1. Chapter 7 Ionic and Metallic Bonding 7.2 Ionic Bonds and
7.1 Ions
7.2 Ionic Bonds and
Ionic Compounds
7.3 Bonding in Metals
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2. Where does table salt come from?
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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3. Formation of Ionic Compounds
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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4. 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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5. Formation of Ionic Compounds
Ionic Bonds
Anions and cations have opposite charges and attract one another by means of electrostatic forces.
The electrostatic forces that hold ions together in ionic compounds are called ionic bonds.
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6. Formation of Ionic Compounds
Ionic Bonds
When sodium and chlorine react to form a compound, the sodium atom transfers its one valence electron to the chlorine atom.
Sodium and chlorine atoms combine in a one-to-one ratio, and both ions have stable octets.
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7. 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.
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8. Formation of Ionic Compounds
Formula Units
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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9. Formation of Ionic Compounds
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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10. Formation of Ionic Compounds
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.
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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11. Predicting Formulas of Ionic Compounds
Sample Problem 7.1
Predicting Formulas of Ionic Compounds
Use electron 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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13. Use electron dot structures to determine the formula of the ionic compound formed when calcium reacts with fluorine.
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14. Properties of Ionic Compounds
What are three properties of ionic compounds?
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15. Properties of Ionic Compounds1)
Most ionic compounds are crystalline solids at room temperature.
The beauty of crystalline solids comes from the orderly arrangement of their component ions.
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16. Properties of Ionic Compounds
Each ion is attracted strongly to each of its neighbors, and repulsions are minimized.
The large attractive forces result in a very stable structure.
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17. Properties of Ionic Compounds2)
Ionic compounds generally have high melting points.
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18. Properties of Ionic Compounds3)
Ionic compounds can conduct an electric current when melted or dissolved in water.
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19. Properties of Ionic Compounds
When sodium chloride is melted, the orderly crystal structure breaks down.
To (+) electrode
To (–) electrode
Inert metal electrodes
Flow of electrons
Current meter
Power source
Cl–
Na+
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.
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20. 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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21. 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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22. 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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23. 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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24. 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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25. 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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26. END OF 7.2
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