Rutherford and Bohr Rutherford – Structure of the Atom

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Presentation transcript:

Rutherford and Bohr Rutherford – Structure of the Atom Remember the existing model of atom is the Plum pudding model from JJ Thomson Have electrons and everything else is postive So Rutherford does experiment that is outlined on the next slide

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Sir Rutherford’s Experiment Shot alpha (+) particles at gold leaf (small # of atoms thick) Around gold leaf placed chemical coated material that detected presence of alpha particles by showing a green glow The experiment was run for days and his graduate student kept track of the location and number of green glows.

Sir Rutherford’s Gold Foil Experiment Results Angle of deflection (degrees) # of deflection 0-5 (straight thru) 8,289,000 10 502,570 15 120,570 30 7,800 45 1,435 60 477 75 211 >105 (bounced back) 198 What does lab data tell use: 1) 0-5degree shows that 8 out of 9 particles went right thru. Result – atom is mostly empty space 2) >105 degree shows that there must something in atom very massive (i.e. high mass). Result – small volume massive center 10-75degree mean that the particle are deflected from their straight path. Result – Since particle is + charge must be going by a postive charge

Sir Rutherford’s Gold Foil Experiment So what does this tell us. Rutherford discovered in the atom: 1) A small volume (compared to the volume atom) 2) Massive (high mass area) 3) Positively charge Rutherford called it the “nucleus”. His experiment did not discover anything about the electrons. He postulated that the electrons are moving around the nucleus like the planets around the sun. THIS IS WRONG. We call it RUTHERFORD SHORTCOMING. WHY IS IT WRONG????

Rutherford’s shortcoming He says that the electrons (a negative particle) will move around the nucleus (positive particle) in a specific path without energy change. Problem: It breaks the laws of physics. Without getting too physic specific, this can’t happen without the electron doing one or two things: 1) spiraling into the nucleus due to coulombic force attraction 2) you constantly giving energy to the electron to counterbalance the coulombic force attraction so it stays at specific distance from nucleus. SO WHAT DID RUTHERFORD’S GOLD LEAF EXPT SHOW: Answer: Structure of the atom, small massive “+” charge center called nucleus His explanation of electron movement IS WRONG