Announcements & Agenda (01/31/07)
This week’s quiz moved to Friday (Ch 4)
Exam NEXT FRIDAY!!!




Covers Ch 1-5
Intermolecular Forces (Notes + bits & pieces of Ch 6)
Ch 7.1-7.3
CHM 103 Lab
Today
 Molecular Shapes & Polarity (4.7)
 Chemical Reactions (5.1-5.3)
1
Last Time: Covalent Bonding
2
Flowchart for Naming Compounds
3
Learning Check
Classify as ionic or covalent compounds, then name ’em.
A. Ca3(PO4)2 ionic
B. FeBr3
ionic
Ca2+ PO43−
calcium phosphate
Fe3+ Br −
iron(III) bromide
C. SCl2
covalent
1S 2 Cl
sulfur dichloride
D. Cl2O
covalent
2 Cl 1 O
dichlorine monoxide
E. N2
covalent
2N(element) nitrogen
4
Connecting the Extremes: In Between
Ionic and Covalent Bonds (4.6)
A pure covalent bond occurs only when
two identical atoms are bonded: N2
Polar Covalent Bond: Unequal sharing
between two dissimilar atoms


Therefore, the electrons are nearer to one of
the atoms, and that atom acquires a partial
negative charge (d-).
And consequently the other atom has a partial
positive charge (d+).
5
Some Electronegativity Values for
Group A Elements
Electronegativity` increases
Electronegativity decreases
High
values
`
Low
values
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Publishing as Benjamin Cummings
6
The Two Extremes Revisited…
The greater the difference of the EN values, the
more polar the bond! An EN difference ≥ 1.8 is
considered an ionic bond.
7
Nonpolar Covalent Bonds
• occur between nonmetals.
• have equal or almost equal sharing of electrons.
• have almost no electronegativity difference (0.0 to 0.4).
Examples:
Atoms
N-N
Cl-Br
H-Si
Electronegativity
Difference
3.0 - 3.0 = 0.0
3.0 - 2.8 = 0.2
2.1 - 1.8 = 0.3
Type of Bond
Nonpolar covalent
Nonpolar covalent
Nonpolar covalent
8
Polar Covalent Bonds
• occur between nonmetal atoms.
• have an unequal sharing of electrons.
• have a moderate electronegativity difference (0.5 to 1.7).
Examples:
Atoms
O-Cl
Cl-C
O-S
Electronegativity
Difference
3.5 - 3.0 = 0.5
3.0 - 2.5 = 0.5
3.5 - 2.5 = 1.0
Type of Bond
Polar covalent
Polar covalent
Polar covalent
9
Ionic Bonds
• occur between metal and nonmetal ions.
• form as a result of electron transfer.
• have a large electronegativity difference (1.8 or more).
Examples:
Atoms
Cl-K
N-Na
S-Cs
Electronegativity
Difference
3.0 – 0.8
= 2.2
3.0 – 0.9
= 2.1
2.5 – 0.7
= 1.8
Type of Bond
Ionic
Ionic
Ionic
10
Shapes & Polarity of Molecules (4.7)
11
Shapes of Molecules
3-D shape affected by the # of atoms and
lone pairs around the central atom

