Chapter 4
Compounds and Their Bonds
Covalent Bonds
4.5 Covalent Bonds
ƒ Covalent bonds form between two
nonmetals from Groups 4A, 5A, 6A, and
7A.
ƒ In a covalent bond, electrons are shared to
complete octets.
4.6 Naming and Writing Formulas of
Covalent Compounds
4.7 Bond Polarity
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Learning Check
Solution
Indicate whether a bond between the
following is 1) Ionic 2) Covalent
Indicate whether a bond between the
following is 1) Ionic 2) Covalent
____A. sodium and oxygen
____B. nitrogen and oxygen
1
2
A.
B.
sodium and oxygen
nitrogen and oxygen
____C. phosphorus and chlorine
2
C.
phosphorus and chlorine
____D. calcium and sulfur
1
D.
calcium and sulfur
____E. chlorine and bromine
2
E.
chlorine and bromine
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1
H2, A Covalent Molecule
„
„
Diatomic Elements
In hydrogen, two hydrogen atoms share their
electrons to form a covalent bond.
Each hydrogen atom acquires a stable outer
shell of two (2) electrons like helium (He).
H• + •H
H : H = H−H = H2
„
As elements,
the following
share electrons
to form
diatomic,
covalent
molecules.
hydrogen molecule
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Learning Check
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Solution
What is the name of each of the following diatomic
molecules?
hydrogen
H2
nitrogen
N2
Cl2
_______________
_______________
O2
I2
_______________
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Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
What are the names of each of the following diatomic
molecules?
H2
hydrogen
N2
nitrogen
chlorine
Cl2
O2
oxygen
I2
iodine
7
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2
Covalent Bonds in NH3
„
Number of Covalent Bonds
„
The compound NH3 consists of a N atom and three
H atoms.
•
••
Often, the number of covalent bonds formed
by a nonmetal is equal to the number of
electrons needed to complete the octet.
N • and 3 H •
•
„
By sharing electrons to form NH3, the electron dot
structure is written as
H
Bonding pairs
••
H:N:H
••
Lone pair of electrons
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Dot Structures and Models of
Some Covalent Compounds
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Multiple Bonds
ƒ Sharing one pair of electrons is a single bond.
X:X
or
X–X
ƒ In multiple bonds, two pairs of electrons are
shared to form a double bond or three pairs
of electrons are shared in a triple bond.
X:
:X
X:::X
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or
X =X
or
X≡X
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3
Multiple Bonds in N2
„
„
•
Naming Covalent Compounds
In the name of a
covalent compound,
the first nonmetal is
named followed by
the name of the
second nonmetal
ending in –ide.
ƒ Prefixes indicate the
number of atoms of
each element.
„
In nitrogen, octets are achieved by sharing
three pairs of electrons.
When three pairs of electrons are shared, the
multiple bond is called a triple bond.
octets
••
N•
+ •
•
••
N•
•
⎯→
••
••
N:::N
triple bond
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Learning Check
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Solution
Complete the name of each covalent compound:
Complete the name of each covalent compound:
CO
carbon ______oxide
CO
carbon monoxide
CO2
carbon _______________
CO2
carbon dioxide
PCl3
phosphorus ___________
PCl3
phosphorus trichloride
CCl4
carbon _______________
CCl4
carbon tetrachloride
N2O
______________________
N2O
dinitrogen monoxide
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4
Formulas and Names of Some
Covalent Compounds
Learning Check
Select the correct name for each compound.
A. SiCl4 1) silicon chloride
2) tetrasilicon chloride
3) silicon tetrachloride
B. P2O5 1) phosphorus oxide
2) phosphorus pentoxide
3) diphosphorus pentoxide
C. Cl2O7 1) dichlorine heptoxide
2) dichlorine oxide
3) chlorine heptoxide
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Solution
ƒ Electronegativity is the attraction of an atom
for shared electrons.
ƒ The nonmetals have high electronegativity
values with fluorine as the highest.
ƒ The metals have low electronegativity values.
3) diphosphorus pentoxide
C. Cl2O7 1) dichlorine heptoxide
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Electronegativity
Select the correct name for each compound.
A. SiCl4 3) silicon tetrachloride
B. P2O5
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5
Some Electronegativity Values for
Group A Elements
Nonpolar Covalent Bonds
ƒ The atoms in a nonpolar covalent bond have
electronegativity differences of 0.3 or less.
ƒ Examples:
Atoms Electronegativity Type of
Difference
Bond
N-N
3.0 - 3.0 = 0.0
Nonpolar covalent
Cl-Br
3.0 - 2.8 = 0.2
Nonpolar covalent
H-Si
2.1 - 1.8 = 0.3
Nonpolar covalent
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Comparing Nonpolar and Polar
Covalent Bonds
Polar Covalent Bonds
ƒ The atoms in a polar covalent bond have
electronegativity differences of 0.4 to 1.6.
