Democritus was a Greek philosopher who first thought everything was made of atoms

Thought it was earth wind fire and water.

The alchemists persisted

Boyle, Charles, and Lavoisier brought experiment back to chemistry

Used experiment and known data

Based upon experiment, not just thought as Democritus did

All matter is made of atoms
Atoms of the same element are identical
Atoms are never created destroyed or subdivided
Atoms combine in simple whole number ratios
Atoms combine separate or rearrange

Used magnetic and electric fields to discover that the cathode rays are both made of mass and are negative

Most alpha particles went through meaning the atom was mostly empty space
Some alpha particles were deflected meaning there was a positive charge in the atom
A few reflected meaning that there was a massive nucleus at the center of the atom

Th nucleus is like a dime in the center of Yankee Stadium. The stadium is empty space with a tiny nucleus

Used spectroscopy to predict the energy levels