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Rutherford
The Gold Foil and the Nucleus
Gold Foil Model
The J.J. Thomson Model
“Plum Pudding Model”
• The pudding was thought to be positively charged
• The negatively charged “Plums” (electrons) were believed to
be spread evenly throughout the atom
The Apparatus
What is an “Alpha Particle”
• An alpha particle consists of 2 protons and 2 neutrons with a
mass much greater than an electron
Observation
• According to Thomson, the Alpha particles should have passed
right through
When some of the particles
bounced straight back, he
concluded that there must be
something with a much greater
mass at the center of the atom!
The Outcome
• Rutherford's three observations:
• Most alpha particles passed straight through the foil.
• Some were deflected through angles less than 90 degrees.
• A very small proportion of particles were deflected through
angles greater than 90o.
• His three subsequent conclusions:
• Most of the atoms are empty space.
• The alpha particles have an overall positive charge, forcing
them to be repelled away from the metal atoms in the foil.
• The atoms in the foil have a large, dense nucleus in their
centers.
A New Atomic Model