Answer:
Simple Daltons atomic theroy and Through chemical reactions we can witness their effects. Through mathematical equations combined with indirect observations, we can calculate their various sizes. And finally, with the aid of new technologies such as the Scanning Tunnelling Microscope, atoms can now be seen.
Step-by-step explanation:
The first accurate theory explaining the nature of matter was Dalton's Atomic Theory: 1. All matter is composed of atoms, and atoms are indivisible and indestructible. Elements are composed of identical atoms, but the atoms of each element are different and distinguishable from each other.(Look up Daltons atomic theroy)