Atomic structure

Question 1

Briefly explain how the model of an atom has changed over time

Answer 1

First thought atoms were tiny spheres that couldnt be broken up. Then the plum pudding model was discovered suggesting they were small spheres of positive charge with electrons in them. This was proven wrong when the first nuclear model of the atom was discovered.

Question 2

What happens to an electron in an atom if it releases EM radiation

Answer 2

It will move to a lower energy level closer to the nucleus. Opposite if it absorbs EM radiation.

Question 3

Who provided evidence to suggest the existence of the neutron

Answer 3

James Chadwick

Question 4

What happens to an atom if it loses one or more is electrons

Answer 4

It becomes a positive ion

Question 5

Which number defines what element an atom is

Answer 5

The atomic number

Question 6

What is the atomic number of an atom and what is the mass number of an atom

Answer 6

The atomic number is the number of protons in an atom. The mass number is the number of protons + number of neutrons (mass of nucleus)

Question 7

What is an isotope and are they usually stable

Answer 7

Isotopes of an elements are atoms with the same number of protons but a different number of neutrons. Most elements only have on or two stable ones others decay.

Question 8

What is radioactive decay

Answer 8

The decay of unstable isotopes that give out radiation as they try to become more stable

Question 9

Name four things that may be emitted during radioactive decay

Answer 9

Alpha radiation
Beta radiation
Gamma radiation
Neutrons

Question 10

For the three types of ionising radiation give: Their ionising power and range in air

Answer 10

Alpha-Strongly ionising, only a few cm in air
Beta-moderately ionising, a few metres in air
Gamma-weakly ionising, will travel a long distance through air

Question 11

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

Answer 11

Alpha radiation is immediately absorbed by the material

Question 12

What type of nuclear decay doesnt change the mass or charge of the nucleus

Answer 12

Gamma rays

Question 13

What is the activity of a source and what are its units

Answer 13

The rate at which a source decays, measured in becquerels Bq (1 Bq is 1 decay per second)

Question 14

Define half life

Answer 14

Half life is the time taken for the number of radioactive nuclei in an isotope to halve.

Question 15

What does a short half life mean

Answer 15

A short half life means activity falls quickly because nuclei are unstable and decay quickly. High amounts of radiation are emitted at the start

Question 16

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

Answer 16

It releases small amounts of radiation for a long time, therefore nearby areas are exposed to radiation for millions of years.

Question 17

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

Answer 17

The half life is found from the graph by finding the time interval at the halving of the activity on the vertical axis

Question 18

Define radiation dose

Answer 18

It tells you the risk of harm to body tissue due to exposure to radiation measured in sieverts

Question 19

State two aspects of your lifestyle that can affect your radiation dose

Answer 19

Where you live and if you have a job that involves radiation

Question 20

Define irradiation and contamination

Answer 20

Irradiation-Objects near a radioactive source are irradiated by it, meaning they are exposed to it.
Contamination-When unwanted radioactive atoms get onto or into an object

Question 21

Compare the hazards of being irradiated and contaminated by an alpha source and a gamma or beta source

Answer 21

Beta and gamma sources are most dangerous outiside the body as it can penetrate the body and get to the delicate organs.
Alpha radiation is most dangerous inside the body as they do all their damage in a very localised areas.

Question 22

Give two examples of how to protect against contamination and irradiation

Answer 22

Irradiation-keeping sources in lead lined boxes, standing behind barriers or being in a different room
Contamination-Gloves and tongs should be used when handling sources, protective suits should be worn to prevent particles being breathed in.

Question 23

Describe some of the risks involved with using radiation

Answer 23

Radiation can enter living cells and ionise atoms and molecules with them which can lead to tissue damage.
Lower doses tend to cause mutant cells (cancer) and higher doses tend to kill cells completely causing radiation sickness

Question 24

Give two ways that radiation is used in medicine

Answer 24

Medical tracers-Radioactive isotopes can be injected into people and their progress around the body can be followed.
Radiotherapy-Gamme rays are directed carefully and at just the right dosage to kill the cancer cells without damaging too many normal cells.

Question 25

Define fission and fusion

Answer 25

fission-Nuclear reaction that is used to release energy from large unstable atoms by splitting them into smaller atoms
Fusion-Nuclear reaction in which two light nuclei collide at high speed and join to create a larger heavier nucleus which releases energy

Question 26

Is fission usually spontaneous

Answer 26

No because the nucleus has to absorb a neutron before it will split

Question 27

Describe what a chain reaction is and what happens when it is uncontrolled

Answer 27

In fission two or three neutrons are released and if these are moving slow enough to be abosrbed by another nucleus more fission can occur causing a chain reaction. If they arent controlled lots of energy is released as an explosion.

Question 28

How does fusion release energy

Answer 28

When the nuclei fuse some of the mass of the lighter nuclei is converted to energy released as radiation as well as released a high energy neutron.