DemocritusHe developed the concept of the atom means invisible.
John DaltonWhat: Proposed his modern theory of the atom. How: He based it upon :
1. Matter is made up of atoms that are indivisible and indestructible.
2. All atoms of an element are identical.
3. Atoms of different elements have different weights and different chemical properties.
4. Atoms of different elements combine in simple whole numbers to form compounds.
5. Atoms cannot be created or destroyed. When a compound decomposes, the atoms are recovered unchanged.
JJ ThomsonHe discovered the Plum Pudding Model of the atom.
Ernest Rutherfoldhe discovered that theorized that atoms have their positive charge concentrated in a very small nucleus.
Niels BohrHe present a picture of atom structure