Discovery Of The Nucleus Flashcards
Who discovered the nucleus?
Ernest Rutherford
What did Ernest Rutherford discover?
The nucleus
What did Rutherford study?
The scattering of alpha particles by a very thin sheet of gold foil
What are alpha particles?
Positively charged particles produced by certain radioactive substances
Describe the apparatus Rutherford used.
7
A radioactive source held away from a thin sheet of gold foil
The gold foil is between the radioactive source and a fluorescent screen used to detect alpha particles
Alpha particles are emitted by the radioactive source
Some alpha particles were deflected back along their own path when they hit the gold foil
Some alpha particles were deflected at an angle when they hit the gold foil
Most alpha particles passed through the gold foil with little or not deflection and hit the fluorescent screen
Some alpha particles passed through the gold foil but were deflected at large angles and hit the fluorescent screen away from the centre
What did Rutherford do to the gold foil?
He bombarded a thin piece of gold foil with alpha particles
What did Rutherford bombard with alpha particles?
A thin piece of gold foil
What do alpha particles consist of?
Groups of two neutrons and two protons stuck together
What would you expect to happen during Rutherford’s experiment if Thompson’s model of the atom was correct?
(2)
You would expect to find that some of the alpha particles would be deflected by small amounts
I.e. if the positive charge were distributed throughout the atom, the alpha particles would suffer only slight deflections when they met one of these positive charges as they passed through the atom
What type of screen did Rutherford use?
A phosphorescent screen made of zinc sulfide
What happens when an alpha particle strikes the screen?
A little flash of light appears on the screen
How did Rutherford observe the flashes of light on the screen?
Through a microscope
What did Rutherford find from his experiment?
2
He found that some alpha particles were deflected at large angles as they passed through the gold foil
He also found that some alpha particles were deflected back along their own path
What did Rutherford conclude from his experiment?
The positive charge and the mass of the atoms of the metal foil were concentrated in a small dense core called the nucleus of the atom
According to Rutherford, what is a nucleus?
A small dense core where the positive charge and the mass of the atom are concentrated
What evidence did Rutherford have to back up his conclusion on the nucleus?
(4)
The positively charged alpha particles and the positively charged nucleus repelled each other
Some alpha particles were reflected back along their original paths when they collided head on with the nucleus
The deflection of the alpha particles at large angles was caused by the alpha particles coming very close to the high concentration of positive charge in the nucleus and being repelled by this charge
Only a small number of alpha particles were reflected back along their original paths because the positive charge and mass of the atoms of the metal were concentrated in such a small dense core
What does the positively charged nucleus repel?
The positively charged alpha particles
When were the alpha particles reflected back along their original paths?
When they collided head on with the nucleus
What caused the deflection of the alpha particles at large angles?
It was caused by the alpha particles coming very close to the high concentration of positive charge in the nucleus and being repelled by this charge
What happened when the alpha particles collided head on with the nucleus?
They were reflected back along their original paths
What happened when the alpha particles came close to the nucleus?
They were deflected at large angles
Why were only a small number of alpha particles reflected back along their original paths?
As the positive charge and mass of the atoms of the metal were concentrated in such a small dense core
From careful study of the scattering of particles, what was Rutherford and his team able to deduece?
They were able to deduce the approximate diameter of the nucleus (1/100,000 of the size of an atom)
What three observations did Rutherford make?
Most alpha particles pass straight through the gold foil
Some alpha particles are deflected at large angles
A small number of alpha particles are reflected back along their own paths
What is the corresponding conclusion for the fact that most alpha particles pass straight through the gold foil ?
Most of the atom is empty space
What is the corresponding conclusion for the fact that some alpha particles are deflected at large angles?
The alpha particles are repelled when they pass near the small positive nucleus
What is the corresponding conclusion for the fact that a small number of alpha particles are reflected back along their own paths
A small number of alpha particles collide head on with the nucleus
What three conclusions did Rutherford make>
Most of the atom is empty space
The alpha particles are repelled when they pass near the small positive nucleus
A small number of alpha particles collide head on with the nucleus
