Atomic Models

Question 1

Why were different models of the atom accepted in the past?

Answer 1

Because they fitted the evidence available at the time.

Question 2

Why were new models of the atom developed?

Answer 2

Because scientists did more experiments, so new evidence was found and the old models were modified to fit it.

Question 3

What models of the atom do we need to know?

Answer 3

• John Dalton’s
• J.J. Thompson’s
• Ernest Rutherford’s
• Niels Bohr’s

Question 4

When did Dalton create his model of the atom?

Answer 4

At the start of the 19th century.

Question 5

What was Dalton’s model of the atom?

Answer 5

He described atoms as solid spheres and said that different spheres made up the different elements.

Question 6

What did Dalton’s model of the atom look like?

Answer 6

image

Question 7

When did Thompson create his model of the atom?

Answer 7

In 1897.

Question 8

What did Thompson conclude from his experiments?

Answer 8

That an atom must contain even smaller, negatively charged particles - electrons.

Question 9

What was Thompson’s model of the atom?

Answer 9

It was known as the ‘plum pudding model’.

Question 10

What did Thompson’s model of the atom look like?

Answer 10

image

Question 11

When did Rutherford create his model of the atom?

Answer 11

in 1909.

Question 12

Who helped Rutherford create his model of the atom?

Answer 12

His students:
•Hans Geiger.
•Ernest Marsden.

Question 13

How did Rutherford create his model of the atom?

Answer 13

He conducted his famous gold foil experiment.

Question 14

How did Rutherford’s gold foil experiment work?

Answer 14

He fired alpha particles (which are positively charged) at a very thin gold sheet.

Question 15

What was Rutherford expecting the alpha particles to do in the experiment?

Answer 15

Because of the plum pudding model, he expected that most of the alpha particles would be deflected slightly by the positive ‘pudding’ that made up most of the atom.

Question 16

What did the alpha particles actually do in Rutherford’s experiment?

Answer 16

Most of them passed straight through the gold atoms and a very small number were deflected backwards.

Question 17

What did Rutherford conclude from his experiment?

Answer 17

That the plum pudding model couldn’t be correct.

Question 18

What did Rutherford use the results from his experiment to do?

Answer 18

He came up with a model of the atom that could explain this new evidence.

Question 19

What was Rutherford’s model of the atom called?

Answer 19

The nuclear model of the atom.

Question 20

What was Rutherford’s nuclear model of the atom?

Answer 20

A tiny, positively charged nucleus at the centre, surrounded by a ‘cloud’ of negative electrons with most of the atom being empty space.

Question 21

What did Rutherford’s model of the atom look like?

Answer 21

image

Question 22

When did Bohr create his model of the atom?

Answer 22

in 1913.

Question 23

What did scientists realise about Rutherford’s model?

Answer 23

That electrons in a ‘cloud’ around the nucleus of an atom would quickly spiral down into the nucleus, causing the atom to collapse.

Question 24

What did Bohr do after scientists realised Rutherford’s electrons in a ‘cloud’ could not work?

Answer 24

He proposed a new model of the atom with four basic principles.

Question 25

What were the four basic principles of Bohr’s model of the atom?

Answer 25

• Electrons can only exist in fixed orbits (shells) and not anywhere in between.
• Each shell has a fixed energy.
• When an electron moves between shells, electromagnetic radiation is emitted or absorbed.
• Because the energy of the shells is fixed, the radiation will have a fixed frequency.

Question 26

What observations did the Bohr model also fit?

Answer 26

Because the frequencies of radiation emitted and absorbed by atoms were already known from experiments, the model fitted the results.

Question 27

What did Bohr’s model of the atom look like?

Answer 27

image

Question 28

What did scientists later discover and do about the Bohr’s model?

Answer 28

That not all the electrons in a shell had the same energy so they refined the model to include sub-shells.

Question 29

What is good about the refined Bohr’s model?

Answer 29

It fits observations better than the original Bohr’s model (even though it is still not perfect).

Question 30

What is the refined Bohr’s model used to do?

Answer 30

Describe atoms, because it explains many observations from experiments (e.g. bonding and ionisation energy trends).

Question 31

What is the most accurate model of the atom that we have today?

Answer 31

A model based on quantum mechanics.

Question 32

What does the model of the atom based on quantum mechanics do?

Answer 32

It explains observations that cant be accounted for by the refined Bohr’s model.

Question 33

Which model of the atom do scientists use?

Answer 33

Either the refined Bohr’s model or the model of the atom based on quantum mechanics (whichever is relevant to the investigation).