The stuff made of little particles. That particles had diferent forms.
The substances were created by diferent atoms, always in the same proportions.
That atoms can't be created and not destroyed.
He discobered the Electron. His model of atom was the "Chocolate chip cookie", a uniform atom with "chips" with positive and negative charge.
Discovered that the athom wasn't a full uniform part,in fact , it has a nucleus (positive and neutral charge) and around (negative charhe).
The negative charge (electron) go round the nucleus. They are able to change the orbit.
He made a new model of atom, but he didn't know were the atoms were located. So he put the in a "electronic cloud"