Topic 4 - Atomic Structure and Radioactivity

Question 1

Give an approximation for the radius of an atom.

Answer 1

1x10−10 metres

Question 2

Where is most of the mass of an atom concentrated?

Answer 2

In the nucleus.

Question 3

Approximately what proportion of the total radius of an atom is the radius of the nucleus?

Answer 3

1/10000

Question 4

Describe the arrangement of protons, neutrons and electrons in an atom.

Answer 4

• the nucleus contains protons and neutrons
• the is a positive charge
• the nucleus is surrounded by electrons in energy levels

Question 5

energy levels

Answer 5

Electrons lie at different distances from the nucleus (different energy levels).

Question 6

What type of charge does the nucleus of an atom

have? Why?

Answer 6

-The nucleus contains protons and neutrons
=Positive charge

Protons have a positive charge

Neutrons have no charge

Question 7

explain how energy levels affect energy

Answer 7

energy levels which are further away from the nucleus are at a higher energy

Question 8

Give two ways that an atom’s electron arrangement can be changed.

Answer 8

Absorbing electromagnetic radiation

Emitting electromagnetic radiation

Question 9

Explain how an atom’s electron arrangement

changes when it absorbs EM radiation.

Answer 9

atoms can absorb electromagnetic radiation this excites the electrons and cause if to move from a lower energy level to a higher energy level

Question 10

Explain how an atom’s electron arrangement

changes when it emits EM radiation.

Answer 10

when atoms can emit electromagnetic radiation. it loses the energy and returns back to its original energy level

Question 11

How does the ratio of electrons to protons in an atom result in the atom having no overall charge?

Answer 11

●The number of protons is equal to the number of electrons

● Protons and electrons have equal and
opposite charges, so charge cancels

Question 12

What do all forms of the same element have in common?

Answer 12

They all have the same number of protons.

Question 13

What is the name given to the number of protons in an atom?

Answer 13

Atomic Number

Question 14

What is an atom’s mass number?

Answer 14

The total number of protons and neutrons in the atom.

Question 15

What is an isotope of an atom?

Answer 15

isotopes are atoms of the same element that have a different number of neutrons but the same number of protons

Question 16

How do atoms turn into positive ions?

Answer 16

• atoms can lose electrons from their outer shell/energy level
• Electrons are negatively charged
• so the charge of the atom is positive

Question 17

What may lead to a scientific model being changed or replaced?

Answer 17

The discovery of new experimental

evidence which doesn’t agree with the existing theory.

Question 18

How did the plum-pudding model describe the atom?

Answer 18

an atom is a ball of positive charge with negative electrons embedded in it

Question 19

Prior to the discovery of the electron, what was believed about the atom?

Answer 19

atoms cannot be divided

Question 20

1800 john dalton

Answer 20

everything was made of tiny spheres of atoms that could not be divided

Question 21

1897-jj Thomson

Answer 21

discovery of electrons

suggested the plum pudding model

Question 22

Which experiment led to the plum-pudding model being discarded?

Answer 22

Rutherford’s alpha scattering experiment.

Question 23

rutherford discovered that

Answer 23

most of the atom was empty space

Question 24

describe the alpha scattering particle

Answer 24

a beam of alpha particles was fired at a thin gold foil
MOST- alpha particles went straight through
SOME- alpha particles slightly deflected
FEW-alpha particles repelled

Question 25

why did they use gold?

Answer 25

because they were able to hammer the gold out into thin foil

Question 26

State the conclusions of the Alpha-Scattering experiment.

Answer 26

most alpha particles went straight through therefore the atoms are mainly empty space

some alpha particles were deflected therefore the centre of an atom must have a positive charge

some alpha particles repelled so that Most of the mass of the atom is
concentrated at the centre in the nucleus

Question 27

the plum pudding model was replaced for the …

Answer 27

nuclear model

alpha scattering particles took place as well

Question 28

Neil Bohr finalised the theory by

Answer 28

produced the final model of the atom that electrons orbit around the nucleus at a specific distance

Question 29

What did James Chadwick’s experiments on the atom prove?

