Introduction to the Particle Theory of Matter

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Learn about how the Particle Theory helps us understand matter.

Particle Theory of Matter 

Matter is anything that has mass and takes up space. It is a general name given to all the things physically around us. Matter includes things so tiny you can’t see them with your eyes.

Part(icles) of Your World (2015) by Crash Course Kids (3:49 min.)


The Particle Theory of Matter is a scientific model. A scientific model is a way of illustrating ideas, objects and processes so they’re easier to understand. Scientists use models to explain things we can’t see without advanced equipment. One of these things is an individual atom.

The Particle Theory of Matter helps us think about how matter behaves. It also helps us explain why different matter has different properties. It has several key ideas:

  1. All matter is made of tiny particles. These particles are either individual atoms or groups of atoms called molecules.
Diagram of an oxygen atom and a water molecule
Left: Bohr atomic model of oxygen; Right: Bohr atomic model of water (Let’s Talk Science using an image by VectorMine via iStockphoto).

Did you know?
Any particle smaller than an atom is called a subatomic particle. Protons, neutrons and electrons are all subatomic particles.

  1. Atoms of the same element are the same. Atoms of different elements are different. All of the atoms in carbon are the same. But carbon atoms are different from the atoms in nitrogen and oxygen.
Atomic diagrams of carbon, nitrogen and oxygen
From left to right: Bohr atomic models of carbon, nitrogen and oxygen (Let’s Talk Science using an image by VectorMine via iStockphoto)
  1. Particles are attracted to each other. There are forces that attract particles to each other. In some kinds of matter, like a diamond, the force is very strong. In other kinds of matter, like juice in a glass, the force is weaker.
  1. Particles of matter have spaces between them. Atoms and molecules have spaces between them. In a gas, there are large spaces between them. In a a liquid they are closer together. In a solid, the particles are packed close enough together they can hardly move.
Atomic arrangement in a solid and in a liquid
Left to right: Atoms in a solid, like diamond; Atoms in a liquid, like juice and Atoms in a gas, like air (Let’s Talk Science using an image by VectorMine via iStockphoto).


  1. Particles are always moving. Particles of matter move constantly at any temperature above -273.15 degrees Celsius. But the human eye can’t see them move.

Did you know?
-273.15 degrees Celsius is also 0 kelvin (0 K). This temperature is called absolute zero.

  1. How fast particles move affects their temperature. The higher the speed of the particles, the higher their temperature. 
Diagram showing the movement of particles in three different temperatures
The faster the speed of particles, the higher the temperature (Let’s Talk Science using an image by VectorMine via iStockphoto).


Learn More

The Particle Theory of Matter Quiz

See how well you know the particle theory. Try this short quiz by Science Source.

What's Matter? 

This video (3:30 min) by Crash Course Kids explains three states of matter: Solid, Liquid, and Gas. There is also a quick experiment you can do at home to prove that air is matter.