Timeline Of The Discovery Of The Atom

Question 1

In 420 BC, who believed what about the atom?

Answer 1

Democritus believed matter to be composed of small particles with empty space between them

Question 2

Who and when discovered the electron? What did it lead to?

Answer 2

In 1897, by Jj thompson

Lead to the plum pudding model

Question 3

What did the plum pudding model suggest?

Answer 3

The atom was a ball of positive charge with negative electrons embedded in it

Question 4

In 1909, which three people devised which experiment?

Answer 4

Geiger, Marsdon and Rutherford devised the scattering experiment

Question 5

What did the scattering experiment involve?

Answer 5

Firing alpha particles at very thin gold foil

Question 6

What was the prediction of the scattering experiment?

Answer 6

All of the positively charged alpha particles would be deflected a few degrees by the positive pudding of the atom

Question 7

What actually happened in the scattering experiment?

Answer 7

Vast majority of the particles passed through, some particles bounced back 180 degrees

Question 8

What did the evidence of the scattering experiment suggest?

Answer 8

• The mass of the atom lay mostly at the centre of the nucleus with the rest being mostly empty space
• as most particles had been repelled it suggested the nuclei of the gold atom must have been positively charged

Question 9

What new model replaced the plum pudding theory?

Answer 9

The nuclear model

Question 10

In 1913, who adpated the nuclear model and what did it suggest?

Answer 10

Neils Bohr, suggested the electrons orbit the nucleus in set distances or levels

Question 11

Whose theoretical calculations agreed with the theory?

Answer 11

Bohr’s

Question 12

What ideas did later experiments lead to?

Answer 12

The postive charge of any nucleus is made from smaller positive particles, each with the same sized charge

Question 13

What were the smaller positively charged particles called?

Answer 13

Protons

Question 14

In what year did James chadwick discover a third part?

Answer 14

In 1933, he discovered the existence of a third particle the neutron

Question 15

Where was the neutron found?

Answer 15

In the nucleus with the protons but had no charge

Question 16

What do atoms have a radius of?

Answer 16

1x10-10m

Question 17

What is the radius of the nucleus?

Answer 17

LESS THAN 1x10-14m

Question 18

What is the mass number always? What is the exception?

Answer 18

Mass number is always bigger than the atomic number

Expect for hydrogen were they are the same

Question 19

What does all of the atoms identity depend on?

Answer 19

The number of protons

Question 20

What are both neutrons and protons called?

Answer 20

Nucleons because they both exist in the nucleus

Question 21

Why did most of the alpha particles from the scattering experiment pass through?

Answer 21

The atom was mostly empty space

Question 22

What are the similarities and differences between the plum pudding model and modern nuclear model?

Answer 22

Similarities - both have a area of positive charge, both have electrons, both say the overall charge is neutral
Differences - PPM says positive charge isnt divided into smaller parts, PPM has no neutrons only electrons, PPM has mass spread evenly, but nuclear model has mass concentrated at the nucleus