Answer 29

discovered that the nucleus also contains neutrons these have no overall charge they are neutral

Question 30

so the updated nuclear model concludes that

Answer 30

electrons orbit around the nucleus at a specific point

the positive charge is due to the tiny positive particles called protons

the nucleus also contains neutrons

so atoms have no overall charge

Question 31

Why do unstable nuclei give out radiation?

Answer 31

● Unstable nuclei undergo decay to become more stable

● As they release radiation their stability increases

Question 32

define radioactive decay

Answer 32

some isotopes have an unstable nucleus and to become stable it gives out radiation

Question 33

why can’t scientists predict when a nucleus will decay

Answer 33

radioactive decay is a totally random process

Question 34

Define the activity of an unstable nucleus.

Answer 34

activity is the rate at which a source of unstable nuclei decay

Question 35

What is the unit of radioactive activity?

Answer 35

Becquerel (Bq)

1Bq=1 decay per second

Question 36

Give an example of a detector that may be used to measure count-rate.

Answer 36

Give an example of a detector that may be used to measure count-rate.

Question 37

What is count-rate?

Answer 37

The number of decays per

second

Question 38

State four types of nuclear radiation.

Answer 38

1. Alpha particles
2. Beta particles
3. Gamma rays
4. Neutrons

Question 39

What does an alpha particle consist of?

Answer 39

Two protons and two neutrons

Question 40

an alpha particle is the same as an …

Answer 40

It is the same as a helium nucleus

Question 41

What is the range of an alpha particle through the air?

Answer 41

A few centimetres

Question 42

beta particle

Answer 42

beta radiation is an electron ejected from the nucleus this happens because the neutron splits into protons and electrons

Question 43

where is a beta particle formed?

Answer 43

inside the nucleus when a neutron splits into a proton and an electron

Question 44

gamma particle

Answer 44

gamma rays are electromagnetic radiation that emits from the nucleus

Question 45

properties of alpha particles

Answer 45

• alpha particles can travel few centimetres in air
• weakly penetrating
• stopped by paper
• highly ionising

Question 46

What will stop beta radiation from passing through a point?

Answer 46

● A thin sheet of aluminium

● Several metres of air

Question 47

Describe the nature of radioactive decay.

Answer 47

● Random

● It is impossible to predict which nuclei will decay

Question 48

properties of beta particles

Answer 48

• can travel further they reach around 15 cm
• medium penetration
• stopped by thin sheet of aluminium
• medium ionising

Question 49

properties of gamma particles

Answer 49

• travels very far in air before stopping
• highly penetration
• low ionising
• stopped by lead

Question 50

What will stop beta radiation from

passing through a point?

Answer 50

● A thin sheet of aluminium

● Several metres of air

Question 51

What will stop gamma radiation from passing through a point?

Answer 51

● Several centimetres of lead

● A few metres of concrete

Question 52

Which type of radiation is most ionising?

Answer 52

Alpha radiation.

Question 53

Which type of radiation is the least ionising?

Answer 53

Gamma radiation.

Question 54

State any changes to mass or charge

that occur due to the emission of a gamma-ray.

Answer 54

Both mass and charge remain

unchanged.

Question 55

Nuclear Equations alpha particles :

Answer 55

4(take away 4)
He
2 (take away 2 )

Question 56

Nuclear Equations beta particles

Answer 56

0 (stays the same
e
-1 (add one)

Question 57

rules for alpha decay

Answer 57

the atomic number - number at he bottom decrease by 2

- the mass number decrease by 4

Question 58

the symbol for alpha decay

Answer 58

-4
α
2

Question 59

rules for beta decay

Answer 59

the atomic number increases by one but the mass number does not change

Question 60

Gamma Decay:

Answer 60

Does not cause the mass or charge to change.

this is because in the nucleus the high frequency electronic magnetic wave means that no particles are emitted

Question 61

Define the half-life of a radioactive isotope.

