Grade 5
The Human Knowledge Project
Unit 11 — Matter, Atoms, Molecules, and Chemical Changes
Welcome back!
Everything around us is made of matter.
The air we breathe, the water we drink, the food we eat, and even our own bodies are made of tiny particles.
Today you will learn how scientists describe matter and how it can change.
Reviewing Matter
Matter is anything that:
- has mass
- takes up space
Everything you can touch is made of matter.
Even many things you cannot easily see, such as air, are forms of matter.
Atoms
Scientists have discovered that all matter is made of extremely small particles called atoms.
Atoms are so small that millions could fit across the width of a human hair.
Different kinds of atoms combine to make every substance in the universe.
Elements
An element is a pure substance made from only one kind of atom.
Examples include:
- hydrogen
- oxygen
- carbon
- iron
- gold
- helium
Scientists have identified more than one hundred different elements.
Each element has its own unique properties.
Molecules
Atoms often join together to form molecules.
For example:
A water molecule contains:
- two hydrogen atoms
- one oxygen atom
Different combinations of atoms create different substances.
Mixtures
Sometimes substances combine without forming a new substance.
These combinations are called mixtures.
Examples include:
- trail mix
- salad
- air
- salt water
The parts of a mixture can often be separated.
Physical Changes
A physical change affects the appearance or state of matter without changing what it is.
Examples include:
- melting ice
- freezing water
- breaking glass
- cutting paper
- dissolving sugar in water
The original substance remains the same.
Chemical Changes
A chemical change creates one or more new substances.
Examples include:
- burning wood
- baking bread
- rusting iron
- cooking an egg
Signs of a chemical change may include:
- color change
- heat or light produced
- gas released
- formation of a new solid
Conservation of Matter
During physical and chemical changes, matter is not destroyed.
Instead, it changes form or is rearranged.
Scientists describe this idea as the conservation of matter.
This principle helps scientists understand reactions and explain how materials change.
Activity
Observe several examples of matter.
For each example:
- identify whether it is an element, compound, or mixture (if known)
- describe its physical properties
- decide whether a demonstrated change is physical or chemical
- explain your reasoning
Record your observations in a science journal.
Practice
Answer these questions.
What is matter?
What is an atom?
What is an element?
How is a molecule different from an atom?
What is the difference between a physical change and a chemical change?
What does the conservation of matter mean?
Review
Today you learned:
- all matter is made of atoms
- elements contain one kind of atom
- molecules form when atoms join together
- mixtures combine substances without creating new ones
- physical changes do not create new substances
- chemical changes produce new substances
- matter is conserved during changes
Understanding matter helps scientists explain the physical world and the changes we observe every day.
Looking Ahead
Next we will investigate forces, motion, and energy, discovering how objects move, interact, and transfer energy throughout the universe.