtract the number of electrons equal to the charge number)
Example SO42-
SO42- / Total Electrons / Valence Electrons / Bonding PairsCalculation / 5 atoms x 8 electrons each / (1 sulfur x 6 electrons) +
(4 oxygens x 6 electrons) +
2 gained electrons / (40 -32)/2
Answer / 40 / 32 / 4
Fill in the tables and draw the Lewis formula for the following compounds
PO33- / Total Electrons / Valence Electrons / Bonding PairsCalculation
Answer
NO2- / Total Electrons / Valence Electrons /
Bonding Pairs
Calculation
Answer
OH- / Total Electrons / Valence Electrons / Bonding Pairs
Calculation
Answer
For fun J
Cr2O72- / Total Electrons / Valence Electrons / Bonding PairsCalculation
Answer
Naming Molecular Compounds
Naming Rules
1. If there is more than one of the 1st atom, precede the atom name by the appropriate prefix (di, tri, tetra, penta, hexa, hepta, octa, nona, deca)
Example: C6O2 hexacarbon dioxide
2. If there is only one of the first atom, do not precede the atom name by mono.
CO2 = monocarbon dioxide CO2 = carbon dioxide
3. Precede the second atom name by the appropriate prefix, including mono if there is only one of that atom. Drop the last syllable (or 2) and add –ide to the element name
C2O Dicarbon monoxide
Element / Name / Element / NameC / Carbide / S / Sulfide
N / Nitride / Cl / Chloride
O / Oxide / Se / Selenide
F / Fluoride / Br / Bromide
P / Phosphide / I / Iodide
Provide the name of the following molecular compounds
Compound / Compound NameP6O3 / Hexaphosphorus trioxide
NS4
Se8O
C7Br5
S2F2
Provide the Chemical Formulas given the following names
Compound Name / CompoundDinitrogen monofluoride
Nonaphosphorus decachloride
Sulfur hexabromide
Tetracarbon pentasulfide
Octanitrogen trifluoride