Episode 7: It’s in the Water

Activity Two: Understanding the Water Molecule

In this exercise, you will construct water molecules out of everyday household items and perform a series of demonstrations designed to get you to think about the molecular arrangement of water molecules in its three states and in seawater.

II. What You Will Need

1. 20-30 colored beads (at least four colors and sizes), or raisins, grapes, cranberries, and marshmallows (or similar food in four colors), or four different sizes of Styrofoam balls

2. Wire or toothpicks

3. Three petri dishes, or jar lids, or flat plates (bowls won’t work well)

III. Playing with water molecules

1. Pick one colored bead (or alternate object you chose) to represent the oxygen atom and one colored bead to represent the hydrogen atom. Find a picture of the water molecule in your textbook (or online) and construct a water molecule. Your water molecule must accurately represent the number of hydrogen and oxygen atoms and it must accurately represent the proper bond angle. (You will eventually need from 4-12 molecules to complete this activity so if you want to prepare them now, you may.)

2. Take a few moments and observe your water molecule. What do you see? Write your observations in the space below.

3. Draw a diagram of your water molecule below and indicate the following.

1.  hydrogen atom and its charge

2.  oxygen atom and its charge

3.  covalent bond

4.  bond angle

4. Now take another water molecule and arrange it so that it bonds with the first. Diagram your two bound water molecules below, indicating the charge separation on the molecule and the hydrogen bonds.

5. Arrange several water molecules together and note the possibilities for hydrogen bonding. Don’t forget to think in three dimensions when playing with your models. Illustrate the arrangement of several water molecules in two dimensions.

6. Water also occurs in three different states. Let’s identify places where you might find water as a gas, liquid or solid. Provide at least three locations for each state of matter. For example, the ocean is an example of liquid water.

Gaseous Water / Liquid Water / Solid Water
1. / 1. / 1.
2. / 2. / 2.
3. / 3. / 3.

7. Now, let’s think about the arrangement of water molecules as a gas, liquid or solid. Using dots or circles to indicate individual molecules of water, illustrate the spacing between water molecules as a gas, liquid or solid in each circle below.

8. Compare your illustration above to the ones found at http://www.ucar.edu/learn/1_1_2_3t.htm or Did you make the mistake of arranging the water molecules to be the closest in ice? Why are the spaces between water molecules in ice, greater than the spaces between water molecules in liquid water? Explain.

9. Illustrate below the arrangement of water molecules in ice. Explain the importance of the structure of ice to life on our planet.

10. Water has also been called the Universal Solvent, meaning it dissolves just about everything. Let’s use your models to illustrate how water dissolves and arranges itself around the major constituents of seawater. Pick a different bead (or alternate object) to represent sodium, Na+, a cation and another one to represent chloride (Cl-), an anion. Demonstrate the arrangement of water molecules around the sodium ion using your model. Do the same for the chloride ion. Check your textbook to verify that you’ve done it right. Then draw a diagram depicting the arrangement of water molecules around sodium and chloride. Label the following:

·  hydrogen atom and its charge

·  oxygen atom and its charge

·  sodium (or chloride) ion and its charge

·  ionic bonds

Water dissolving Na+

Water dissolving Cl-

IV. Discussion Questions

Answer the following below or on a separate sheet of paper.

1. How do models help us visualize and better understand molecular processes? In what ways are models limited?

2. Explain covalent, hydrogen, and ionic bonds. What are the relative strengths of each type of bond? Where do they occur in seawater?

3. What is the difference between the arrangement of water molecules around a cation and anion? How does the type of ion, cation, or anion affect the structure of water surrounding it?

Helpful Web Sites:

AquaDyn Technologies: The Water Molecule and Its Properties

http://www.aquadyntech.com/watermolecule.html

Water Structure and Behavior by Martin Chaplin

http://www.sbu.ac.uk/water/index.html

Iowa Project Wet

http://www.uni.edu/~iowawet/H2OProperties.html

University Corporation for Atmospheric Research

http://www.ucar.edu/learn/1_1_2_3t.htm