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7.2 Ionic Bonds and Ionic Compounds >
Chapter 7
Ionic and Metallic Bonding
7.1 Ions
7.2 Ionic Bonds and
Ionic Compounds
7.3 Bonding in Metals
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7.2 Ionic Bonds and Ionic Compounds >
CHEMISTRY
& YOU
Where does table salt come from?
In some countries,
salt is obtained by
the evaporation of
seawater. In other
countries, salt is
mined from rock
deposits deep
underground.
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7.2 Ionic Bonds and Ionic Compounds > Formation of Ionic
Compounds
Element = a combinations of identical atoms
Mixture = a combination of two or more
elements that can be easily separated
Compound = a combination of two or more
elements chemically combined and difficult to
separate
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7.2 Ionic Bonds and Ionic Compounds > Formation of Ionic
Compounds
• An ionic compound is composed of
cations and anions.
 Metal and non-metal combination
 Left side of the stair-step line with the right
side of the line
Sodium chloride, or table salt, is an
ionic compound consisting of sodium
cations and chloride anions.
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7.2 Ionic Bonds and Ionic Compounds > Formation of Ionic
Compounds
Formation of Ionic Compounds
What is the electrical charge of an
ionic compound?
5
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7.2 Ionic Bonds and Ionic Compounds > Formation of Ionic
Compounds
Although they are composed of ions,
ionic compounds are electrically
neutral.
• The total positive charge of the
cations equals the total negative
charge of the anions.
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7.2 Ionic Bonds and Ionic Compounds > Formation of Ionic
Compounds
Ionic Bonds
Cations and anions have opposite
charges and attract one another.
• The electrostatic forces that hold ions
together in ionic compounds are called
ionic bonds.
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7.2 Ionic Bonds and Ionic Compounds > Formation of Ionic
Compounds
Ionic Bonds
When sodium and chlorine react, the sodium
atom transfers its one valence electron to the
chlorine atom.
• Sodium and chlorine atoms combine in a one-toone ratio, and both ions have stable octets.
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Formation of Ionic
Compounds
Ionic Bonds
Aluminum metal (Aℓ) and
the nonmetal bromine (Br2)
react violently to form the
ionic solid aluminum
bromide (AℓBr3).
• Each bromine atom has seven
valence electrons and readily
gains one additional electron.
• Three bromine atoms
combine with each aluminum
atom.
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7.2 Ionic Bonds and Ionic Compounds > Formation of Ionic
Compounds
Formula Units
A chemical formula shows the
numbers of atoms of each element in
the smallest representative unit of a
substance.
• NaCℓ is the chemical formula for sodium
chloride.
The chemical formula of an ionic compound refers
to a ratio known as a formula unit.
• A formula unit is the lowest wholenumber ratio of ions in an ionic compound.
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7.2 Ionic Bonds and Ionic Compounds > Formation of Ionic
Compounds
Formula Units
For sodium chloride, the lowest wholenumber ratio of the ions is 1:1 (one
Na+ ion to each Cℓ– ion).
• The formula unit for sodium chloride is NaCℓ.
• Although ionic charges are used to derive the
correct formula, they are not shown when
you write the formula unit of the compound.
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7.2 Ionic Bonds and Ionic Compounds >
Sample Problem
Predicting Formulas of Ionic Compounds
Use Lewis dot structures to
predict the formulas of the ionic
compounds formed from the
following elements:
a. potassium and oxygen
b. magnesium and nitrogen
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Sample Problem
1 Analyze Identify the relevant concepts.
• Atoms of metals lose valence electrons
when forming an ionic compound.
• Atoms of nonmetals gain electrons.
• Enough atoms of each element must be
used in the formula so that electrons lost
equal electrons gained.
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7.2 Ionic Bonds and Ionic Compounds >
Sample Problem
2 Solve Apply the concepts to this problem.
a. Start with the atom’s Lewis Structures.
••
••
•
K and • O
•
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Sample Problem
2 Solve Apply the concepts to this problem.
a. In order to have a completely filled valence
shell, the oxygen atom must gain two
electrons. These electrons come from two
potassium atoms, each of which loses one
electron.
K•
•O
•
••
2–
••
••
••
K•
+
••
K+
O
K+
••
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7.2 Ionic Bonds and Ionic Compounds >
Sample Problem
2 Solve Apply the concepts to this problem.
a. Express the Lewis Structure as a
formula.
K•
K+
2–
••
••
O
••
••
••
K•
+
••
• O•
K+
• The formula of the compound formed is
K2O.
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7.2 Ionic Bonds and Ionic Compounds >
Sample Problem
2 Solve Apply the concepts to this problem.
b. Start with the atom’s Lewis Structure.
•
••
•
Mg and • N
•
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•
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Sample Problem
2 Solve Apply the concepts to this problem.
b. Each nitrogen atom needs three electrons
to have an octet, but each magnesium
atom can lose only two electrons. Three
magnesium atoms are needed for every
two nitrogen atoms.
