1. The Building Blocks of Matter
- Elements and Atoms
The Building Blocks of Matter
Matter may consist of elements, compounds, or mixtures.

2. Ions and Ionic Bonds - Ionic Bonds
You and a friend walk past a market that sells apples for 40 cents each and pears for 50 cents each. You have 45 cents and want an apple. Your friend also has 45 cents but wants a pear.

3. Ions and Ionic Bonds - Ionic Bonds
When an atom loses an electron, it loses a negative charge and become a positive ion. When an atom gains an electron, it gains a negative charge and becomes a negative ion.

4. Ions and Ionic Bonds - Ionic Bonds
Ions are atoms that have lost or gained electrons.

5. Ions and Ionic Bonds - Ionic Bonds
Ionic bonds form as a result of the attraction between positive and negative ions.

6. Properties of Ionic Compounds
- Ionic Bonds
Properties of Ionic Compounds
In general, ionic compounds are hard, brittle crystals that have high melting points. When dissolved in water or melted, they conduct electricity.

7. Formation of an Ionic Bond
- Ionic Bonds
Previewing Visuals
Before you read, preview Figure 17. Then write two questions that you have about the diagram in a graphic organizer like the one below. As you read, answer your questions.
Formation of an Ionic Bond
Q. What is an ionic bond?
A. An ionic bond is the attraction between two oppositely charged ions.
Q. What is the overall charge on an ionic compound?
A. Overall, an ionic compound is electrically neutral.

8. Click the Video button to watch a movie about salt.
- Ionic Bonds
Salt
Click the Video button to watch a movie about salt.

9. Links on Ionic Compounds
- Ionic Bonds
Links on Ionic Compounds
Click the SciLinks button for links on ionic compounds.

10. End of Section: Ionic Bonds

11. How Covalent Bonds Form
The force that holds atoms together in a covalent bond is the attraction of each atom’s nucleus for the shared pair of electrons.

12. How Covalent Bonds Form
The oxygen atom in water and the nitrogen atom in ammonia are each surrounded by eight electrons as a result of sharing electrons with hydrogen atoms.

13. How Covalent Bonds Form
An oxygen molecule contains one double bond, while a carbon dioxide molecule has two double bonds. A nitrogen molecule contains one triple bond.

14. Comparing Molecular and Ionic Compounds
- Covalent Bonds
Comparing Molecular and Ionic Compounds
The table compares the melting points and boiling points of a few molecular compounds and ionic compounds. Use the table to answer the following questions.

15. Comparing Molecular and Ionic Compounds
- Covalent Bonds
Comparing Molecular and Ionic Compounds
Graphing:
Create a bar graph of just the melting points of these compounds. Arrange the bars in order of increasing melting point. The y-axis should start at –200ºC and go to 900ºC.
Check that the graphs are correctly set up and labeled before students plot the data.

16. Comparing Molecular and Ionic Compounds
- Covalent Bonds
Comparing Molecular and Ionic Compounds
Interpreting Data:
Describe what your graph reveals about the melting points of molecular compounds compared to those of ionic compounds.
Melting points of molecular compounds are lower than those of ionic compounds.

17. Comparing Molecular and Ionic Compounds
- Covalent Bonds
Comparing Molecular and Ionic Compounds
Inferring:
How can you account for the differences in melting points between molecular compounds and ionic compounds?
Molecular compounds have weak attractive force between molecules, so less energy is needed to melt molecular compounds.

18. Comparing Molecular and Ionic Compounds
- Covalent Bonds
Comparing Molecular and Ionic Compounds
Interpreting Data:
How do the boiling points of the molecular and ionic compounds compare?
Boiling points of molecular compounds are lower than those of ionic compounds.

19. Comparing Molecular and Ionic Compounds
- Covalent Bonds
Comparing Molecular and Ionic Compounds
Predicting:
Ammonia’s melting point is –78ºC and its boiling point is –34ºC. Is ammonia a molecular compound or an ionic compound? Explain.
Students may predict that ammonia is a molecular compound because it has relatively low melting and boiling points.

20. Unequal Sharing of Electrons
- Covalent Bonds
Unequal Sharing of Electrons
Fluorine forms a nonpolar bond with another fluorine atom. In hydrogen fluoride, fluorine attracts electrons more strongly than hydrogen does, so the bond formed is polar.

21. Unequal Sharing of Electrons
- Covalent Bonds
Unequal Sharing of Electrons
A carbon dioxide molecule is a nonpolar molecule because of its straight-line shape. In contrast, a water molecule is a polar molecule because of its bent shape.

22. Asking Questions - Covalent Bonds
Before you read, preview the red headings. In a graphic organizer like the one below, ask a what or how question for each heading. As you read, write answers to your questions.
Question
Answer
How do covalent bonds form?
Covalent bonds form when two atoms share electrons.
What are molecular compounds?
Molecular compounds are compounds that contain molecules bonded with covalent bonds.
How does unequal sharing of electrons affect the atoms in molecular compounds?
Unequal sharing of electrons causes the bonded atoms to have slight electrical charges.

23. Links on Molecular Compounds
- Covalent Bonds
Links on Molecular Compounds
Click the SciLinks button for links on molecular compounds.

24. End of Section: Covalent Bonds

25. Metallic Bonding - Bonding in Metals
A metal crystal consists of positively charged metal ions embedded in a “sea” of valence electrons.

26. Metallic Properties - Bonding in Metals
The “sea of electrons” model of solid metals explains their ability to conduct heat and electricity, the ease with which they can be made to change shape, and their luster.

27. Relating Cause and Effect
- Bonding in Metals
Relating Cause and Effect
As you read, identify the properties of metals that result from metallic bonding. Write the information in a graphic organizer like the one below.
Effects
Electrical conductivity
Heat conductivity
Cause
Metallic bonding
Ductility
Malleability
Luster

28. Links on Metallic Bonding
- Bonding in Metals
Links on Metallic Bonding
Click the SciLinks button for links on metallic bonding.

29. End of Section: Bonding in Metals

30. Graphic Organizer Polar Covalent Bond Nonpolar Covalent Bond
Metallic Bond
Feature
Ionic Bond
Attraction between oppositely charged ions
Attraction between positive ions and surrounding electrons.
How Bond Forms
Unequal sharing of electrons
Equal sharing of electrons
Charge on Bonded Atoms?
Yes, slightly positive or slightly negative
Yes; positive or negative No
Yes; positive
H2O molecule (or other polar covalent molecule)
NaCl crystal (or other ionic compound)
Example
Calcium (or other metal)
O2 molecule

31. End of Section: Graphic Organizer