Atomic Model Evolution

George Dalton was the first person to propose an atomic theory.  His model stated: All matter is made up of tiny hard spheres known as atoms Atoms cannot be created or destroyed Atoms cannot be broken down into smaller particles All the atoms in an element are identical

George Dalton's Atomic Theory (1807)

J.J. Thomson's Discovery of the Electron (1897)

Performed many experiments involving applying high voltages across vacuum tubes - which causes the tube to glow These vacuum tubes are known as cathode ray tubes Thomson measured the mass of the particles in these rays Found that they were much lightest than the smallest atom and therefore must consist of sub-atomic particles 

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Rutherford's Discovery of Nucleus (1909)

Before Rutherford's experiments: The atom was considered using the Thomson's Plum Pudding Model - a sphere of positive charge with electrons distributed randomly in it  Rutherford's experiments: Involved bombarding gold foil with positively charged particles known as alpha particles What the atomic model at the time would have predicted:  Most of the alpha particles would be deflected straight back What actually happened: Most of the alpha particles passed straight through, some were slightly deflected and a very small number bounced straight back Rutherford's conclusions: The atom must be mostly empty space, with a positive central nucleus that contains most of the mass This is sometimes known as the Geiger and Marsden experiment as it was carried out by two of Rutherford's assistant with those names.

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Chadwick's Discovery of the Neutron (1932)

James Chadwick discovered the neutron in 1932 This led to the discovery of isotopes and thus nuclear energy

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Nuclear energy

By firing neutrons at U-235, a nucleus can be split in a process called nuclear fission Produces new elements and transfers large amounts of energy This energy is used to produce electricity in nuclear power plants  

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