Dalton's ideas about atoms

The idea

All matter is made of tiny atoms that take part in chemical reactions and are indivisible, never created or destroyed in them; atoms of an element are identical in mass and chemical properties, unlike those of other elements.

Are all atoms alike?

Dalton thought about the tiny particles that make up matter.

Which statement do you think matches Dalton's postulates?

• Atoms of one element are identical, but differ from atoms of another element
• Atoms of one element can all have different masses
• Atoms of hydrogen and oxygen are exactly alike

Four postulates

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Four ideas about atoms

Put the four postulates together: atoms are the building blocks, they stay whole in reactions, atoms of one element are alike, and atoms of different elements differ.

All matter is made of tiny atoms that take part in chemical reactions. Atoms are indivisible, and are never created or destroyed in a chemical reaction. Atoms of an element are identical in mass and chemical properties, unlike the atoms of other elements.

Notes

All matter is made of atoms. Atoms are indivisible and not created or destroyed in a reaction. Atoms of an element are identical; atoms of different elements differ.

Check yourself

What did Dalton say about atoms in a chemical reaction?

Two hydrogen atoms are compared. What do Dalton's postulates say?

A hydrogen atom and an oxygen atom are compared. What do Dalton's postulates say?

According to Dalton, what is all matter made up of?

• They are split into smaller parts. Dalton said atoms are indivisible, so they are not split.
• They cannot be created or destroyed — correct. Yes!
• They are changed into atoms of other elements. Atoms are not created or destroyed, and they do not turn into something else.
• They can have different masses. Atoms of a given element are identical in mass.
• They have different chemical properties. Atoms of a given element are identical in chemical properties.
• They are identical in mass and chemical properties — correct. Yes!
• They differ in mass and chemical properties — correct. Yes!
• They are identical in mass and chemical properties. Atoms of different elements have different masses and chemical properties.
• They have the same chemical properties but different masses. Atoms of different elements differ in both mass and chemical properties.
• A smooth substance with no parts. Dalton said matter is made up of tiny particles called atoms.
• Very tiny particles called atoms — correct. Yes!
• Particles that can be created in chemical reactions. Atoms cannot be created or destroyed in a chemical reaction.