Introduction
Chlorine, an Element That's Everywhere
Chlorine and Public Health
From Whiter Whites to Leukemia Medications
Introducing Building Block Chemistry
More Building Block Chemistry

Introduction

What do tents, jogging shoes, cosmetics and schoolbooks have in common? That's a good question to ask your science students. Looking for the answer will lead to an eye-opening lesson in building block chemistry.

Ask a class of middle-schoolers to open their textbooks to the periodic table and two lightning-fast reactions are likely to occur: eyes glaze over and brains change channels. Why? Because at first sight, all those chemical symbols and little blocks send one message, "Huhhh?"

In reality, those blocks represent more that 100 pure elements that combine to build just about every-thing in the world. That's a pretty awesome idea, even if your hero is Bart Simpson.

Even more incredible is the fact that just a handful of those elements make up over 99 percent of the Earth's crust, atmosphere, and oceans by weight. Oxygen, chlorine, silicon, aluminum, iron, phosphorous, calcium, sodium, potassium, magnesium, hydrogen, and carbon are true building blocks. They combine readily with other elements to form compounds. These "building block" elements can be likened to the foundation of a building: The reactions they spark are the basis of countless chemical formations.

Recognizing these elements as building blocks is essential to the study of science. And looking closer at one element in particular—one of the liveliest on the periodic table—can help ignite students' interest in building block chemistry. 

« back to top

Chlorine, an Element That's Everywhere

Of all the elements, chlorine is among the most active. It is almost never found free, or uncombined, because chlorine teams up with nearly every element it meets—in nature, in the research lab, or at a manufacturing plant.

That's why chlorine is often found in some surprising places and products. Chlorine makes up two percent by weight of all sea water on Earth. Chlorine is in our bodies and in our blood; it forms the hydrochloric acid that helps our stomachs digest food. While most people are aware of chlorine's use in swimming pools, in laundry bleach, or as a drinking water disinfectant—they may never guess that chlorine is used to make tents, jogging shoes, telephones, cosmetics, or schoolbooks.

Chlorine compounds are used in the production of thousands of consumer goods, pharmaceuticals, and industrial products. The process can be very complex, such as the use of chlorine compounds in making polyester or polyvinyl chloride (PVC) products, such as vinyl rain gear and house siding. Or it can be extremely simple. Combining sodium with chlorine yields sodium chloride, a product that's part of many meals—table salt.

Without chlorine compounds, we wouldn't have many of the products and services that we often take for granted. Skeptics need only look around the classroom—notebook paper, electronic gadgets, pencil erasers, cassette tapes—to grasp the real-life impact of chlorine and other building block chemicals.

« back to top

Chlorine and Public Health

Because water is so basic to our existence, ensuring safe drinking water also would be a natural topic for student exploration and class discussion. For example, the Latin American cholera epidemic in the news over the past year is a shocking reminder of what can happen when drinking water is not adequately disinfected. In fact, it is estimated that more than 25,000 children worldwide die every day from causes related to dirty water.

At the same time, questions have been raised about potential risks from drinking water that has been disinfected. While disinfection eradicates such life-threatening diseases as cholera, typhoid, and dysentery, some studies suggest it also may slightly increase the risk of certain types of cancer. The scientific and public health communities recognize that the benefits of disinfected drinking water outweigh the potential risk. But why not find out for yourself? Explore these issues with your students. As a class, weigh the risks and benefits of water disinfection.

Talk with your local public health officials to learn more about the threat of waterborne diseases and the use of chemicals (including chlorine) for water disinfection. Contact your local water-treatment authorities to arrange a visit to a local water plant for a close-up view of how water is made safe to drink. Conduct library research to learn more about waterborne diseases on a global scale. Perhaps most educational, facilitate class discussion on what students have learned, including how society uses science to weigh risks and benefits in areas such as public health.

