Atomic Structure

Question 1

What happens in an atom when electromagnetic radiation is absorbed?

Answer 1

An electron moves into a higher energy level (further away from the nucleus).

Question 2

How many times bigger is the radius if the atom than the radius of the nucleus?

Answer 2

More 10000.

Question 3

Where is most of the mass concentrated in an atom?

Answer 3

Nucleus

Question 4

What are isotopes?

Answer 4

Atoms of the same element that have different numbers of neutrons.

Question 5

Describe Thomson’s Plum Pudding Model.

Answer 5

• Mass and positive charge are spread evenly throughout the atom.
• Negatively charged electrons are embedded within the atom.

Question 6

Describe Rutherford’s Nuclear Model.

Answer 6

• All the positive charge and most of the atom’s mass concentrated within a tiny central nucleus.
• Except for orbiting electrons, the atom is mostly empty space.

Question 7

Describe how the alpha particle scattering experiment led to the replacement of the plum pudding model by the nuclear model.

Answer 7

All of the fast moving positively charged alpha particles would have passed straight through the gold foil of the plum pudding model was correct. Some alpha particles were deflected and a few were repelled straight back. This led to the nuclear model idea that atomic mass is concentrated in a positively charged centre.

Question 8

Describe the Bohr model.

Answer 8

Electrons are organised into energy levels at specific distances from the nucleus.

Question 9

What did Chadwick discover?

Answer 9

The neutron.

Question 10

What is radioactive decay?

Answer 10

A random process that happens when an unstable atomic nucleus gives out nuclear radiation to become more stable.

Question 11

What is activity?

Answer 11

The rate at which a source of unstable nuclei decays. It is measured in becquerel (Bq).

Question 12

What is count rate?

Answer 12

The number of decays recorded each second by a detector.

Question 13

Alpha Particle:
- structure
- range
- change when particle is emitted
- absorbed by
- ionising power

Answer 13

• A helium nucleus
• < 5cm
• loses 2 protons and 2 neutrons
• Paper/skin
• Most strongly ionising

Question 14

Beta Particle:
- structure
- range
- change when particle is emitted
- absorbed by
- ionising power

Answer 14

• High speed electron
• 1 metre
• A neutron turns into a proton
• 5mm of Aluminium
• Low

Question 15

Gamma Ray:
- structure
- range
- change when particle is emitted
- absorbed by
- ionising power

Answer 15

• High frequency electromagnetic radiation
• Infinite
• No change
• Lead
• Very low

Question 16

What is ionising power?

Answer 16

The ability of the radiation to change an uncharged atom into a charged one.

Question 17

What are the two ways that nuclear radiation can be detected and measured.

Answer 17

A Geiger-Muller tube measures the count-rate when connected to a rate-metre.
Photographic Film turns foggy into the presence of radiation.

Question 18

How is an alpha particle shown as in a nuclear equation?

Answer 18

4
He
2

Question 19

How is a beta particle shown in a nuclear equation?

Answer 19

0
e
-1

Question 20

Why does the emission of a gamma ray not cause the mass or the charge of the nucleus to change?

Answer 20

Gamma rays are electromagnetic radiation so have no mass and no charge.

Question 21

What is half-life?

Answer 21

• The time it takes for the number of nuclei of the unstable isotope in a sample to halve
• The time it takes for the count rate, or activity, of a sample to halve.

Question 22

Radioactive isotopes with longer half-lives are described as having …

Answer 22

More stable nuclei.

Question 23

What is net decline expressed as a ratio?

Answer 23

Activity after n half-lives : initial activity
Where n represents a number of half-lives.

Question 24

What is contamination?

Answer 24

The presence of materials containing radioactive atoms on or in other materials.

Question 25

What is irradiation?

Answer 25

When an object is exposed to nuclear radiation.

Question 26

What are examples of suitable precautions?

Answer 26

• Wearibg protective clothing
• Minimising unnecessary exposure
• Handling radioactive material with tongs

Question 27

What are the hazards associated with contamination?

Answer 27

• The exposed object will also become contaminated so will emit radiation
• Alpha particles inside the body are very ionising

Question 28

What is a hazard associated with irradiation and how can it be prevented?

Answer 28

• The greater the distance away from the source and the less time spent near it, the lower the irradiation
• The more ionising radiation can cause tissue damage