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

3) 10-75degree mean that the particle are deflected from their straightpath. 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 planetsaround 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