## Lesson Introduction

When you scramble an egg or try to get rid of the rust spots on your car, you are using the principles of chemistry. Chemistry is the study of the composition and properties of matter. Matter takes up space and has mass. Matter can exist as a solid, a liquid, or a gas. Iron, orange juice, and air are all matter. They take up space and have mass.

All matter has physical properties that our senses can detect. These include:

• Color. By looking, you see that a baseball is white and a tennis ball is yellow. Some matter is colorless.
• Odor. By smelling, you can tell whether someone is wearing perfume or not. Some matter has no odor, however.
• Taste. By tasting, you can tell the difference between a cola drink and ginger ale. But some matter is tasteless.
• Hardness. By touching, you can tell how hard matter is. It may be as hard as a diamond or as soft as a pillow.

Mass is the amount of matter a substance has. Anything that has mass can be weighed. Weight is a measure of the pull of gravity on an object. An object’s weight depends on where you weigh it. For example, say you have a barbell that weighs 100 pounds on Earth. If you took that barbell to the moon, it would weigh only 17 pounds. That’s because the pull of gravity on the moon is weaker than the pull of gravity on Earth.

Another important physical property of matter is density. Density is the amount of mass in a specific volume of matter. The more mass per unit of volume, the denser an object is. For example, one cubic foot of solid steel is denser than one cubic foot of plastic foam. The steel has more mass, even though it occupies the same amount of space as the plastic foam.

This lesson introduces some of the basic ideas in chemistry, beginning with the properties and states of matter.