Take Home Lab #4

Take Home Lab #4:  Molecular Shape

Question: How does the shape of a molecule affect its chemical properties?

Safety: Clean up any spilled or splashed water when finished to avoid slipping.

Materials: Comb, balloon, or other source of static electricity; water faucet.

Procedure: Because oxygen has six valence electrons (Figure 1), it bonds with two hydrogen atoms, each having one valence electron. But there are two different configurations that this combination could make. The hydrogen atoms could line up across from each other (Figure 2), or they could arrange themselves next to each other (Figure 3).

                The way to tell which configuration the water molecule actually takes the form of is to test its properties. In the configuration in Figure 2, the hydrogen atoms are slightly positive because the oxygen atom is pulling on the electrons harder than the hydrogen atom. Therefore, each end of the molecule is positive (nonpolar covalent) and water would not be affected by its static electricity. In the configuration in Figure 3, the hydrogen atoms are both on the same side and two pairs of electrons (negative) are on the other side. This would make the water molecule have poles like a magnet (polar covalent), and it would be affected by static electricity.

1. Test whether a thin stream of water from a faucet is affect by static electricity or not.

2. Static electricity can be generated in many ways. Be sure that the object is charged by showing that hair is attracted to it.

                a. Rub a balloon on your hair or a pet’s hair.

                b. Comb your hair with a plastic comb.

3. Put the comb or the balloon next to (but not touching) a slow running water faucet and observe what occurs.

4. Use the comb or balloon to see if it will affect small pieces of paper, salt, pepper, small scraps of aluminum foil and sugar.  Record your observations.

Post-Lab Questions:

1. What happened, if anything, when you brought the static electricity near the stream of water?

2. Which figure (2 or 3) shows the actual structure of water?

3. Molecules that have a partial positive charge on one end and a partial negative charge on the other end are said to be polar. Molecules that have the same charge on both ends are called nonpolar. Is water polar or nonpolar?

4. Examine the electronegativities (from pg. 403 in textbook), do the values for hydrogen and oxygen support your answer for #3?

5. Fill in the data table for your results from #4 above.

Substance:	Attracted?:	Polar or nonpolar?:
Paper
Salt
Pepper
Aluminum Foil
Sugar