October 2003

"Please pass the sodium chloride." That's just another way you can request the salt for your baked potato the next time you sit down with your family for dinner. Sodium chloride, regular table salt, is also known as the mineral halite. The diagram to the right shows how sodium and chlorine atoms pack tightly together to form cube-like units of the compound NaCl. Crystals of table salt imitate this structure-they're shaped like little cubes. You can check this out for yourself by viewing a few grains of salt through a magnifying lens or microscope.

A salt mine more than 1,000 feet
below Detroit

Where does table salt come from? (Please, don't say the supermarket.) Halite, sodium chloride, is found naturally in huge geologic deposits of salt minerals left over from the slow evaporation of ancient seawater. (Are you surprised? Ever get a taste of seawater in your mouth at the beach?) These deposits are mined for various salts, including enough sodium chloride to fill many, many salt shakers!

What's in a name?

NaCl is the chemical short-
hand (or formula) for sodium chloride. It's easy
to see where "Cl" comes from (chlorine, duh), but how is it, you may ask, that "Na" represents sodium?

The answer is that "Na"
stands for "natrium," the
Latin word for sodium.

NaCl is absolutely essential to life on earth. It is a necessary ingredient in the diets of people and animals. And sodium chloride has literally thousands of uses! One of those uses is to serve as a source of chlorine for chemical manufacturing. Why, you may ask? Here's why: chlorine is known as a "workhorse chemical." It plays a key role in the manufacture of thousands of products we depend on every day, including volleyballs, computers, cars, pool chemicals, medicines and cosmetics (check out the Chlorine Product Tree). Those are just a small sampling of the many items that are made using chlorine.

How do you think chlorine is freed from those tightly packed crystals of NaCl? Electricity is the tool used to electro-chemically split NaCl, releasing Cl for its many chemical uses. Chemical engineers design systems to make chlorine gas bubble out of salty, electrified water. The gas is captured and cooled down so much that it liquefies.

The whole process is very cool (but not safe for you to try at home). The average American consumes about 7 pounds of sodium chloride each year and more than 500 pounds over the course of a lifetime! Put that together with the use of all the products made using chlorine, and I think you will agree that NaCl is an essential compound!

Please pass the halite!

Follow-Up Questions:

  1. Find sodium and chlorine on The Periodic Table of the Elements. What are their atomic numbers? What information can we get from an element's atomic number?

  2. NaCl is known as an ionic compound. What does that mean?

  3. Chlorine is known as a diatomic molecule. Explain what that means. (Hint: "di" means "two.")

Science Project Ideas:

  1. Halophytes are plants that have adapted to life in high-salt environments. Name some of these environments and describe some of the halophytes found there. How have they adapted to a "salty" existence? What happens to ordinary plants when they are watered with salty water?

  2. Find out the chemical compound and mineral names for some of the other salts that form from the slow evaporation of ancient seawater (besides sodium chloride). What are they used for?

For a list of previous "Chlorine Compound of the Month" features, click here.


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