1. Are indivisible and indestructible particles. He believed that atoms could not be broken down into smaller parts.

2. Are the smallest unit of an element. This means that all atoms of a particular element are identical in size, mass, and chemical properties.

3. Combine in whole number ratios to form compounds. This explains why chemical reactions always involve specific, fixed ratios of elements.

4. Are rearranged in chemical reactions. He understood that atoms themselves aren't created or destroyed during a reaction, but they change their arrangement to form new substances.

It's important to note that some aspects of Dalton's theory have been modified over time with advancements in science:

* We now know that atoms are divisible into subatomic particles like protons, neutrons, and electrons.

* Atoms of the same element can have different masses (isotopes).

However, Dalton's Atomic Theory was a groundbreaking contribution to our understanding of matter, and many of its core principles remain valid today.