Topic 4 - Atomic Structure

Question 1

Briefly describe how the model of an atom has changed over time.

Answer 1

• Democritus made the theory that matters is made up of tiny spheres known as ‘atoms’
• Thomson introduces the plum pudding model with spheres of positive charge and tiny negative electrons stuck to them
• Rutherford discovered the nucleus through performing an experiment of firing alpha particles at a thin gold foil
• Bohr refined Rutherford’s nuclear model and made the conclusion that electrons orbited the nucleus in ‘energy levels’ or shells
• Chadwick discovered the neutron.

Question 2

Who provided evidence to suggest the existence of the neutron?

Answer 2

James Chadwick

Question 3

True or False? Atoms have no overall change.

Answer 3

True

Question 4

What happens to an atom if it loses one or more of its outer electrons?

Answer 4

It becomes a positively charged ion

Question 5

Which number defines what element an atom is: The atomic number or the mass number?

Answer 5

Atomic number

Question 6

What is the atomic number of an atom?

Answer 6

The number of protons

Question 7

True or False? Isotopes have different mass numbers.

Answer 7

True

Question 8

What is radioactive decay?

Answer 8

When unstable isotopes decay into other elements and give out radiation as they try to become more stable.

Question 9

Name 4 things that may be emitted during radioactive decay.

Answer 9

• Alpha radiation
• Beta radiation
• Gamma radiation
• Neutrons

Question 10

For alpha, beta, and gamma radiation, give: a). Their ionising power b). Their range in air

Answer 10

a). Alpha is strongly ionising, Beta is moderately ionising and gamma is weakly ionising
b). Alpha has a range of a few cm, Beta has a range of a few metres, and gamma has a long distance of range

Question 11

Explain why alpha radiation could not be used to check the thickness of metal sheets.

Answer 11

It has a very weak penetrating power, and can be absorbed by a sheet of paper.

Question 12

How could you represent alpha radiation in nuclear equations?

Answer 12

A helium nucleus (4/2 He)

Question 13

What type of nuclear decay doesn’t change the mass or charge of the nucleus?

Answer 13

Gamma rays

Question 14

Name a piece of equipment that could be used to measure radiation.

Answer 14

Geiger-Muller tube and counter

Question 15

What is the activity of a source? What are its units?

Answer 15

The number of counts per minute (Bq)

Question 16

Explain the dangers of a radioactive source with a long half-life.

Answer 16

The damaging effects of the radiation lasts too long and the dose received continues to rise.

Question 17

Explain how you would find the half-life of a source, given a graph of its activity over time.

Answer 17

Read the initial activity off the graph. Divide the initial activity by 2 to find the value of half the initial activity. Find this value on the y-axis and read along horizontally to the curve. Then read down the curve at that point to find the half-life.

Question 18

Define radiation dose.

Answer 18

The risk of harm to body tissues due to exposure to radiation (Sv).

Question 19

State 2 aspects of your lifestyle that can affect your radiation dose.

Answer 19

• Occupation
• Location

Question 20

Define irradiation and contamination.

Answer 20

Irradiation= Exposure to radiation
Contamination= Radioactive particles getting onto objects

Question 21

Compare hazards of being irradiated by an alpha source and a gamma source.

Answer 21

Alpha is less dangerous because it can’t penetrate the skin and gets blocked by a small air gap, unlike gamma which is highly penetrable and can get to delicate organs.

Question 22

Give 2 ways that radiation is used in medicine.

Answer 22

• Radiotherapy
• Medical Tracers

Question 23

Describe some of the risks involved with using radiation.

Answer 23

Radiation can enter cells and ionise atoms and molecules within them, which can lead to tissue damage.

Question 24

Define fission and fusion.

Answer 24

Fission = used to release energy from large and unstable atoms by splitting them into smaller atoms.

Fusion = when 2 light nuclei collide and join to create a larger nucleus.

Question 25

True or False? Fission is usually spontaneous.

Answer 25

False

Question 26

Describe what a chain reaction is.

Answer 26

refers to a process in which neutrons released in fission produce an additional fission in at least one further nucleus.

Question 27

Explain the difference between nuclear fission and fusion.

Answer 27

In nuclear fusion, two nuclei of lighter elements combine to create a nucleus of a larger element, whereas in nuclear fission a large nucleus splits into two smaller nuclei