•
•
Mg
•
•
Mg2+
• N•
••
N
••
3–
••
N
••
3–
••
••
Mg
+
••
•
•
• N•
Mg2+
••
••
•
•
••
Mg
Mg2+
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7.2 Ionic Bonds and Ionic Compounds >
Sample Problem
2 Solve Apply the concepts to this problem.
b. Express the Lewis Structure as a
formula.
• The formula of the compound formed is
Mg3N2.
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Use electron dot structures to
determine the formula of the ionic
compound formed when calcium
reacts with fluorine.
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Use electron dot structures to
determine the formula of the ionic
compound formed when calcium
reacts with fluorine.
Ca
Ca2+
–
••
F
••
–
••
••
••
••
F
•
••
•
+
••
F
••
••
••
•
••
••
••
F
•
CaF2
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7.2 Ionic Bonds and Ionic Compounds > Properties of Ionic
Compounds
Properties of Ionic Compounds
What are three properties of
ionic compounds?
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7.2 Ionic Bonds and Ionic Compounds > Properties of Ionic
Compounds
1.) Most ionic compounds are
crystalline solids at room temperature.
• The component ions in such crystals
are arranged in repeating threedimensional patterns.
The beauty of
crystalline solids
comes from the
orderly arrangement of
their component ions.
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7.2 Ionic Bonds and Ionic Compounds > Properties of Ionic
Compounds
Each ion is attracted strongly to each of its
neighbors, and repulsions are minimized
resulting in a very stable structure.
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7.2 Ionic Bonds and Ionic Compounds > Properties of Ionic
Compounds
Ionic compounds do not exist as discrete units, but as
collections of positively and negatively charged ions
arranged in repeating patterns.
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7.2 Ionic Bonds and Ionic Compounds > Properties of Ionic
Compounds
2.) Ionic compounds generally have
high melting points.
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7.2 Ionic Bonds and Ionic Compounds > Properties of Ionic
Compounds
The coordination number of an ion is the
number of ions of opposite charge that
surround the ion in a crystal.
• In NaCℓ, each ion has a
coordination number of 6.
– The coordination number of
Na+ is 6 because each Na+ ion
is surrounded by six Cℓ– ions.
– The coordination number of Cℓ–
is also 6 because each Cℓ– ion
is surrounded by six Na+ ions.
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7.2 Ionic Bonds and Ionic Compounds > Properties of Ionic
Compounds
In CsCℓ, each ion has a coordination
number of 8.
• Each Cs+ ion is
surrounded by
eight Cℓ– ions.
• Each Cℓ– ion is
surrounded by
eight Cs+ ions.
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7.2 Ionic Bonds and Ionic Compounds > Properties of Ionic
Compounds
Titanium dioxide (TiO2), or rutile,
forms tetragonal crystals.
• The coordination
number for the cation
(Ti4+) is 6.
– Each Ti4+ ion is surrounded
by six O2– ions.
• The coordination number
of the anion (O2–) is 3.
– Each O2– ion is surrounded
by three Ti4+ ions.
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7.2 Ionic Bonds and Ionic Compounds > Properties of Ionic
Compounds
3.) Ionic compounds can conduct an
electric current.
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7.2 Ionic Bonds and Ionic Compounds > Properties of Ionic
Compounds
When sodium chloride is melted, the orderly
crystal structure breaks down.
Power source
Flow of
electrons
Current meter
• If a voltage is
Flow of
Inert metal
applied across
electrons
electrodes
this molten
Cl
Na
mass, cations
migrate freely
to one
electrode and
anions migrate
To (+)
To (–)
to the other.
electrode
electrode
• This movement of electrons allows electric current to
flow between the electrodes through an external wire.
–
+
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Properties of Ionic
Compounds
This solar facility uses molten NaCℓ for its ability
to absorb and hold a large quantity of heat,
which is used to generate electricity.
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7.2 Ionic Bonds and Ionic Compounds > Properties of Ionic
Compounds
Ionic compounds also conduct electric
current if they are dissolved in water.
• When dissolved, the ions are free to move
about in the solution.
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When can ionic compounds conduct
an electric current?
A. Only when melted
B. When melted or dissolved in water
C. Only when dissolved in water
D. When solid or melted
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When can ionic compounds conduct
an electric current?
A. Only when melted
B. When melted or dissolved in
water
C. Only when dissolved in water
D. When solid or melted
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7.2 Ionic Bonds and Ionic Compounds > Key Concepts
Although they are composed of ions, ionic
compounds are electrically neutral.
1.) Most ionic compounds are crystalline
solids at room temperature.
2.) Ionic compounds generally have high
melting points.
3.) Ionic compounds can conduct an
electric current when melted or dissolved
in water.
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7.2 Ionic Bonds and Ionic Compounds >
END OF 7.2
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