Lesson 1.3: Matter combines to form different substances

Lesson Focus

Explore how matter is classified. We'll discover the difference between pure substances and mixtures, and see how atoms combine to build everything around us, from simple elements to complex compounds.

Learning Objectives

• Distinguish between pure substances, like elements and compounds, and the various types of mixtures.
• Understand the relationship between atoms and elements, where an element consists of only one type of atom.
• Learn how different atoms chemically bond together to create new substances known as compounds.

Scientists classify matter by its composition.

Pure matter contains only one type of component, like pure water having only water molecules.

Mixed matter, like air or lemonade, combines two or more different substances that are not chemically bonded.

A single type of atom builds a pure substance called an element.

Because all its atoms are identical, an element cannot be broken down into simpler materials. For example, a piece of pure aluminum contains only aluminum atoms.

Think of elements as the fundamental ingredients for all matter.

Different types of atoms chemically bond in a fixed ratio to form a compound.

This new substance has properties completely different from its original elements.

For example, water (H₂O) is a compound made from hydrogen and oxygen. The chemical bonds lock the atoms together, creating something entirely new.

Substances can combine physically to form a mixture.

Unlike in compounds, the individual substances in a mixture are not chemically bonded and keep their original properties.

Because they are only physically combined, they can often be separated by physical means. A fruit salad is a great example—you can still see the fruit!

Mixtures are classified by how evenly their parts are spread out.

A heterogeneous mixture, like soil, has visibly different components.

A homogeneous mixture, like salt dissolved in water, appears uniform throughout because the substances are evenly distributed.

Compounds and mixtures are not the same. In compounds, atoms are chemically bonded in a fixed proportion to form a new substance.

In mixtures, substances are physically combined in variable proportions and keep their original identities.

The key difference is the presence or absence of chemical bonds.