Well, for starters, you are matter.  Your hair is matter, your eyes and legs are matter, and the shoes you are (probably) wearing are matter.  So too are stars, sailboats, and sand. You may recall learning that matter is “anything that has mass and takes up space”.

The definition of matter is important in chemistry because chemistry can be defined as the study of matter and the types of changes that it undergoes, including the energy changes associated with those changes.

In middle school chemistry, we playfully refer to matter as “stuff”.  Using that definition, chemistry is the “stuff that stuff does”.

As you know, most matter fits neatly into one of three main categories: solid, liquid, or gas.

Because we encounter them every day, it’s pretty easy for us to confirm that solids are matter.  Consider your desk, for example.  It takes up space and has mass.  It’s matter.  How about liquids?  Consider a glass of water or your favorite soda.  They take up space and have mass, so they’re matter, too.

But what about gas?  Are gases matter?  Although we’re surrounded by them at all times, it’s more difficult for us to interact with gases because they are so diffuse.  If we use containers that hold gases, however, like basketballs or balloons, we can see more easily that gases have mass and take up space.  Gases are therefore also matter.

Can you think of some examples of things that are not matter?  One good example of something that is not matter is energy.  In fact, providing a brief and simple definition of energy is somewhat tricky to do, but we can think of energy as the ability to do work or cause change.  Energy isn’t matter, then, because it isn’t stuff — it does not take up space and we can’t weigh it, so it doesn’t have any mass.

In our daily lives, we often experience energy in the form of heat.  And perhaps if you’ve completed Chapter 6 of Middle School Chemistry, you know that some chemical reactions absorb or release energy in the form of heat.

Interestingly, one the pioneers of modern chemistry, Antoine Lavoisier, developed a now obsolete scientific theory that proposed that energy was matter.  Lavoisier thought energy was a fluid called “caloric” that flowed from warmer bodies to colder bodies.  It wasn’t until many years later that challenges to Lavoisier’s caloric theory arose.

One challenge came from Count Rumford, who in 1798 showed that boring out cannons, which is the process of drilling holes in cannon barrels, produced heat from friction over very long periods of time.  Rumford used an apparatus in which a blunt cannon bore had one end submerged in water.  As the blunt bore was rotated against the cannon barrel, the friction generated heat, and caused the water the bore was submerged in to boil.  Conducting this experiment over long periods of time, Rumford concluded that he could produce heat in this way indefinitely.  This caused him to question Lavoisier’s theory, because Rumford felt that because he could generate heat indefinitely, heat must not be a substance.

We should be careful to note that although Lavoisier was incorrect in this instance, he was an otherwise exceptional chemist, and is often called the “father of modern chemistry”.  In fact, because he was so respected, his now discredited caloric theory continued to be used for many years, and prevented many of his peers from questioning him.

Although we know today that energy is not matter, the path to our modern understanding of science has been paved by prominent chemists who questioned what we view today as fundamental concepts of matter.