Prosser Chemistry
Unit 6
Mr. Fluharty
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Covalent Bonding &
Intermolecular Forces
Covalent Bonding Introduction
1. Observe the "potential energy curve" (p. 192 of Holt Chemistry) in answering the following questions.
a. As two atoms are moved from far apart to close together through section C of the graph, does the
potential energy of the two atoms increase or decrease? _______________ Does the stability of
the arrangement increase or decrease? _______________ Which electrostatic force (protonelectron attraction or proton-proton repulsion) would best account for this change in stability as
the atoms approach? ______________________
Explain your answer.
b. As two atoms are moved from close together to far apart through section A of the graph, does the
potential energy of the two atoms increase or decrease? ______________ Does the stability of
the arrangement increase or decrease? _______________ Which electrostatic force (protonelectron attraction or proton-proton repulsion) would best account for this change in stability as
the atoms approach? ______________________
Explain your answer.
2.
Use Table 1 on p. 193 of Holt Chemistry to answer the following questions.
a. The bond energy for two bonded atoms is _________________ (directly or inversely)
proportional to the bond length. That is, as the bond length decreases, the bond energy
_________________ and as the bond length increases, the bond energy _________________.
3.
The size of an atom (measured as the atomic radius) is a periodic property (i.e., there is a distinct
pattern of change in the atomic radius moving across a period on the periodic table or down a group).
a.
Describe the trend in atomic radius for moving from top to bottom through a group on the
periodic table (see. pp. 136 Figure 21 in Holt Chemistry).
b. Explain why this trend exists in terms of atomic structure (shell size and/or number of protons).
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Naming Covalent Compounds
Below are some compounds and their names.
CO
CO2
NI3
N2H4
N2O5
carbon monoxide
carbon dioxide
nitrogen triiodide
dinitrogen tetrahydride
dinitrogen pentoxide
1. List any patterns you can see among the formulas and their names.
2. The first element in each compound is what kind of element?__________________
3. The second element in each compound is what kind of element?________________
4. What kind of bonding is holding these compounds together?___________________
5. Write a rule for naming covalent compounds. (Use the rule for ionic compounds as a guide.)
6. Try to name these compounds.
SiO2
NO2
S2Cl2
PCl3
7. Write the formulas for the following compounds.
sulfur dioxide
nitrogen trichloride
diphosphorus pentoxide
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Naming Covalent Compounds
Directions: When a nonmetal combines with a nonmetal, use Greek prefixes to indicate the number of
atoms of each element in the compound except in the case where the first element has only one atom.
1-mono
2-di
3-tri
4-tetra
5-penta
NO2
______________________________
CO
______________________________
PF5
______________________________
AsCl3
______________________________
CF4
______________________________
SiCl4
______________________________
N2O3
______________________________
6-hexa
Write the correct chemical formula for each of the following.
Chemical Formula
dinitrogen pentoxide
carbon tetrachloride
nitrogen dioxide
sulfur dioxide
phosphorus pentaflouride
nitrogen monoxide
sulfur trioxide
nitrogen trifluoride
boron trisulfide
carbon dioxide
nitrogen triiodide
carbon tetrabromide
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Naming Covalent and Ionic Compounds Practice
Identify the following as ionic (I) or covalent compounds (C). Then name them accordingly.
I or C
1.
NaNO3
2.
Al2O3
3.
PCl5
4.
IF3
5.
LiOH
6.
Ba(NO3)2
7.
SrBr2
8.
Cu2S
9.
N2O5
10.
Fe3N2
11.
CO
Name
Identify the following as ionic (I) or covalent compounds (C). Then write the chemical formula of each.
I or C
12.
nitrogen dioxide
13.
copper (II) phosphide
14.
iron (III) sulfate
15.
boron trisulfide
16.
sulfur trioxide
17.
aluminum phosphate
18.
chromium (III) bromide
19.
calcium sulfate
20.
nitrogen trifluoride
21.
sodium hydroxide
Formula
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Electronegativity and Types of Bonds
1. Define electronegativity (see pp. 137-8 of Holt Chemistry).
2.
Electronegativity is a periodic property. Describe the trend in electronegativity for moving across a period
on the periodic table.
3.
The electronegativity of an element describes its tendency to hog electrons in a bond. The ultimate electron
hogs tend not to share their electrons with other atoms, but rather to "steal" them. This effects the tendency
of a bond to become more ionic (where electrons are transferred) and less covalent (where electrons are
shared). The greater the difference in electronegativity, the greater the ionic character of the bond. Based on
this principle, use the electronegativity chart on p. 194 of the textbook to identify the following bonds as
being a C-H bond, C-C bond, C-N bond, C-O bond, or C-F bond. The diagrams show two bonded atoms
and their electron clouds.
_________
4.
_________
_________
_________
_________
Use Figure 6 and Figure 7 on pages 195-6 in Holt Chemistry to fill in the electronegativity of each element
and to classify each bond as being ionic, nonpolar covalent, or polar covalent
Bond
A-B
Electronegativity
of Element A
Electronegativity
of Element B
Difference in
Electronegativity
Classification
of Bond
C-H
2.5
2.1
0.4
Polar Covalent
C-C
C- N
Na - Cl
Mg - O
N-H
Si - F
O-H
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Electronegativity and Bond Polarity
1. Describe the difference between a purely covalent bond and a polar covalent bond.
2. For each of the following bonds, find the electronegativity difference and indicate
whether the bond will be ionic, polar covalent, or covalent.
bonded elements
electronegativity difference
type of bond
Na -- F
H -- O
H -- H
C -- H
N -- O
3. For each of the following, circle the pair which would form a more polar bond.
a. H -- Cl or H -- I
b. N -- P or N -- O
c. H -- O or H -- N
d. N -- S or N -- C
e. H -- P or H -- S
4. In each of the following molecules, label the atoms to show which has a partial positive and a
partial negative charge.
a.