ƒ Examples:
Atoms Electronegativity Type of
Difference
Bond
O-Cl
3.5 - 3.0 = 0.5
Polar covalent
Cl-C
3.0 - 2.5 = 0.5
Polar covalent
O-S
3.5 - 2.5= 1.0
Polar covalent
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6
Ionic Bonds
Range of Bond Types
ƒ The atoms in an ionic bond have
electronegativity differences of 1.7 or more.
ƒ Examples:
Atoms Electronegativity
Type of
Difference
Bond
Cl-K
3.0 – 0.8
= 2.2
Ionic
N-Na
3.0 – 0.9
= 2.1
Ionic
S-Cs
2.5 – 0.7
= 1.8
Ionic
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Predicting Bond Type
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Learning Check
Identify the type of bond between the
following as
1) nonpolar covalent
2) polar covalent
3) ionic
A. K-N
B. N-O
C. Cl-Cl
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Chapter 4
Compounds and Their Bonds
Solution
4.8
A. K-N
3) ionic
B. N-O
2) polar covalent
C. Cl-Cl
1) nonpolar covalent
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Polyatomic Ions
„
„
Polyatomic Ions
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Common Polyatomic Ions
A polyatomic ion is a group of two or more
atoms that has an overall ionic charge.
Some examples of polyatomic ions are
NH4+
ammonium
OH -
NO3-
nitrate
NO2 - nitrite
CO32 -
carbonate
PO43 - phosphate
HCO3 -
hydrogen carbonate (bicarbonate)
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hydroxide
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8
Some Compounds with Polyatomic
Ions
Formulas with Polyatomic Ions
„
„
The formula of an ionic compound containing
a polyatomic ion is written to make the
overall charge equal zero (0).
Na+ and NO3NaNO3
When two or more polyatomic ions are
needed, the polyatomic ion is enclosed in
parentheses.
polyatomic ion
Mg2+
and NO3
-
Mg(NO3)2
subscript 2 for charge balance
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Learning Check
Select the correct formula for each:
A. Aluminum nitrate
1) AlNO3
2) Al(NO)3
B. Copper(II) nitrate
1) CuNO3
2) Cu(NO3)2
C. Iron (III) hydroxide
1) FeOH
2) Fe3OH
D. Tin(IV) hydroxide
1) Sn(OH)4 2) Sn(OH)2
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Solution
Select the correct formula for each:
A.
Aluminum nitrate
3) Al(NO3)3
B.
Copper(II) nitrate
2) Cu(NO3)2
C.
Iron (III) hydroxide
3) Fe(OH)3
D.
Tin(IV) hydroxide
1) Sn(OH)4
3) Al(NO3)3
3) Cu2(NO3)
3) Fe(OH)3
3) Sn4(OH)
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9
Naming Compounds with
Polyatomic Ions
Learning Check
ƒ For compounds with polyatomic ions, the
positive ion is named first followed by the
name of the polyatomic ion.
sodium nitrate
NaNO3
potassium sulfate
K2SO4
aluminum bicarbonate
Al(HCO3)3
or aluminum hydrogen carbonate
ammonium phosphate
(NH4)3PO4
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Match each formula with the correct name:
A. Na2CO3
1) magnesium sulfite
MgSO3
2) magnesium sulfate
MgSO4
3) sodium carbonate
B. Ca(HCO3)2
CaCO3
Ca3(PO4)2
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Solution
1) calcium carbonate
2) calcium phosphate
3) calcium bicarbonate
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Summary of Naming Compounds
A. Na2CO3
MgSO3
MgSO4
3) sodium carbonate
1) magnesium sulfite
2) magnesium sulfate
B. Ca(HCO3)2
CaCO3
Ca3(PO4)2
3) calcium bicarbonate
1) calcium carbonate
2) calcium phosphate
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Naming Rules
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Naming Rules (continued)
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Learning Check
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Solution
Name each of the following compounds:
A. Mg(NO3)2
B. CuCl2
C. N2O4
D. Fe2(SO4)3
E. Ba3(PO4)2
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Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Name each of the following compounds:
A. Mg(NO3)2
magnesium nitrate
copper(II) chloride
B. CuCl2
C. N2O4
dinitrogen tetroxide
iron(III) sulfate
D. Fe2(SO4)3
E. Ba3(PO4)2
barium phosphate
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Learning Check
Solution
Write the correct formula for each:
A. potassium sulfide
B. calcium carbonate
C. sodium phosphite
D. iron(III) oxide
E. iron (II) nitrate
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Write the correct formula for each:
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K2S
B. calcium carbonate
CaCO3
C. sodium phosphite
Na3PO3
D. iron(III) oxide
Fe2O3
E. iron (II) nitrate
Fe(NO3)2
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Chapter 4
Compounds and Their Bonds
46
VSEPR
„
4.9 Shapes of Molecules
4.10 Polar and Nonpolar Molecules
„
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A. potassium sulfide
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The shape of a molecule is predicted from the
geometry of the electrons pairs around the
central atom.
