Particles like molecules are tiny bits of matter that make up gases.

Which gas makes up the biggest part of our air?

Nitrogen is the most common gas in the air, while oxygen makes up about one-fifth.

Why do you not feel air molecules hitting your face?

Air molecules bounce off you all day, but they are far too small and light to feel.

How is a gas different from a solid?

A solid like a rock keeps its shape, but a gas spreads out to fill empty space.

What sits between the molecules in a gas?

Gas molecules stay far apart from each other, leaving lots of empty space for light to travel through.

Tiny Bits in the Air

Why the Sky Changes Colors — illustrated by glass prism refracting sunlight into a gradient spectrum, Victorian botanical illustration style. — **Why the Sky Changes Colors**

Look around you right now. You might see walls. You might see toys. You might see trees. What sits between you and those things? It looks like empty space. It is not empty at all. Air fills this space.

What Is Air?

Air is real stuff. You cannot see it. You cannot grab it with your hands. But you can feel it.

Wave your hand in front of your face. Do you feel a breeze? That breeze is air. It pushes against your skin.

Air acts like a giant invisible ocean. We live at the very bottom. It surrounds us all the time.

Three Kinds of Stuff

All stuff takes three main forms. A rock is a solid. A solid keeps its shape.

Water is a liquid. A liquid flows and spills.

Air is a gas. A gas does not keep its shape. A gas spreads out. It fills a whole room.

Tiny Bits Called Molecules

Particles make up gases . Particles are tiny bits of matter. Molecules are a type of particle.

A molecule is a very small bit. It is far too small to see.

Imagine a giant bucket of sand. Stand far away. The sand looks like one smooth thing.

Look very close at the sand. You will see millions of tiny grains. Air works the exact same way.

Billions of tiny gas molecules make up the air. They float all around us.

The Gases Inside Air

Air is not just one thing. It is a mix of different gases.

Think of a mixed bag of candy. You have red candies. You have blue candies. You have green candies.

Air is a mix of different gas molecules . Scientists can test air. They find the hidden gases inside.

In the source’s own words · reading level Grade 15.9

Introductory students design and carry-out experimental procedures to determine the identity of three unknown gases from a list of eight possibilities: air, nitrogen, oxygen, argon, carbon dioxide, helium, methane, and hydrogen.

In plain terms: people can test invisible gases. They can figure out the gas names. They find a big mix in the air.

Let us list the main gases in our air:

Nitrogen: This gas is the biggest part.
Oxygen: This is the gas our bodies need.
Argon: This is a very small part.
Carbon Dioxide: Plants need this gas to grow.

The Need for Oxygen

Nitrogen gas makes up most of the air. It makes up more than half.

The next biggest part is oxygen. We need oxygen to live. You take a breath. You pull oxygen into your body.

In the source’s own words · reading level Grade 9.6

Oxygen is one of the component gases of air at room temperature, making up around 20% of the atmosphere.

In plain terms: oxygen is a gas. It makes up one-fifth of our air.

A man named Joseph Priestley studied air . He helped discover oxygen. He learned this gas is very special.

How the Molecules Move

These tiny gas molecules never sit still. They zoom around very fast. They bounce off each other.

They bounce off you, too. Think of bumper cars at a fair. The cars zip around. They crash into things.

Air molecules do this all day long. They act like tiny bouncy balls. They fly through the air.

They hit a wall and bounce off. They hit your desk and bounce off. Millions hit your face every second.

You do not feel them. They are too small. They are too light.

Here is a chart of our air:

Empty Space

Let us think about the space between the molecules. Molecules pack tightly together inside a rock. They do not move much.

Things act differently in a gas. The molecules stay far apart. Empty space sits between them.

Think of a huge soccer field. Imagine ten kids on the field. The kids run around.

The kids stay very far apart. They have lots of room to run. Air molecules act like those kids.

They have lots of empty space around them. This empty space is very important. Light needs space to travel.

Getting Ready for Light

Sunlight colors travel from the sun. We learned about white light. We learned about light waves.

The light waves zoom through space. They reach our planet. The light waves fly through the empty space.

But sometimes a light wave hits a molecule. The light wave crashes into the gas molecule. It acts like a bowling ball hitting a pin.

Different sunlight colors have different sizes. We measure them from crest to crest. Red light waves are long. Blue light waves are short.

The size of the wave changes things. This size changes the crash.

We will see this happen very soon. The crash makes the sky change colors. Next, we will watch the light hit the air.

Key Terms

Molecule — A very small bit of stuff that makes up gases, liquids, and solids.
Gas — A type of stuff that does not keep its shape and spreads out to fill a room.
Oxygen — A gas in the air that our bodies need to live.
Nitrogen — The gas that makes up the biggest part of the air around us.