determine from Lewis Dot Structures
Use VSEPR theory (valence-shell-electronpair repulsion
12
Using the VSEPR Model
1. Draw the electron-dot structure
2. Count the total # of electron pairs (groups)
around central atom
•
IMPORTANT: INCLUDES BOTH LONE PAIRS AND
BONDED ATOMS!!!
3. Predict the electron group geometry (EGG)
4. Predict the shape of the molecule using the # of
ATOMS bonded to the central atom
13
Four Electron Groups
In a molecule of CH4,
• there are 4 electron groups
around C.
• repulsion is minimized by
placing four electron groups at
angles of 109°, which is a
tetrahedral arrangement.
• the shape with four bonded
atoms is tetrahedral.
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
14
Three Bonding Atoms & 1 Lone Pair
In a molecule of NH3,
• 3 electron groups bond to H atoms and the 4 one is a
lone (nonbonding) pair.
• repulsion is minimized with 4 electron groups in a
tetrahedral arrangement.
• with three bonded atoms, the shape is pyramidal.
15
2 Bonding Atoms & 2 Lone Pairs
In a molecule of H2O,
• two electrons groups are bonded to H atoms and two are
lone pairs (4 electron groups).
• four electron groups minimize repulsion in a tetrahedral
arrangement.
• the shape with two bonded atoms is bent(~109).
16
Shapes with 4 Electron Groups
Electron
Group
Bonded Lone Bond
Molecular
Atoms Pairs Angles Shape
Example
4
4
0
109
tetrahedral CH4
4
3
1
~109
Pyramidal NH3
4
2
2
~109
Bent
H 2O
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Publishing as Benjamin Cummings
17
Learning Check
State the number of electron groups, lone pairs, and
use VSEPR theory to determine the shape of the
following molecules or ions.
1) tetrahedral
2) pyramidal
3) bent
A. PF3
B. H2S
C. CCl4
18
Solution
A. PF3
4 electron groups, 1 lone pair, (2) pyramidal
B. H2S
4 electron groups, 2 lone pairs, (3) bent
C. CCl4
4 electron groups, 0 lone pairs, (1) tetrahedral
19
Polar Molecules
• contain polar bonds.
• have a separation of positive and negative
charge called a dipole indicated with d+ and d-.
• have dipoles that do not cancel!
d+ d-
••
H–Cl
H—N—H
dipole
H
dipoles do not
cancel
20
Nonpolar Molecules
A nonpolar molecule
• contains nonpolar bonds.
Cl–Cl
H–H
• or has a symmetrical arrangement of polar bonds.
O=C=O
Cl
Cl–C–Cl
Cl
dipoles cancel
21
Determining Molecular Polarity
STEP 1:
STEP 2:
STEP 3:
Write the electron-dot formula.
Determine the polarity of the bonds.
Determine if dipoles cancel.
Example:
H2O
..
H─O:
H2O is polar
│
H
dipoles do not cancel
22
Learning Check
Identify each of the following molecules as
1) polar or 2) nonpolar.
A.
HBr
B.
Br2
C.
SiBr4
23
Solution
Identify each of the following molecules as
1) polar or 2) nonpolar.
A.
HBr
linear; one polar bond (dipole); polar
B.
Br2
linear; nonpolar bond; nonpolar
C.
SiBr4 tetrahedral; dipoles cancel; nonpolar
24
A couple more keypad questions to
close out Chapter 4.
25
What type of bond would form between
a Carbon atom and an Oxygen atom?
1.
2.
3.
4.
0%
0%
0%
0%
1
2
3
4
Nonpolar covalent
Polar covalent
Ionic
C and O can’t ever form bonds
5
26
In a molecule of Oxygen (O2), the
atoms are joined by a:
1.
2.
3.
4.
0%
0%
0%
0%
1
2
3
4
Single bond
Double bond
Triple bond
Quadruple bond
5
27
Chapter 5!!!
Chemical Reactions
28
Chemical Change
• reacting substances
form new
substances with
different
compositions and
properties.
• a chemical reaction
takes place.
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Publishing as Benjamin Cummings
29
Physical Change
• the identity and
composition of the
substance do not
change.
• the state can
change or the
material can be torn
into smaller pieces.
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
30
Examples of Chemical and
Physical Changes
31
Chemical Reaction
• old bonds are broken
& new bonds are
formed.
• atoms in the reactants
are rearranged to form
one or more different
substances.
• Fe and O2 form rust
(Fe2O3).
32
Chemical Equations
Gives the chemical formulas of the reactants on
the left of the arrow and the products on the right.
Reactants
O2 (g)
C(s)
Product
CO2 (g)
33
Symbols Used in Equations
• the states of the
reactants.
TABLE 5.2
• the states of the
products.
• the reaction
conditions.
34
Chemical Equations are Balanced
In a balanced
chemical
reaction
• atoms are not
gained or lost.
• the # of reactant
atoms is equal to
the number of
product atoms.
35
Quick check….
Determine if each equation is balanced or not.
A. Na(s) + N2(g)  Na3N(s)
No. 2 N on reactant side, 1 N on product side.
1 Na on reactant side, 3 Na on product side.
B. C2H4(g) + H2O(l)  C2H5OH(l)
Yes. 2 C
= 2C
6H
= 6H
1O
= 1O
36
Guide to Balancing a Chemical
Equation:
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Education, Inc.
Publishing as Benjamin Cummings
37
Steps in Balancing an Equation
To balance the following equation,
Fe3O4(s) + H2(g)  Fe(s) + H2O(l)
• work on one element at a time.
• use only coefficients in front of formulas.
• do not change any subscripts.
Fe:
Fe3O4(s) + H2(g)  3Fe(s) + H2O(l)
O:
Fe3O4(s) + H2(g)
 3Fe(s)
+ 4H2O(l)
H:
Fe3O4(s) + 4H2(g)  3Fe(s)
+ 4H2O(l)
38
Balancing Chemical Equations
1. Write the equation with the correct formulas.
NH3(g) + O2(g)
 NO(g) + H2O(g)
2. Determine if the equation is balanced.
No, not all atoms are balanced.
3. Balance with coefficients in front of formulas.
4NH3(g) + 5O2(g)  4NO(g) + 6H2O(g)
4. Check that atoms of each element are equal in reactants
and products.
4 N (4 x 1 N)
=
4 N (4 x 1 N)
12 H (4 x 3 H)
=
12 H (6 x 2 H)
10 O (5 x 2 O)
=
10 O (4 O + 6 O)
39
Equations with Polyatomic Ions
40
Balancing with Polyatomic Ions
MgCl2(aq) + Na3PO4(aq)  NaCl(aq) + Mg3(PO4)2(s)
Balance PO43- as a unit
MgCl2(aq) + 2Na3PO4(aq)  NaCl(aq) + Mg3(PO4)2(s)
2 PO43=
2 PO43Balance Mg and Cl
3MgCl2(aq) + 2Na3PO4(aq)  6NaCl(aq) + Mg3(PO4)2(s)
3 Mg2+
=
3 Mg2+
6 Na+
=
6 Na+
6 Cl=
6 Cl41