In the valence-shell electron-pair repulsion
theory (VSEPR), the electron pairs are arranged
as far apart as possible to give the least amount of
repulsion of the negatively charged electrons.
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12
Two Electron Pairs with
Double Bonds
Two Electron Pairs
„
„
„
In a molecule of BeCl2, there are two bonding
pairs around the central atom Be. (Be is an
exception to the octet rule.)
The arrangement of two electron pairs to
minimize their repulsion is 180° or opposite
each other.
The shape of the molecule is linear.
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„
„
„
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„
„
In BF3, there are 3 electron pairs around the central
atom B. (B is an exception to the octet rule.)
Repulsion is minimized by placing three electron
pairs in a plane at angles of 120°, which is a trigonal
planar arrangement.
The shape with three bonded atoms is trigonal
planar.
„
„
„
„
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Two Bonding Pairs and A
Nonbonding Pair
Three Electron Pairs
„
The electron-dot structure for CO2 consists of two
double bonds to the central atom C.
Because the electrons in a double bond are held
together, a double bond is counted as a single unit.
Repulsion is minimized when the double bonds are
placed opposite each other at 180° to give a linear
shape.
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In SO2, there are 3 electron units around the
central atom S.
Two electron units are bonded to atoms and
one electron pair is a nonbonding pair.
Repulsion is minimized by placing three
electron pairs in a plane at angles of 120°,
which is trigonal planar.
The shape with two bonded atoms is bent.
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Learning Check
Solution
The shape of a molecule of N2O (N N O) is
1) linear
The electron-dot structure uses 5 e for each N and
6 e for O (16 e total) has octets using two double
bond to the central N and one nonbonding pair.
The shape with two bonded atoms is linear.
The shape of a molecule of N2O (N N O) is
1) linear
2) trigonal planar
3) bent (120°)
••
••
: N :: N :: O :
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Three Bonding Atoms and One
Nonbonding Pair
Four Electron Pairs
„
„
„
In CH4, there are 4 electron pairs around the
central atom C.
Repulsion is minimized by placing four
electron pairs at angles of 109°, which is a
tetrahedral arrangement.
The shape with four bonded atoms is called
tetrahedral.
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„
„
„
„
55
In NH3, there are 4 electron pairs around the N.
Three pairs are bonded to atoms and one is a
nonbonding pair.
Repulsion is minimized by placing four electron
pairs at angles of 109°, which is a tetrahedral
arrangement.
The shape with three bonded atoms is pyramidal.
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14
Two Bonding Atoms and Two
Lone Pairs
„
„
„
„
Some Steps Using VSEPR to
Predict Shape
In H2O, there are 4 electron pairs around O.
Two pairs are bonded to atoms and two are
nonbonding pairs.
Repulsion is minimized by placing four
electron pairs at angles of 109° called a
tetrahedral arrangement.
The shape with two bonded atoms is called
bent.
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„
„
„
„
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Summary of Electron
Arrangements and Shapes
Draw the electron dot structure.
Count the electron pairs around the central
atom.
Arrange the electron pairs to minimize
repulsion.
Determine the shape using the number of
bonded atoms in the electron arrangement.
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Learning Check
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
D. PO43-
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Solution
Polar Molecules
Use VSEPR theory to determine the shape of
the following molecules or ions.
1) tetrahedral 2) pyramidal
3) bent
2) pyramidal
A. PF3
B. H2S
3) bent
1) tetrahedral
C. CCl4
3D. PO4
1) tetrahedral
„
„
„
A polar molecule contains polar bonds.
The separation of positive and negative
charge is called a dipole.
In a polar molecule, dipoles do not cancel.
δ+ δH–Cl
dipole
••
Cl–N–Cl
Cl
dipoles do not cancel
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Nonpolar Molecules
„
62
Learning Check
A nonpolar molecule contains nonpolar bonds
Cl–Cl
H–H
or a symmetrical arrangement of polar bonds.
O=C=O
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Identify each of the following molecules as
1) polar or 2) nonpolar. Explain.
A. PBr3
B. HBr
C. Br2
D. SiBr4
Cl
Cl–C–Cl
Cl
dipoles cancel
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Solution
Identify each of the following molecules as
1) polar or 2) nonpolar. Explain.
A. PBr3 1) polar; pyramidal
B. HBr 1) polar; polar bond
C. Br2
2) nonpolar, nonpolar bond
D. SiBr4 2) nonpolar; dipoles cancel
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