The model of the atom

Question 1

Where was Democritus from?

Answer 1

Greece

Question 2

What century was Democritus from?

Answer 2

500BC

Question 3

What was the first major theory about atoms called?

Answer 3

Atomic theory

Question 4

What is atomic theory?

Answer 4

Everything is made up of tiny particles that can’t be broken down any further. They are separated from each other by empty space.

Question 5

Who came up with atomic theory?

Answer 5

Democritus

Question 6

What theory did John Dalton propose?

Answer 6

That atoms are solid spheres, and different types of spheres make up different elements.

Question 7

What century was John Dalton from?

Answer 7

1800’s

Question 8

Who came up with the plum pudding model?

Answer 8

JJ. Thompson

Question 9

What year did JJ. Thompson come up with his theory?

Answer 9

1897

Question 10

What particles did JJ. Thompson discover?

Answer 10

Electrons

Question 11

Describe the plum pudding model

Answer 11

The atom is a ball of positive charge, with discrete electrons stuck in it (like plums in a pudding)

Question 12

Who came up with a theory in 1909?

Answer 12

Earnest Rutherford

Question 13

What experiment did Earnest Rutherford conduct that led to his theory?

Answer 13

He took positively charged alpha particles, and he fired them at a thin sheet of gold.

Question 14

What did Earnest Rutherford say the alpha particles should do in his experiment?

Answer 14

If the positive charge in the gold atoms was generally spread out, as in the plum pudding model, then the alpha particles should pass through the sheet of gold, because the weak spread out positive charge wouldn’t be strong enough to affect them.

Question 15

What happened to the alpha particles in Rutherford’s experiment?

Answer 15

Some of the alpha particles were deflected to the side, whilst a small number were deflected back the way they had come.

Question 16

What model did Rutherford come up with after his experiment?

Answer 16

The nuclear model

Question 17

Describe the nuclear model.

Answer 17

Instead of a general field of positive charge, there is a compact nucleus that contains all of the positive charge of the atom. The negative charge exists in a cloud around the central nucleus.

Question 18

What flaw did Rutherford’s nuclear model have?

Answer 18

There was nothing stopping the cloud of electrons from rushing in towards the positive nucleus, so the atom should just automatically collapse, which we know doesn’t happen.

Question 19

Who found a solution to Rutherford’s model in 1913?

Answer 19

Niels Bohr

Question 20

What was Niels Bhor’s solution to Rutherford’s problem?

Answer 20

The electrons orbit the nucleus, like how planets orbit the sun. They are held in shells.

Question 21

How does Niels Bhor’s theory fix the problem in Rutherford’s?

Answer 21

The orbitting of the electrons prevents the atom from collapsing.

Question 22

What did further experiments Rutherford conducted find?

Answer 22

The positive charge in the nucleus is made up of small discrete particles, now known as protons.

Question 23

What particles did James Chadwick discover?

Answer 23

Neutrons (neutral particles in the nucleus)