H -- Cl
b.
C -- O
c.
O -- N
5. HF has a polar covalent bond. What does that tell us about the electrons involved in the bond?
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Electronegativity and Bond Polarity
6. Use your electronegativity chart to identify the diagrams below as being one of the following:
C - H bond
C - C bond
C - N bond
C - O bond
C - F bond
Each diagram shows two bonded atoms and their electron clouds.
_________
_________
_________
_________
_________
Guidelines for Drawing Lewis Structures
1. Count the total number of valence electrons in the compound.

If you are finding the structure of an ion, remember to add electrons for a negative charge
and subtract electrons for a positive charge.
2. Predict the arrangement of the atoms in the molecule, drawing a line to represent a single
bond between each pair of bonded atoms.


The first atom listed in the formula is usually the central atom.
Remember that H can only be bonded to one other atom.
3. Find the number of valence electrons left over after forming the single bonds. Remember that
each single bond you drew counts for two electrons.
4. Place electrons around the outside atoms until each is surrounded by eight electrons (The
octet rule). Remember that H does not follow the octet rule. It will only have two electrons.
5. Place any leftover electrons around the central atom. Note: it is ok to have more than eight
electrons—even though this violates the octet rule—around the central atom if the atom is
from the third row or lower on the periodic table. (The reason is that the element is filling d
orbitals.)
6. Double & Triple Bonds: If there are not enough electrons to put eight around the central
atom, go back and change one or more of the single bonds to double or triple bonds. Double
or triple bonds are most commonly formed between C, N, O, and S.
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Drawing Lewis Structures
1. Describe what holds a pair of atoms together in a covalent bond.
2. Complete the following table.
element
# of valence electrons
Lewis dot structure
# of bonds possible
carbon
nitrogen
fluorine
neon
3. Draw the Lewis structures for the following molecules and ions.
formula
Lewis structure
formula
SO32SiH4
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Lewis structure
Lewis Structures Part 2 (cont.)
CO32NF3
CO
NO2+
CS2
H2O
HCl
SO2
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Lewis Structures Part 2
1. In which of the following drawings does the atom A violate the octet rule?
a)
A
d)
..
A
g)
A
b)
..
A
e)
:A
h)
..
A
..
c)
..
A
..
f)
A
i)
..
A
2. Which of the following elements are allowed to violate the octet rule by being surrounded by
more than eight electrons?
a. C
b. P
c. Se
d. O
e. Be
f. Te
g. F
h. S
3. Draw the Lewis structures for the following molecules and ions.
formula
Lewis structure
formula
PH3
SeF2
PO43SO3
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Lewis structure
Lewis Structures Part 2 (cont.)
CH2Cl2
(C is the
central atom)
HCN
XeF4
O3
C2H2
SF4
(The C
atoms are
bonded to
each other)
OF2
HCO2 -
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Lewis Structures Part 3
1. Draw the Lewis structures for the following molecules and ions.
formula
Lewis structure
formula
BrO3-
SCN-
HCO2 -
OCl2
carbon
tetrachloride
Carbon
tetrafluoride
bromine
trifluoride
Nitrogen
trifluordide
2. Name the group of elements that X would belong to.
.
.
b. X
.
c. .
...X...
a.
X
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Lewis structure
Molecular Shapes Part 1
Determine the Lewis structure of each molecule and use the VSEPR Table to draw and name the
3-dimmensional molecular shape.
molecule
Lewis
structure
shape
drawing
CS2
ClO2+
SO3
SeO2
SCN -
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name of
shape
Molecular Shapes Part 2
Determine the Lewis structure of each molecule and use the VSEPR Table to draw and name the
3-dimmensional molecular shape.
molecule
Lewis
structure
shape
drawing
CCl4
SCl2
H2CO
C is the
central
atom
PF3
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name of shape
Molecular Shapes Part 3
Determine the Lewis structure of each molecule and use the VSEPR Table to draw and name the
3-dimmensional molecular shape.
molecule
Lewis
structure
shape
drawing
SnCl3-
SnCl4
SO32-
HCN
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name of shape
Molecular Shapes Part 3
molecule
Lewis
structure
shape
drawing
name of shape
O3
CO32-
2. Use the choices below to indicate the value closest to the true value for the bond angles
represented in the following Lewis structures.
= 90°
= 109.5°
= 120°
= 180°
a.
a
H
H
C
H
H
d
H
C
b
N
..
c
..
O
..
b.
H
c.
H
d.
H
..
N
e
C
C
H
H : O:
f
..
O
..
f.
H : O: H
C
h
C C
H
C
C
g
H
i
C
e.
H
g.
..
Cl
.. :
h.
i.
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Polarity of Molecules
1. Fill in the table below.
Lewis structure
Shape drawing
contains polar
bonds?
molecule is
symmetric?
molecule is
polar?
CS2
yes / no
yes / no
yes / no
H2S
yes / no
yes / no
yes / no
CCl4
yes / no
yes / no
yes / no
NH3
yes / no
yes / no
yes / no
SO2
yes / no
yes / no
yes / no
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Polarity of Molecules (cont.)
2. For each of the following molecules:
molecule
Draw the Lewis structure.
Draw and name the molecular shape.
Decide if the molecule is polar or nonpolar.
If the molecule is polar, label the positive side (+)
and negative side ( -).
Lewis
structure
shape
drawing
polar or
nonpolar?
H2O
yes / no
PBr3
yes / no
SO3
yes / no
CH3F
yes / no
C is the
central
atom
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