Lesson 1.2: Matter is made of atoms

Lesson Focus

Everything around us is made of incredibly tiny particles called atoms. We will explore these fundamental building blocks and see how they combine to form the matter we interact with every day.

Learning Objectives

• Identify atoms as the fundamental particles of matter and understand their incredibly small scale.
• Describe how atoms bond together to form molecules, creating different substances like water.
• Explain that atoms and molecules are always in constant motion in solids, liquids, and gases.
• Use a model to understand how scientists can determine the mass of a single, invisible atom.

All matter is made of atoms, the smallest basic units. Imagine breaking a rock into its tiniest possible pieces—you'd have atoms.

A desk isn't solid but is a collection of atoms with empty space between them. We can't see them, but they build our entire world.

Everything is atoms!

Since a single atom is too small to weigh, scientists measure its mass indirectly.

They find the mass of a huge collection of atoms and divide by the number of atoms to get an average.

This is like finding one penny's mass by weighing ten. This modeling reveals an individual atom’s mass.

Atoms bond together to create molecules.

A molecule, like water (H₂O), is the smallest particle of a substance that is still that substance.

If you break a water molecule apart into hydrogen and oxygen atoms, you no longer have water. Molecules are the building blocks of specific substances we know.

A substance's identity depends on its molecular recipe.

For example, an oxygen molecule (O₂) and an ozone molecule (O₃) are both made of oxygen atoms, but the different number of atoms makes them entirely different substances.

Changing the atoms in a molecule creates something new. What makes up carbon dioxide (CO₂)?

Atoms and molecules are always moving.

We see this when invisible air molecules push dust particles around in a sunbeam, causing them to dart about.

This constant motion also causes food coloring to spread through water. Even in solids, particles are constantly vibrating in place; they are never truly still.