« back to top

From Whiter Whites to Leukemia Medications

Chlorine, the seventeenth atomic element, was discovered in 1774 by the Swedish chemist Carl Wilhelm Scheele. His find heralded the way for whiter whites. The bleaching properties of this new gas were an instant improvement over the only other method of lightening fabrics: bleaching them in the Sun for six weeks. However, there was one drawback. Chlorine gas rusted the metal machinery and equipment of the day, so it was not widely used. But in 1789, chlorine was combined with a potash solution that made it easier to use.

Interest in chlorine grew rapidly. Antoine Lavoisier, James Watt, Michael Faraday, and Humphry Davy (who first proved chlorine was an element) all experimented with chlorine. But it wasn't until early this century that chlorine's public health and commercial benefits became evident. Chlorine was found to be an effective drinking water disinfectant, virtually eliminating the threat of waterborne disease. About the same time, the discovery of an economical way to cool and pressurize chlorine gas paved the way for widespread commercial applications.

Today, chlorine is produced by electrolysis. An electrical current passed through salt water (from the sea or underground salt deposits) splits positive sodium and negative chloride ions. Since opposite charges attract, the negative chlorine ions collect at the positive poles to form molecular chlorine gas. The gas is dried, chilled, and pressurized or converted to liquid for storage and shipping. Chlorine is used as a building block in a range of products from laundry bleach to ski boots to leukemia medications.

Tune in students' imaginations to building block chemistry and hear some natural reactions—the "ahhs" and "ohhs" of discovery.

« back to top

Introducing Building Block Chemistry

Chlorine and chlorine compounds are a good way to introduce your students to building block chemistry without tackling the whole periodic table at once.

On its own, chlorine has a distinct odor, although smelling chlorine is not recommended. Liquid chlorine is amber in color. And in low concentrations, chlorine gas is nearly invisible. But when chlorine combines with other elements it does things that will keep students tuned in. Chlorine compounds can turn blue, brown, or sparkling white. They can change odor or have none at all. They can be hot or cold. They can bubble, liquefy, or harden. The ever-changing physical properties of chlorine compounds and the activities on the attached poster can help you deliver a two-day lesson on "What's in this stuff?"

Start by awing your students with magic: Turn "wine" (water tinted with red food coloring) into water right before their eyes. Household bleach, or sodium hypochlorite, is the secret ingredient that clears up the water. Once the secret is out, point to the poster to launch a hunt for all the unexpected things chlorine compounds help build. On day two, give students an opportunity to put chlorine to the test themselves—experimenting with a variety of chlorine salts—to see what happens when chlorine combines with other compounds. For instance, when light blue chunks of copper chloride react with ammonia, they turn dark blue. However, copper chloride's reaction with water and aluminum is surprisingly different; the new mixture bubbles, gets warm, and turns brown. A video that complements the lesson plan is also available free from the Chlorine Chemistry Division of the American Chemistry Council.

The accompanying activities were developed and tested by science teachers, with support from the Chlorine Institute, to supplement regular classroom chemistry studies. The objective of the lesson plan is to help students understand that chlorine is just one of several important single elements or building blocks essential to the production of a variety of different compounds.

The lesson procedures and guide-lines are complete, easy-to-use resources and tools for teachers. They can be implemented as they are or adapted to meet your needs. Lesson objectives, teaching strategies, and key discussion points are provided. The materials used in the experiments can be obtained inexpensively through any school science supplies vendor. Always follow your schools' safety precautions regarding chemical use, including providing protective eyewear for students.

« back to top

More Building Block Chemistry

To order a free copy of the Building Blocks of Our World: Chlorine video or additional activities that illustrate the use of chemicals in everyday life, please visit our  free resources section.

Other Activity Resources
Science Education for Public Understanding Program (SEPUP)
Lawrence Hall of Science
University of California
Berkeley, CA 94720
(510) 642-8718

The American Chemical Society
Education Division
1155 Sixteenth Street, NW
Washington, DC 20036

« back to top
News

News & Resources

View our resource center to find press releases, testimonies, infographics and more.

Jobs
LCSA