P4 Atomic Structure Flashcards
1
Q
Give an approximation for the radius of an atom.
A
1x10^-10 metres
2
Q
What are the three subatomic constituents of an atom?
A
- Proton
- Neutron
- Electron
3
Q
Where is most of the mass of an atom concentrated?
A
In the nucleus.
4
Q
Approximately what proportion of the total radius of an atom is the radius of the nucleus?
A
1/10,000
5
Q
Describe the arrangement of protons, neutrons and electrons in an atom.
A
- The protons and neutrons are found in the atom’s nucleus
- The electrons are found in discrete energy levels around the nucleus
6
Q
What type of charge does the nucleus of an atom have? Why?
A
- Positive charge
- The nucleus contains protons and neutrons
- Protons have a positive charge
- Neutrons have no charge
7
Q
Give two ways that an atom’s electron arrangement can be changed.
A
- Absorbing electromagnetic radiation
- Emitting electromagnetic radiation
8
Q
Explain how an atom’s electron arrangement changes when ti emits EM radiation.
A
- Electrons move closer to the nucleus
- They move to a lower energy level
8
Q
Explain how an atom’s electron arrangement changes when it absorbs EM radiation.
A
- Electrons move further away from the nucleus
- They move to a higher energy level
9
Q
How does the ratio of electrons to protons in an atom result in the atom having no overall charge?
A
- The number of protons is equal to the number of electrons
- Protons and electrons have equal and opposite charges, so charge cancels
10
Q
What do all forms of the same element have in common?
A
They all have the same number of protons.
11
Q
What is the name given to the number of protons in an atom?
A
Atomic Number
12
Q
What is an atom’s mass number?
A
The total number of protons and neutrons in the atom.
13
Q
What is an isotope of an atom?
A
An atom of an element that has a different number of neutrons, but the same number of protons.
14
Q
How do atoms turn into positive ions?
A
- They lose one or more of their outer electrons
- Electrons are negatively charged, so the resultant charge of the atom is positive
15
Q
What may lead to a scientific model being changed or replaced?
A
The discovery of new experimental evidence which doesn’t agree with the existing theory.
16
Q
How did the plum-pudding model describe the atom?
A
A ball of positive charge, with negatively charged electrons distributed evenly throughout it.
17
Q
Prior to the discovery of the electron, what was believed about the atom?
A
The atom was believed to be indivisible.
18
Q
Which experiment led ot the plum-pudding model being discarded?
A
Rutherford’s alpha-scattering experiment.
19
Q
What is the name given ot the currently accepted model of the atom?
A
The Bohr nuclear model.
20
Q
State the conclusions of the Alpha-Scattering experiment.
A
- Most of the mass of the atom is concentrated at the centre in the
nucleus - The nucleus is positively charged
21
Q
What reinforces a scientific theory?
A
When experimental results agree with the hypothesised theoretical calculations and theories
22
Q
Why do unstable nuclei give out radiation?
A
- Unstable nuclei undergo decay to become more stable
- As they release radiation their stability increases
23
Q
What did James Chadwick’s experiments on the atom prove?
A
The existence of neutrons.
24
What is the name of the process in which an unstable nucleus gives out radiation to become more stable?
Radioactive decay.
25
Define the activity of an unstable nucleus.
Activity is the rate of decay of a source of unstable nuclei.
26
What is the unit of radioactive activity?
Becquerel (Bq)
27
State four types of nuclear radiation.
1. Alpha particles
2. Beta particles
3. Gamma rays
4. Neutrons
28
What is count-rate?
The number of radioactive decays per second for a radioactive source.
29
Give an example of a detector that may be used to measure count-rate.
Geiger-Muller tube
30
What are the constituents of an alpha particle?
* Two protons and two neutrons
* It is the same as a helium nucleus
31
What is the range of an alpha particle through air?
A few centimetres (normally in the range of 2-10cm).
32
What will stop gamma radiation from passing through a point?
* Several centimetres of lead
* A few metres of concrete
32
What will stop beta radiation from passing through a point?
* A thin sheet of aluminium
* Several metres of air
33
Which type of radiation is most ionising?
Alpha radiation.
33
State any changes to mass or charge that occur due to the emission of a gamma ray.
Both mass and charge remain unchanged.
34
Which type of radiation is least ionising?
Gamma radiation.
35
Describe the nature of radioactive decay.
* Random
* Which nuclei decays and when is
determined only by chance
* It is impossible to predict which nuclei will decay and when
36
Define the half-life of a radioactive isotope.
* 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
37
What is radioactive contamination?
The presence of unwanted radioactive nuclei on other materials.
38
What is irradiation?
* The process of exposing a material to nuclear radiation
* The material does not become radioactive
39
Why is it important for the results of studies on the effects of radiation to be published and shared with other scientists?
* To allow the findings to be independently checked
* This is known as peer review
40
Give 4 sources of background radiation.
1. Rocks
2. Cosmic rays from space
3. Nuclear weapon testing
4. Nuclear accidents
41
How should background radiation be dealt with in calculations?
The background count should be subtracted from any readings before calculations (half life etc.) are attempted.
42
What is the unit used to measure radiation dosage?
Sieverts (Sv).
43
How many millisieverts equal 1sievert?
1000 millisieverts = 1 sievert
44
Why might the radiation dosage that different people experience differ?
