James T. Shipman
Jerry D. Wilson
Charles A. Higgins, Jr.
Omar Torres
Chapter 12
Chemical Bonding
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Lewis Symbols
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Section 12.4
Drawing Lewis Structures
A molecular representation that shows both the connections
among atoms and the locations of lone-pair valence electrons
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Lewis structure of NF3
Step 1 – Count valence electrons) = 26 valence electrons
Step 2 – Draw a skeletal structure
Step 3 – connect atoms using single bonds
Step 4 - starting with outermost atoms distribute the remaining
electrons to satisfy octet, you may need to double or triple
the bonding. After satisfying the octet, position any extra
electrons onto the central atom
F
N
F
F
Lewis Structure: NH3
NH3 = 8e-
H
N
H
H
Lewis Structure: H2O
H2O = 8e-
H
O
H
Lewis Structure : PCl3
Lewis Structure : SO2
VSEPR models: Arrangement of Electron Pairs
Linear
Trigonal Planar
Tetrahedral
9
Molecular shape
1.
2.
3.
4.
Draw the Lewis structure .
Count the bonding and nonbonding pairs of electrons
Select the corresponding VSEPR models
Molecular shape is derived by considering the positions
of bonded atoms.
Molecular Shape:
NH3
Lewis Structure
NH3 = 8eMolecular Geometry
H
N
H
H
Molecular Shape: H2O
Lewis Structure
H2O = 8eMolecular Geometry
H
O H
Molecular Shape:
SO2
Molecular Shape:
HCN
Molecular Shape:
CO2
Molecular Shape:
CH2O
Electronegativity
Electronegativity (EN) – the ability of an atom in a
molecule to draw bonding electrons to itself
Bond Polarity
3.0 - 3.0 = 0
Bond is non-polar
3.0 – 2.1 = 0.9
Bond is polar
18
Polar Molecules
Molecular polarity is due to individual bond polarities and
lone-pair contributions. Electrons are displaced toward the
more electronegative atom.
Molecular Polarity
Ionic Bonding
An electrostatic attraction between oppositely charged ions
occurs between metals and nonmetals
Naming Ions
Main group metal cations
are named by identifying the metal, followed by the word
“ion.”
Example:
Naming Ions
Transition metals cations
The charge on the ion is given as a Roman numeral (I, II,
III,…) in parentheses right after the metal name
Naming Ions
Anions
are named by replacing the ending of the element name with
-ide, followed by the word “ion.”
Naming Ions
Polyatomic ions
Are composed of more than one atom. They are charged because
they contain a total number of electrons that is different from the
total number of protons in the combined atoms.
Naming Ionic Compounds
• Type I ionic compounds contain cations of
main group elements. The charges on these
cations are unique and are known based on their
position in the periodic table.
NaCl :
Sodium Chloride
MgCl2 :
Magnesium Chloride
Naming Ionic Compounds
Alkali & Alkali earth Metals
1. NaNO2 :
Sodium Nitrite
3. MgCl2 :
Magnesium Chloride
4. Mg(NO3)2: Magnesium Nitrate
5. BaO:
Barium Oxide
6. Li3N:
lithium Nitride
3-
Naming Ionic Compounds
• Type II ionic compounds contain transition
metals that can exhibit more than one charge
– Specify the charge on the cation in these
compounds with (Roman Numerals) system. The
charges on the cations are known by looking at
bonding anions:
FeCl2:
Iron(II) Chloride
FeCl3 :
Iron(III) Chloride
Name the following ionic compounds
1. PbCl2
2. Mg3(PO4)2
3. SnO2
4. Ca3N2
Covalent Bonding
Sharing of electrons
• Based on their formulas, which of the following
are ionic compounds? Which are molecular
compounds?
1. O2 – molecular compound
2. CaO – ionic compound
3. Na3N – ionic compound
4. NF3 – molecular compound
3-
Naming Molecular Compounds
• The prefix mono-, meaning one, is omitted except
where needed to distinguish between two different
compounds with the same elements, such as carbon
monoxide and carbon dioxide.
Naming Molecular Compounds
Naming Molecular Compounds
HI
hydrogen iodide
NF3
nitrogen trifluoride
SO2
sulfur dioxide
N2Cl4
dinitrogen tetrachloride
NO2
nitrogen dioxide
N2O
dinitrogen monoxide
Naming Molecular Compounds
SO2 :
Sulfur dioxide
NF3:
Nitrogen trifluoride
P4O10 :
Tetraphosphorus decoxide
OF2 :
Oxygen difluoride
SiCl4 :
Silicon tetrachloride
P4O6:
Tetraphosphorus hexoxide
Calculating Formula Masses
• Find the formula mass (FM) of lead chromate,
PbCrO4 – used for yellow lines on streets
• Using the Periodic Table, look up the atomic masses
of Pb, Cr, and O
• Pb (207.2 u), Cr (52.0 u), O (16.0 u)
• Formula Mass = 207.2 u + 52.0 u + (4 × 16 u)
• FM of PbCrO4 = 323.2 u
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Section 12.2
Calculating Percentage
by Mass of an Element
mass of component X
100%
• %X by mass =
formula mass of compound
• H2O for example:
Section 12.2
16 u
• %O by mass =
100%  88.9%
18 u
• %H by mass = 11.1% (the remainder)
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Calculating Percentage
by Mass for CO2
• “Dry Ice” is solid CO2
• AM (atomic mass) of C = 12.0 u & O = 16.0 u
• FM (formula mass) of CO2 =
12.0 u + (2×16.0 u) = 44.0 u
• % mass of C = (Mc/FMCO2)×100 = ???%
• % mass of C = (12.0 u/44.0 u)×100 = 27.3%
• Since the % mass of C = 27.3%
• \ the % mass of O = 72.7%
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Section 12.2
Number of Covalent Bonds
Expected by Common Nonmetals
Exceptions are uncommon in Periods 1 & 2, but occur with more frequency
starting with Period 3
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Section 12.5
Homework
Exercises
3
13
14
15
16
19
21
23
24
27
28
29
30
31
32
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