1. Chapter 4- Chemical Compounds
8th Grade Science
Chapter 4- Chemical Compounds
© Fall 2005, Pflugerville ISD, 8th Grade

2. Chapter 4- Chemical Compounds
Section 1: Ionic Compounds
Section 2: Covalent Compounds
Section 3: Acids, Bases, & Salts
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3. What is a chemical compound?
What Do You Think?
Imagine that you need to attach two pieces of paper together. What are three ways you might do this?
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4. Unit A : Chapter 1 : Section 1
Chemical Bonds
Terms to Know:
Valence Electrons
Ionic Compounds
-Ions
-Crystal Lattice
Covalent Compounds
-Molecule
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5. Unit A : Chapter 1 : Section 1
Ionic Bonding
Ionic bonds are the forces of attraction between positive and negative ions
They are formed when atoms lend or borrow electrons from each other
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6. Unit A : Chapter 1 : Section 1
Ionic Bonding
Metals lend electrons
Nonmetals borrow electrons
Ionic compounds usually involve a metal and a nonmetal
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7. Na & Cl bond to form NaCl, or salt
Na has 1 valence electron in its outermost energy level
Cl has 7 valence electrons
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8. Na & Cl bond to form NaCl, or salt
Na lends one electron to Cl
Na becomes positive and Cl becomes negative
Salt ions are formed!
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9. Metal and Nonmetal Ions bond to form a Crystal Lattice
A crystal lattice is a 3-D, repeating pattern of ions
Ions are arranged by alternating positive and negative charges
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10. Properties of Ionic Compounds
Very high melting points
Brittle– break along planes of cleavage
Dissolve well in water
Water solution will conduct electricity
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11. Unit A : Chapter 1 : Section 1
Ionic bonds, revisited
Charged ions bond to form a neutral compound
Ionic bonds are the strongest type of bond
The number of valence electrons in an atom determines its reactivity with other elements
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12. Unit A : Chapter 1 : Section 1
Covalent Bonding
Covalent bonds are formed between nonmetals only
In a covalent bond, atoms share valence electrons
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13. Unit A : Chapter 1 : Section 1
Covalent Bonding
Valence electrons are weakly bonded to the nucleus
This weak attraction between the nuclei and the shared electron(s) binds the molecule
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O and H bond to form H2O
Oxygen has 6 valence electrons
Hydrogen has 1 valence electron
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15. Unit A : Chapter 1 : Section 1
O and H bond to form H2O
Oxygen needs 2 valence electrons for a stable shell
Hydrogen needs 1 valence electron for a stable shell
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16. Unit A : Chapter 1 : Section 1
O and H bond to form H2O
1 Oxygen bonds with 2 atoms of Hydrogen and all 3 share the electrons
As long as the electrons are shared, valence shells are full
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17. Nonmetals bond to form Molecules
The simplest type of molecule is diatomic, meaning it is made of only 2 atoms
There are only seven elements that are diatomic: Hydrogen, Oxygen, Nitrogen, Fluorine, Chlorine, Bromine, and Iodine
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18. Nonmetals bond to form Molecules
Molecules can get more complex, involving many different elements
Remember, covalent compounds contain only nonmetals
Caffeine Molecule
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19. Properties of Covalent Compounds
Low melting points
Most covalent compounds do not dissolve in water (oil & water don’t mix)
If it can dissolve, the solution does not conduct electricity
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20. Covalent bonds, revisited
Nonmetals only
Form uncharged molecules, not charged ions
Covalent bonds are the weakest type of bond
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21. Bonding & Compounds- Quick Quiz
How does a molecule form?
Which is stronger, an ionic or a covalent bond?
What is an ion?
Which type of bond typically has a higher melting point?
Which type of bond involves only nonmetals?
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22. What is a chemical compound?
What Do You Think?
Lemons and tomatoes have a tangy taste because they contain citric acid. What are some other foods that might be flavored by acids?
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23. Unit A : Chapter 1 : Section 1
What is an Acid?
All of these products contain Acids
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24. Unit A : Chapter 1 : Section 1
What is an Acid?
HCl dissolves in water because it is an ionic compound
HCl breaks apart to form H+ ions and Cl- ions
HCl is added to H2O
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25. Unit A : Chapter 1 : Section 1
What is an Acid?
The H+ ions bond with H2O to form H3O+, a hydronium ion
HCl is added to H2O
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26. Unit A : Chapter 1 : Section 1
What is an Acid?
An acid is any compound that increases the number of H+ ions when dissolved in water
These H+ ions bond with the water to create H3O+, the hydronium ion
Strong acids are corrosive, meaning they can destroy clothing and body tissues
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27. Unit A : Chapter 1 : Section 1
What is a Base?
All of these products contain Bases
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What is a Base?
Like other bases, NaOH is an ionic compound
NaOH dissolves in H2O and breaks apart to form Na+ ions and OH- ions
NaOH is added to H2O
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What is a Base?
Strong bases will break apart completely to form lots of OH- ions, which are corrosive
NaOH is added to H2O
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30. Unit A : Chapter 1 : Section 1
What is a Base?
A base is any compound that increases the number of OH-, or hydroxide, ions when dissolved in water
Strong bases, like strong acids, are corrosive, meaning they can destroy clothing and body tissues
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31. Unit A : Chapter 1 : Section 1
What is a Salt?
All of these products contain a Salt
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32. Unit A : Chapter 1 : Section 1
What is a Salt?
When you hear the word salt, you probably think of table salt
But salts are any ionic compounds formed from the positive ion of a base and the negative ion of an acid
NaCl, or Salt Crystals
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33. Unit A : Chapter 1 : Section 1
What is a Salt?
The Na+ from the base and the Cl- from the acid bond to form NaCl, salt
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34. Unit A : Chapter 1 : Section 1
What is a Salt?
The H+ from the acid and the OH- from the base bond to form H2O, water
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35. Unit A : Chapter 1 : Section 1
What is a Salt?
A salt is an ionic compound formed from the positive ion of a base and the negative ion of an acid
Salts are used to season our foods, make soap, treat our pools, and settle our stomachs
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36. What is the difference between ionic compounds and covalent compounds?
Let’s Review!
- 1 -
What is the difference between ionic compounds and covalent compounds?
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37. How are they all related?
Let’s Review!
- 2 -
What is an acid?
What is a base?
What is a salt?
How are they all related?
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38. Unit A : Chapter 1 : Section 1
Chemical Compounds
Web Sites to Visit:
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39. Unit A : Chapter 1 : Section 1
Pre-AP Extensions
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