* Some occupations involve working with radiation
* Background radiation differs with location due to things such as the locality of nuclear power stations or radiation related testing
45
What factor determines how dangerous a particular radioactive isotope is?
The half-life of the isotope.
46
Why are isotopes with long half-lives particularly harmful?
* They remain radioactive for much longer periods of time
* They must be stored in specific ways to avoid humans and the environment from
47
State two uses of nuclear radiation in the field of medicine.
1. Examining of internal organs
2. Controlling and destroying unwanted tissue
48
How is radiation used in sterilisation?
Gamma emitters are used to kill bacteria/parasites on equipment.
49
Explain the process of radiotherapy.
* Gamma emitters direct gamma rays at the cancerous cells
* The cancerous cells absorb the radiation and are killed
50
How are medical tracers chosen?
They should have a short half life and decay into a stable isotope which can be excreted.
They should only release gamma radiation since to is weakly ionising and can easily pass through body tissue without damaging it.
51
What is nuclear fission?
The splitting of large, unstable nuclei to form smaller more stable nuclei (+the emission of spare neutrons).
52
What usually needs to happen to induce fission?
* The unstable nuclei must absorb a neutron
* Spontaneous fission (where no neutron absorption occurs) is rare
52
Give an example of a fissionable isotope.
Uranium - 235
53
Alongside two smaller nuclei, what else is emitted in a fission reaction?
* Two or three neutrons
* Gamma rays
* Energy
54
What form of energy do all fission products have?
Kinetic energy.
55
What takes place during a chain reaction in a nuclear reactor?
* An unstable nucleus absorbs a neutron
* The nucleus undergoes fission and
releases 2 or 3 further neutrons
* These induce more fission, which results in a chain reaction
56
What is the consequence of an uncontrolled chain reaction?
* The rate of fission events becomes to high and results in the production of too much energy
* This can lead to a nuclear explosion
57
What are the three main components of the core a nuclear reactor?
1. Fuel rods
2. Control rods
3. Moderator
58
What is the role of the moderator ni a nuclear reactor?
To slow down the neutrons so they are travelling at speeds which allow them to be absorbed by fissile nuclei and cause fission.
59
How is the chain reaction in a fission reactor kept under control?
* Control rods are positioned in between the fuel rods
* The rate of fission is controlled by moving these rods up and down
* The lower the rods are inserted, the lower the rate of fission
60
What term is used to describe nuclei in which fission can be induced through the absorption of slow neutrons?
Fissile Nuclei
61
What is nuclear fusion?
The joining of two light nuclei to produce a heavier nuclei and release energy.
62
Name two isotopes of hydrogen which are commonly used in nuclear fusion.
Deuterium and Tritium
63
Which releases more energy, nuclear fission or nuclear fusion?
Nuclear fusion.
64
Explain the difficulty of generating energy through nuclear fusion.
Fusion requires very high temperatures which in itself requires large quantities of energy and also requires casing which can withstand them.
65
Explain why nuclear fusion is currently not a viable way to produce energy on Earth.
With current equipment/techniques, the energy required is greater than the energy produced, resulting in a net energy loss.
66
Activity:
The rate at which an unstable nucleus decays.
67
Alpha Particle:
A positively charged particle consisting of two protons and two
neutrons.
68
Atomic Number:
The number of protons found in an atom of a specific element. Each element has a different atomic number.
69
Becquerel:
The unit of radioactive activity.
70
Beta Particle:
A high speed electron that a nucleus emits when a neutron
converts into a proton.
71
Bohr Model:
A model of the atom that suggested that electrons orbit the nucleus at set distances.
72
Electrons:
A negatively charged constituent of the atom, that are found in
different energy levels, around the nucleus.
73
Count-Rate:
The number of decays that a detector measures per second.
74
Energy Levels:
The stable states in which electrons are found in around a nucleus. Electrons can transition to a higher energy level through the absorption of electromagnetic radiation and can transition to a lower energy level through the emission of electromagnetic radiation.
75
Gamma Ray:
Electromagnetic radiation emitted from a nucleus.
76
Geiger-Muller Tube:
A detector that measures the count-rate of a radioactive
sample.
77
Half-Life:
The time it takes for the number of unstable nuclei of an isotope in a sample to halve, or the time it takes for the initial count rate of a sample of the isotope to halve.
78
Ions:
Atoms with a resultant charge due to the loss or gain of electrons.
79
Irradiation:
The process of an object being exposed to nuclear radiation. The
object doesn’t become radioactive.
80
Isotopes:
Atoms with the same number of protons but different numbers of neutrons. The atomic number is the same, but the mass number is different.
81
Mass Number:
The number of protons and neutrons in an atom.
82
Negative Ions:
Atoms that gained electrons and so have a resultant negative
charge.
83
Neutrons:
A neutrally charged constituent of the nucleus.
84
Nucleus:
The positively charged centre of an atom, containing protons and neutrons.
85
Plum Pudding Model:
An old model of the atom that represented the atom as a ball of positive charge, with negative charges distributed throughout it.
86
Positive Ions:
Atoms that have lost electrons and so have a resultant positive charge.
87
Protons:
A positively charged constituent of the nucleus.
88
Radioactive Contamination:
The unwanted presence of radioactive atoms on other materials. It is hazardous due to the decay of the contaminating atoms.
89
Radioactive Decay:
The random process involving unstable nuclei emitting radiation to become more stable.
