Chapter 25: Particles Flashcards
What is Rutherford’s nuclear model of the atom?
A central nucleus with positive protons and neutral neutrons surrounded by orbiting negative electrons.
What experiment did Geiger and Marsden do?
There was a source emitting alpha particles, and they were shot towards a thin slice of gold. When alpha particles hit the screen, it caused scintillations.
What observations did Geiger and Marsden make?
The majority of the alpha particles passed straight through the foil. Some were deflected through a small angle but still passed through the foil. Occasionally, an alpha particle was observed ‘bouncing’ back off the gold foil.
How is nuclear fission used?
A nucleus of U-235 can be split by colliding with a neutron. This released energy in the form of kinetic energy.
What does nuclear fission of U-235 produce?
Two daughter nuclei, and a small number of neutrons
What is a chain reaction?
When split by a neutron, uranium-235 released neutrons. These neutrons can then go on to hit other U-235 nuclei which then do the same thing. This causes a chain reaction.
What is the role of the control rods in fission, when used to generate electricity?
Control rods absorb neutrons, so that the chain reaction can be controlled.
What is the role of the moderator in fission, when used to generate electricity?
It slows neutrons down so that they are are the right speed to split nuclei.
What factors affect the deflection of alpha particles by a nucleus?
Charge and speed
Positive alpha particles were being repelled by a positive charge. The faster they hit, the faster they were repelled.
How did Rutherford’s observation account lead to the current model of the atom?
As most of the particles passed through the foil, most of each gold atom must be empty space.
A rebound meant that the particle had hit something big. He realised that the mass of an atom was concentrated in a very tiny volume in the centre of the atom.
The deflections and rebounds were because the positive charges on the alpha particles were repelled by positive charges in the nuclei.
