From a guess to a theory

The idea

Dalton's atomic theory, the first scientific description of how matter is made, proposed that all matter is composed of indivisible particles called atoms, the fundamental building blocks of matter.

Break it again and again

Break a piece of chalk in two. Break each piece again, and again, in your mind.

More than 2,000 years ago thinkers imagined where this stops. In 1808 John Dalton gave a theory about it. What did Dalton say matter is made of?

• Indivisible particles called atoms
• A smooth stuff that has no parts
• Pieces that can always be split into smaller pieces

Three thinkers, one idea

Press Next step to walk through the history.

The first scientific description

The old ideas were imagined, not tested in experiments. Dalton built his theory on experiments of his time, so it was the first scientific description of how matter is made.

Dalton's atomic theory (1808), the first scientific description of how matter is made, proposed that all matter is composed of indivisible particles called atoms, the fundamental building blocks of matter.

Notes

Dalton's atomic theory (1808): all matter is made of indivisible atoms, the building blocks of matter. It was the first scientific description of how matter is made.

Check yourself

What made Dalton's atomic theory special?

In which year did Dalton propose his atomic theory?

In Dalton's theory, atoms are the fundamental building blocks of matter. What else did he say about them?

What does the Greek word atomos mean?

• It was the first time anyone had imagined tiny particles. Acharya Kanada and the Greek thinkers had imagined indivisible particles more than 2,000 years earlier.
• It was the first scientific description of how matter is made — correct. Yes!
• It said that atoms can be broken into smaller parts. Dalton proposed that atoms are indivisible, so they cannot be broken into smaller parts.
• 1897. In 1897 J. J. Thomson studied cathode rays, long after Dalton's theory.
• 1911. In 1911 Geiger and Marsden did the gold foil experiment, long after Dalton's theory.
• 1808 — correct. Yes!
• They are indivisible — correct. Yes!
• They are big enough to see with the naked eye. Atoms are so tiny that they cannot be seen with the naked eye.
• They can be split into smaller parts. Dalton said atoms cannot be broken down into smaller parts.
• Very heavy. Atomos means indivisible. Weight was not part of the word.
• Indivisible — correct. Yes!
• Electrically charged. Atomos means indivisible. Charge was not part of the word.