3 Democritus 400 BC Proposed that all matter is made up of atoms. Thought atoms were small, hard particles of different shapes and sizes.Coined the term ‘Atom’From the Greek word meaning‘Can not be divided.’
7 Lavoisier 1785 Authored the Law of Conservation of Mass Did experiments to prove that matter does not disappear during a chemical reaction.‘Matter can not be created or destroyed, it can only be rearranged.’
9 Dalton Father of Modern Atomic Theory 1800’s All matter consists of atoms with space in between.Atoms of the same kind of element are identical to each other.There are as many different kinds of atoms as there are different elements.Atoms are solid spheres.‘Billiard Ball Model’
12 Thomson1904Inferred that atoms contain small negatively charged particles.He called them ‘electrons.’He thought the electrons were dispersed throughout a positively charged sphere.‘Chocolate Chip Cookie Dough Model’
15 Rutherford 1911 Famous Gold Foil Experiment Discovered and named the ‘nucleus’ of the atom.Proposed that most of the mass and all of the positive charges of an atom are in its nucleus.‘Peach Pit Model’
22 Schrodinger and Heisenburg 1926Scientists described the electron region of the atom as a cloud around the nucleus.This cloud area shows that electrons do not orbit the nucleus in definite paths, but are likely to be in a given region at any particular time.‘Modern Electron Cloud Model’
25 Chadwick1932Worked with E. Rutherford in the discovery of a third sub-atomic particle.He concluded this particle to be free of electrical charge and he called it the ‘neutron.’Concluded it was located in the nucleus along with the protons.