Answer 61

● The time it takes for the number of
unstable nuclei in a substance to halve
● The time it takes for the count rate
from a sample to fall to half its initial level

Question 62

So if 80 atoms fall to 20 over 10mins, the half-life?

Answer 62

o 80/2 = 40
o 40/2 = 20 – so two half lives in 10mins
 So half-life is 5mins

Question 63

What is irradiation?

Answer 63

The process of exposing a material to nuclear radiation

The material does not become radioactive

Question 64

Medical items are irradiated

Answer 64

to kill bacteria

Question 65

what can ionising radiation do

Answer 65

increase the risk of cancer

Question 66

what are the precaution of ionising radiation

Answer 66

• shielding
• lead apron
• radiation monitor
• leave the room

Question 67

What is radioactive contamination?

Answer 67

The presence of unwanted radioactive

nuclei on other materials.

Question 68

Why is it important for the results of studies on the
effects of radiation to be published and shared with
other scientists?

Answer 68

To allow the findings to be
independently checked
This is known as peer review

Question 69

J.J. Thomson discovered this sub-atomic particle in 1897.

Answer 69

electrons

Question 70

James Chadwick discovered this sub-atomic particle in 1932.

Answer 70

neutrons

Question 71

Ernest Rutherford discovered this sub-atomic particle in 1909.

Answer 71

proton

Question 72

what is an ion

Answer 72

ions are charged particles that form when an atom either loses or gains electrons , ions are either positive or negatively charged

Question 73

negative ions

Answer 73

are created when an atom gains electrons

Question 74

positive ions

Answer 74

are created when an atom loses electrons

Question 75

What subatomic particle has to be lost or gained for an atom to become charged?

Answer 75

Electron

Question 76

Detecting Radioactivity

There are three primary ways of detecting radioactivity.

Answer 76

Cloud chamber
Photographic film
Geiger counter (Geiger-Muller tube)

Question 77

How does photographic film detect radiation?

Answer 77

a bright spot appears where ionising radiation hits the film

Question 78

How does the cloud chamber detect radiation?

Answer 78

A cloud chamber is a container full of supersaturated alcohol vapour.

Question 79

how does the Geiger-Muller tube (Geiger counter) detect radiation

Answer 79

Ionising radiation enters a tube full of low-pressure gases.
It ionises the atoms in the gas, knocking electrons out of the atoms.
The gas can now conduct electricity and completes an electric circuit. Current flows between electrodes.
The current produces a clicking noise.
The count-rate is the number of decays recorded each second.

Question 80

Practical Applications of Radiation-gamma

Answer 80

Sterilisation

We can use gamma radiation to sterilise medical equipment in hospitals. Sterilisation kills bacteria and viruses.

Question 81

Practical Applications of Radiation-alpha radiation

Answer 81

Smoke detectors
A radioactive material fires alpha particles at a smoke detector.
If there is smoke between the radioactive material and the smoke detector, then fewer alpha particles will reach the detector.
This will set off the smoke alarm.

Question 82

How is blood flow in the body imaged using radiation?

Answer 82

Gamma-emitting isotopes are injected into the body.
We can trace the gamma-emitting particles as they travel in the blood around the body.
We can use the detected signal to image the organs in the body.

Question 83

Adjusting for background radiation

Answer 83

substance radiation=total radiation−background radiation then divide 2

Question 84

If the background count rate is 85, and the initial count rate is 1065, what is the count rate at the half-life?

Answer 84

Substance initial count rate = 980.

So half-life is the time when the corrected count rate is 490, or the uncorrected count rate is 575.

Question 85

further away it is from the nucleus

Answer 85

the higher the energy level

Question 86

the closer it is to the nucleus

Answer 86

the lower the energy level

Question 87

atomic number

Answer 87

smaller number
number of protons
number at the bottom

Question 88

atomic mass

Answer 88

larger number

number of p and n