1. Subatomic Particles and the Nuclear Atom

2. Discovering the Electron William Crooke - Scientists were working in the lab with a tube filled with gas and they noticed that there were particles traveling from the cathode to the anode of the tube - Called this the cathode ray tube - They tried different gases and got the same results - A cathode ray is a stream of charged particles - The particles carry a (-) charge J.J. Thompson -

3. Subatomic Particles and the Nuclear Atom Electron – negatively charged particles that are part of all forms of matter This apparatus led to invention of television

4. Subatomic Particles and the Nuclear Atom Scientist continued work with cathode ray tubes and by the end of 1800s they were convinced of the following: –Cathode rays were actually a stream of charged particles –The particles carried a negative charge. (the exact value of the negative charge was not known, however.) Because changing the type of electrode or varying the gas in the cathode ray tube did not affect the cathode ray produced, it was concluded that the rays negative particles were found in all forms of matter.

5. Subatomic Particles and the Nuclear Atom Robert Millikan – oil drop experiment to discover the mass of an electron. Mass of e - = 9.1 x 10 -28 g Thompson – Plum Pudding Model The atom is a mass of positive charge that has negative charges evenly distributed throughout a uniform positive charge.

6. Subatomic Particles and the Nuclear Atom

7. Ernest Rutherford (1871-1937) In 1911 Rutherford became interested in studying how positively charged alpha particles interacted with solid matter. A group of scientist that included Rutherford conducted experiments to see if alpha particles would be deflected as they passed through a thin foil of gold

8. Subatomic Particles and the Nuclear Atom Rutherford thought that there would be only minor deflections of alpha particles by the electrons. Rutherfords assumptions were based on Thompson's plum pudding model.

9. Subatomic Particles and the Nuclear Atom

10. This is what Rutherford observed: http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruth er14.swfhttp://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruth er14.swf

11. Subatomic Particles and the Nuclear Atom He concluded that the plum pudding model was incorrect! Rutherford knew there was something dense in the atom that was deflecting the alpha particles Nucleus – a dense mass located within the atom that contains all (+) charges and almost all the mass of the atom

13. Subatomic Particles and the Nuclear Atom By 1920, eight years after his gold foil experiment he concluded that the nucleus contained positively charged particles. Proton – subatomic particle carrying a charge equal to but opposite that of an electron (+)

14. Subatomic Particles and the Nuclear Atom James Chadwick: –Co-worker of Rutherford that showed nucleus contains neutral particles called neutrons Neutron – neutral particle in the nucleus of an atom with a mass nearly equal to that of a proton http://trshare.triumf.ca/~safety/EHS/rpt/rpt_1/node7.html