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7.2 Ionic Bonds and Ionic Compounds >7.2 Ionic Bonds and Ionic Compounds >
1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
Chapter 7Ionic and Metallic Bonding
7.1 Ions
7.2 Ionic Bonds and Ionic Compounds
7.3 Bonding in Metals
7.2 Ionic Bonds and Ionic Compounds >7.2 Ionic Bonds and Ionic Compounds >
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CHEMISTRY & YOUCHEMISTRY & 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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Formation of Ionic Formation of Ionic CompoundsCompounds
Formation of Ionic Compounds
What is the electrical charge of an ionic compound?
7.2 Ionic Bonds and Ionic Compounds >7.2 Ionic Bonds and Ionic Compounds >
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Formation of Ionic Formation of Ionic CompoundsCompounds
Sodium chloride, or table salt, is an ionic compound consisting of sodium cations and chloride anions.
• An ionic compound is a compound composed of cations and anions.
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Formation of Ionic Formation of Ionic CompoundsCompounds
Although they are made 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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Formation of Ionic Formation of Ionic CompoundsCompounds
Ionic Bonds
• The electrostatic forces that hold ions together in ionic compounds are called ionic bonds.
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Formation of Ionic Formation of Ionic CompoundsCompounds
Ionic Bonds
• Sodium and chlorine atoms combine in a one-to-one ratio, and both ions have stable octets.
When sodium and chlorine react to form a compound, the sodium atom transfers its one valence electron to the chlorine atom.
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Formation of Ionic Formation of Ionic CompoundsCompounds
Ionic Bonds
• Each bromine atom has seven valence electrons and readily gains one additional electron.
• Three bromine atoms combine with each aluminum atom.
Aluminum metal (Al) and the nonmetal bromine (Br2) react violently to form the ionic solid aluminum bromide (AlBr3).
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Formation of Ionic Formation of Ionic CompoundsCompounds
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.
7.2 Ionic Bonds and Ionic Compounds >7.2 Ionic Bonds and Ionic Compounds >
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Formation of Ionic Formation of Ionic CompoundsCompounds
Formula UnitsIonic compounds do not exist as discrete units, but as collections of positively and negatively charged ions arranged in repeating patterns.
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Formation of Ionic Formation of Ionic CompoundsCompounds
Formula Units
The chemical formula of an ionic compound refers to a ratio known as a formula unit.• A formula unit is the lowest whole-
number ratio of ions in an ionic compound.
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Formation of Ionic Formation of Ionic CompoundsCompounds
Formula Units
For sodium chloride, the lowest whole-number ratio of the ions is 1:1 (one Na+ ion to each Cl– ion).
• The formula unit for sodium chloride is NaCl.
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Use electron dot structures to predict the formulas of the ionic compounds formed from the following elements:
Sample Problem 7.1Sample Problem 7.1
Predicting Formulas of Ionic Compounds
a. potassium and oxygen
b. magnesium and nitrogen
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a. Start with the atoms.
Solve Apply the concepts to this problem.2
Sample Problem 7.1Sample Problem 7.1
K and O •••
• •• •
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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.
Solve Apply the concepts to this problem.2
Sample Problem 7.1Sample Problem 7.1
K •
••• •• •O
K •+
K+
K+• •• •O
• •
• •
2–
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a. Express the electron dot structure as a formula.
Solve Apply the concepts to this problem.2
Sample Problem 7.1Sample Problem 7.1
• The formula of the compound formed is K2O (potassium oxide).
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b. Start with the atoms.
Solve Apply the concepts to this problem.2
Sample Problem 7.1Sample Problem 7.1
Mg and N •
• • • ••
•
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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.
Solve Apply the concepts to this problem.2
Sample Problem 7.1Sample Problem 7.1
••• • •N
• •• •N
• •
• •
3–
+ Mg2+
••• • •N
Mg2+
Mg2+
• •• •N
• •
• •
3–
Mg•
•
Mg•
•
Mg•
•
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b. Express the electron dot structure as a formula.
Solve Apply the concepts to this problem.2
Sample Problem 7.1Sample Problem 7.1
• The formula of the compound formed is Mg3N2 (magnesium nitride).
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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.
• •• •F
• •
•+ Ca2+
F• •• •• •
• •
–
Ca•
• F• •• •• •
• •
–• •• •F
• •
•
CaF2
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Properties of Ionic Properties of Ionic CompoundsCompounds
Properties of Ionic Compounds
What are three properties of ionic compounds?
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Properties of Ionic Properties of Ionic CompoundsCompounds
Most ionic compounds are crystalline solids at room temperature.
• The component ions in such crystals are arranged in repeating three-dimensional patterns.
The beauty of crystalline solids comes from the orderly arrangement of their component ions.
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Properties of Ionic Properties of Ionic CompoundsCompounds
Ionic compounds generally have high melting points.
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Properties of Ionic Properties of Ionic CompoundsCompounds
Ionic compounds can conduct an electric current when melted or dissolved in water.
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Properties of Ionic Properties of Ionic CompoundsCompounds
When sodium chloride is melted, the orderly crystal structure breaks down.
• If a voltage is applied across this molten mass, cations migrate freely to one electrode and anions migrate to the other.
• This movement of electrons allows electric current to flow between the electrodes through an external wire.
To (+) electrode
To (–) electrode
Inert metal electrodes
Flow of electrons
Flow of electrons
Current meterPower source
Cl–
Na+
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Properties of Ionic Properties of Ionic CompoundsCompounds
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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Properties of Ionic Properties of Ionic CompoundsCompounds
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
7.2 Ionic Bonds and Ionic Compounds >7.2 Ionic Bonds and Ionic Compounds >
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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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31
Questions1. What is the electrical charge on an ionic compound?
2. What is an ionic bond?
3. What does a chemical formula show?
4. Write the chemical formula for the compound that is formed when:
a. calcium reacts with oxygen
b. sodium reacts with nitrogen
c. potassium reacts with sulfur
5. What are three properties of ionic compounds?
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Glossary TermsGlossary Terms
• ionic compound: a compound composed of positive and negative ions
• ionic bond: the electrostatic attraction that binds oppositely charged ions together
• chemical formula: an expression that indicates the number and type of atoms present in the smallest representative unit of a substance
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Glossary TermsGlossary Terms
• formula unit: the lowest whole-number ratio of ions in an ionic compound; in magnesium chloride, the ratio of magnesium ions to chloride ions is 1:2 and the formula unit is MgCl2
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