P4: Atomic Structure

Question 1

Roughly how large is the radius of an atom?

Answer 1

1 x 10^-10

Question 2

What is the relative charge of a proton?

Answer 2

+1

Question 3

What is the relative charge of an electron?

Answer 3

-1

Question 4

Why do atoms have no overall charge?

Answer 4

they have an equal number of protons and neutrons

Question 5

How might the energy level of an electron change when it emitted or absorbs electromagnetic radiation?

Answer 5

-absorbing electromagnetic radiation moved electrons to a higher energy level
-electromagnetic radiation is emitted when an electron drops to a lower energy level

Question 6

What is an isotope?

Answer 6

an atom of the same element but with different numbers of neutrons

Question 7

What does a difference in the number of neutrons change about the symbol of an element?

Answer 7

changes the mass number

Question 8

Who discovered the electron and when?

Answer 8

JJ Thompson in 1897

Question 9

What is the plum pudding model?

Answer 9

a model of the atom which depicts it as a ball of positive charge with electrons embedded in it

Question 10

In Rutherford and Marsden’s experiment, why were some alpha particles reflected back?

Answer 10

-they must have been repelled by the same charge that the alpha particles carried
-the repelling charge must have been much heavier than the alpha particle, or the alpha particle would have passed through

Question 11

Why might some atomic nuclei give out radiation?

Answer 11

they are unstable and giving off radiation allows them to become more stable

Question 12

What determines the type of radiation given off?

Answer 12

why the nucleus is unstable and is also a random process because it is not possible to predict exactly when an atom will decay

Question 13

What is the activity of a radioactive source?

Answer 13

the rate at which it decays (measured in becquerels Bq)

Question 14

What is one becquerel equivalent to?

Answer 14

one decay per second

Question 15

What is the count rate?

Answer 15

the number of decays recorded each second by a detector

Question 16

What are the three main types of nuclear radiation?

Answer 16

alpha, beta and gamma

Question 17

What are the attributes of alpha radiation?

Answer 17

-two neutrons and two protons (helium nucleus)
-ejected from the nucleus
-highly ionising
-absorbed by a few cm of air or a thin sheet of paper
-highly likely to be absorbed and cause damage if passing through living cells

Question 18

What are the attributes of beta radiation?

Answer 18

-high speed electron
-ejected from the nucleus as a neutron turns into a proton
-absorbed by a few mm of aluminium
-reasonably ionising
-likely to cause damage if absorbed by living cells
-can penetrate the body to inner organs

Question 19

What are the attributes of gamma radiation?

Answer 19

-electromagnetic radiation
-emitted from the nucleus
-least ionising
-needs many cm of lead or many m of concrete to absorb most of it
-likely to pass through living cells without being absorbed and causing ionisation

Question 20

What is the fourth type of nuclear radiation?

Answer 20

a neutron which can be emitted during radioactive decay

Question 21

What is radioactive contamination?

Answer 21

the unwanted presence of materials containing radioactive atoms on other materials

Question 22

What is irradiation?

Answer 22

-the process of exposing an object to nuclear radiation
-can be deliberate or accidental
-does not cause the object to become radioactive

Question 23

What is the difference between a contaminated and an irradiated object?

Answer 23

a contaminated object continues to give out radiation until decontaminated and an irradiated object does not become radioactive

Question 24

How can you protect against unwanted irradiation?

Answer 24

-using sources of the lowest possible activity for the shortest amount of time possible
-wearing appropriate protective clothing
-not handling sources with bare hands

Question 25

Would food contaminated with an alpha source be more hazardous than food contaminated with a gamma source and why?

Answer 25

yes because alpha is more strongly ionising