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Rutherford Experiment and Atomic Structure. New Models of the Atom. The Dalton Model. p. p. p. p. p. p. p. The Thomson Model. Rutherford Experiment. Lead Block. Alpha Particles. Very thin sheet of Gold. Radioactive Source. Screen for detecting Particles. Experimental Notes.
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New Models of the Atom The Dalton Model p p p p p p p The Thomson Model
Rutherford Experiment Lead Block Alpha Particles Very thin sheet of Gold Radioactive Source Screen for detecting Particles
Experimental Notes • Alpha Particles are very small, “heavy” and positively charged radiation particles • They are heavier than protons, but lighter than most atoms • The gold foil is really, really thin, just a few atoms thick • When the alpha particles hit the screen, they would give a little flash of light…one could sit back and count the flashes from different parts of the screen LeadBlock Alpha Particles Very thin sheet of Gold RadioactiveSource Screen for detecting Particles
p p p p p p p p Thomson Model: Expected Results Gold Atom Protons Scattered Through Nucleus Particles “sprayed” out AlphaParticles
Rutherford Experiment Gold Atom A few get scattered a bit AlphaParticles Most Protons Go Straight Through Nucleus A very few get “bounced” completely
Interpretations Gold Atom A few hit the nucleus on the side AlphaParticles nucleus Most protons missed the nucleus A very few “bounced” completely off the nucleus
Interpretations • Given that the vast majority went straight through the atom, the nucleus must be very, very small. • The fact that some of the alpha particles bounced off completely meant that all the protons must be concentrated at one point. • So that “one point”, the nucleus, must be very small, heavy, and so very very dense. • The rest of the volume of the atom must be filled with the left over material, the electrons
The atom starts to look a little weird…. • The great majority, 99.95%, of the mass is in the nucleus • The nucleus is really tiny, about 0.0000000000001 % of the volume of the atom • The great majority, 99.9999999999999 % of the volume of the atom is electron space • But that part has almost no mass
An Analogy…for an atom of carbon Imagine that a nucleus was the size of a lead marble… Place it in middle of Giant stadium The rest of the volume of the atom would be filled with six fleas, flying around inside the stadium
Measurements of the atom The nucleus is about 0.000001 nanometers wide { About 0.2 nanometers wide