RutherfordThe 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