Lesson 2: Water and Its Characteristics

Wrapping Up

Conclusion

Today you learned about a second characteristic of water (polarity). Polarity is a characteristic that affects its behavior (consider the full glass activity). You also learned about two other concepts — cohesion and surface tension.

If you have the answers to the questions from the reading, begin to make a connection by using the information to consider the following scenario and possible solutions.

You are an ocean scientist (oceanographer) who has discovered a major problem. Water molecules that freeze and form ice no longer float. They are sinking. As a result, the world's oceans are beginning to freeze all the way from the surface to the bottom. As you investigate, you discover that the polarity of water molecules has been changed and water molecules are no longer polar. You have been approached by world leaders and respected oceanographers: What would you do? Explain why.

Here is a possible answer to the scenario your child has been asked to consider:

Understanding that the lack of polarity means that water no longer has a positive and negative pole, you begin to investigate what caused this. While you do not have an immediate answer, you recognize that the first step is to determine what substance has made the water stop being a polar molecule. The next step is to begin experimenting with ways to make water polar again. Your first option is to determine what has bonded with water and find a way to remove it so that water can become polar again.

Questions to Discuss

What do you call the attraction between polar molecules? (Cohesion).
Why is it important that cohesion exists between water molecules? (Cohesion between water molecules, as a result of covalent bonds, prevents water from evaporating quickly. As a result, climates remain moist and do not dry out as quickly).
If there were no cohesion between water molecules, how do you think this would affect the amount of clouds? (The ground would generally be drier, and with a greater amount of water in the sky, one could expect more clouds. The reduced cohesion of water molecules, however, may also mean that there are few clouds since the water molecules in clouds could not weakly bond together.)
If there were no cohesion between water molecules, how do you think this would affect the waters in the ocean? (There would be larger volumes of water that evaporate into the atmosphere because of reduced surface tension and cohesion. While the amounts would depend on other variables [temperature, atmospheric pressure], the lack of cohesion would lead to quicker evaporation [think about alcohol and how quickly it evaporates].)
How is cohesion beneficial in the behavior of water? (Cohesion prevents water from evaporating quickly. If there was less cohesion, water would evaporate more quickly likely leading to larger amounts of cloud cover because of increased amounts of water in the atmosphere).

Things to Review

Water is a polar molecule. It has a positive and a negative pole. The polarity of water causes cohesion between water molecules; this cohesion also results in surface tension. Surface tension is the evidence of polarity in water molecules.

Water is made up of hydrogen and oxygen atoms.

Remember that what is dissolved in water can influence the cohesion of water.

Making Connections: Discuss with your child how the characteristics of water are beneficial for the oceans and the climate.