Physical Science
Chapter 3: The Structure of Matter
Name:________________________
Chapter 3, Lesson 1: What Are Molecules?
Section Goal: The student will describe the size of molecules, explain what a molecule is, explain how
molecules move in each of the three states of matter and describe what plasma is.
Vocabulary:
1. Molecule2. Atom3. Solid4. Liquid5. Gas6. State of matter7. Plasma-
Lesson 1: NOTES
You may describe sugar by its properties (color, taste, texture), but how would you describe a single grain of sugar?
You might say it is very small. But how small is the smallest piece of sugar?
Size of Molecules
Each grain of sugar is made of even smaller particles that are too tiny for you to see. These tiny particles are called
molecules (the smallest particles of a substance that still have the properties of that substance.) Each molecule of sugar
has exactly the same properties.
How small can molecules be? They are so small that billions of them could be places side by side on a line one
centimeter long!
Describing Molecules
Imagine dividing up one drop of water into smaller and smaller drops. The smallest drop you could make that still have
the properties of water would be one molecule of water. In general, all water molecules are alike. Ex: A molecule of
water from the ocean, a raindrop and the water you drink.
In the figure of the molecule of water, you can see it has three parts – one large part and two smaller parts. If you divide
up the water molecule, it would no longer have the properties of water. Each individual part of the water molecule is
called an atom (the building block of mater.)
So each water molecule has three atoms. Each kind of atom has its own properties. All matter is made of atoms.
States of Matter
You can describe matter by telling about its properties (mass, density) but the form (solid, liquid, gas) that matter has is
another of its properties.
How many solids, liquids and gases can find in the picture below:
The trees and homes are solids. In solids, the molecules in a solid attract, or pull toward each other. In a solid, the
molecules vibrate, which means that they move back and forth quickly, but stay close together.
The water in the picture is a liquid. The pull between the molecules is weaker in liquids than it is in solids. They slide
past each other. A liquid has a certain volume but changes it shape because its molecules can easily move around. You
can take a bottle of water and pour it into different containers, but it will still be the same amount.
The helium balloon is filled with a gas. The molecules are much farther apart than they are in a liquid or a solid. The pull
between the molecules is very weak and will take the shape of its container, filling it completely. In our picture, it is the
shape of the balloon. The volume of a gas can change.
Plasma
Matter can also exist in a fourth state of matter called plasma (a very hot gas made of particles that have an electric
charge.) The particles of plasma shake violently at very high temperatures. Plasma is very rare on Earth. All stars,
including the sun, are balls of plasma.
Lesson Reflection:
Complete the Solids, Liquids and Gases handout.
Self-Check:
1. What is a natural element?
2. Give three examples of natural elements.
3. Table salt is made up of a sodium atom and two chlorine atoms. Is table salt an element? Explain.
Technology/Application/Connection to real-world: