Discovery Of The Nucleus

Question 1

Who discovered the nucleus?

Answer 1

Ernest Rutherford

Question 2

What did Ernest Rutherford discover?

Answer 2

The nucleus

Question 3

What did Rutherford study?

Answer 3

The scattering of alpha particles by a very thin sheet of gold foil

Question 4

What are alpha particles?

Answer 4

Positively charged particles produced by certain radioactive substances

Question 5

Describe the apparatus Rutherford used.

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Answer 5

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

Question 6

What did Rutherford do to the gold foil?

Answer 6

He bombarded a thin piece of gold foil with alpha particles

Question 7

What did Rutherford bombard with alpha particles?

Answer 7

A thin piece of gold foil

Question 8

What do alpha particles consist of?

Answer 8

Groups of two neutrons and two protons stuck together

Question 9

What would you expect to happen during Rutherford’s experiment if Thompson’s model of the atom was correct?
(2)

Answer 9

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

Question 10

What type of screen did Rutherford use?

Answer 10

A phosphorescent screen made of zinc sulfide

Question 11

What happens when an alpha particle strikes the screen?

Answer 11

A little flash of light appears on the screen

Question 12

How did Rutherford observe the flashes of light on the screen?

Answer 12

Through a microscope

Question 13

What did Rutherford find from his experiment?

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Answer 13

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

Question 14

What did Rutherford conclude from his experiment?

Answer 14

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

Question 15

According to Rutherford, what is a nucleus?

Answer 15

A small dense core where the positive charge and the mass of the atom are concentrated

Question 16

What evidence did Rutherford have to back up his conclusion on the nucleus?
(4)

Answer 16

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

Question 17

What does the positively charged nucleus repel?

Answer 17

The positively charged alpha particles

Question 18

When were the alpha particles reflected back along their original paths?

Answer 18

When they collided head on with the nucleus

Question 19

What caused the deflection of the alpha particles at large angles?

Answer 19

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

Question 20

What happened when the alpha particles collided head on with the nucleus?

Answer 20

They were reflected back along their original paths

Question 21

What happened when the alpha particles came close to the nucleus?

Answer 21

They were deflected at large angles

Question 22

Why were only a small number of alpha particles reflected back along their original paths?

Answer 22

As the positive charge and mass of the atoms of the metal were concentrated in such a small dense core

Question 23

From careful study of the scattering of particles, what was Rutherford and his team able to deduece?

Answer 23

They were able to deduce the approximate diameter of the nucleus (1/100,000 of the size of an atom)

Question 24

What three observations did Rutherford make?

Answer 24

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

Question 25

What is the corresponding conclusion for the fact that most alpha particles pass straight through the gold foil ?

Answer 25

Most of the atom is empty space

Question 26

What is the corresponding conclusion for the fact that some alpha particles are deflected at large angles?

Answer 26

The alpha particles are repelled when they pass near the small positive nucleus

Question 27

What is the corresponding conclusion for the fact that a small number of alpha particles are reflected back along their own paths

Answer 27

A small number of alpha particles collide head on with the nucleus

Question 28

What three conclusions did Rutherford make>

Answer 28

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