History of Atom

• 1897 J.J Thompson discovered electrons and created the Plum Pudding model.
• Plum Pudding - A ball of positive charge, with negative electrons embedded in it.
• 1909 - Ernest Rutheford discovered alpha particles could bounce back off of atoms.
• Rutheford concluded that an atoms mass is concentrated in the nucleus, which contained protons.
• Niels Bohr discovered that electrons orbit the nucleus in shells.
• 1932 - James Chadwick discovered the neutron, which is a particle that has no charge and no mass
• John Newland was the first chemist to devise a periodic table, ordered by the the weight of the element.
• Dimitri Mendeleev left gaps in Newland's table as he realised there may be undiscovered elements.