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Physics AQA > P4 Atomic Structure > Flashcards

P4 Atomic Structure Flashcards

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1
Q

Give an approximation for the radius of an atom.

A

1x10^-10 metres

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2
Q

What are the three subatomic constituents of an atom?

A
  1. Proton
  2. Neutron
  3. Electron
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3
Q

Where is most of the mass of an atom concentrated?

A

In the nucleus.

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4
Q

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

A

1/10,000

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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
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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
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7
Q

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

A
  1. Absorbing electromagnetic radiation
  2. Emitting electromagnetic radiation
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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
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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
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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
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10
Q

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

A

They all have the same number of protons.

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11
Q

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

A

Atomic Number

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12
Q

What is an atom’s mass number?

A

The total number of protons and neutrons in the atom.

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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.

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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
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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.

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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.

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17
Q

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

A

The atom was believed to be indivisible.

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18
Q

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

A

Rutherford’s alpha-scattering experiment.

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19
Q

What is the name given ot the currently accepted model of the atom?

A

The Bohr nuclear model.

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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
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21
Q

What reinforces a scientific theory?

A

When experimental results agree with the hypothesised theoretical calculations and theories

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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
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23
Q

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

A

The existence of neutrons.

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24
Q

What is the name of the process in which an unstable nucleus gives out radiation to become more stable?

A

Radioactive decay.

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25
Q

Define the activity of an unstable nucleus.

A

Activity is the rate of decay of a source of unstable nuclei.

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26
Q

What is the unit of radioactive activity?

A

Becquerel (Bq)

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27
Q

State four types of nuclear radiation.

A
  1. Alpha particles
  2. Beta particles
  3. Gamma rays
  4. Neutrons
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28
Q

What is count-rate?

A

The number of radioactive decays per second for a radioactive source.

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29
Q

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

A

Geiger-Muller tube

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30
Q

What are the constituents of an alpha particle?

A
  • Two protons and two neutrons
  • It is the same as a helium nucleus
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31
Q

What is the range of an alpha particle through air?

A

A few centimetres (normally in the range of 2-10cm).

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32
Q

What will stop gamma radiation from passing through a point?

A
  • Several centimetres of lead
  • A few metres of concrete
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32
Q

What will stop beta radiation from passing through a point?

A
  • A thin sheet of aluminium
  • Several metres of air
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33
Q

Which type of radiation is most ionising?

A

Alpha radiation.

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33
Q

State any changes to mass or charge that occur due to the emission of a gamma ray.

A

Both mass and charge remain unchanged.

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34
Q

Which type of radiation is least ionising?

A

Gamma radiation.

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35
Q

Describe the nature of radioactive decay.

A
  • Random
  • Which nuclei decays and when is
    determined only by chance
  • It is impossible to predict which nuclei will decay and when
36
Q

Define the half-life of a radioactive isotope.

A
  • 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
Q

What is radioactive contamination?

A

The presence of unwanted radioactive nuclei on other materials.

38
Q

What is irradiation?

A
  • The process of exposing a material to nuclear radiation
  • The material does not become radioactive
39
Q

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

A
  • To allow the findings to be independently checked
  • This is known as peer review
40
Q

Give 4 sources of background radiation.

A
  1. Rocks
  2. Cosmic rays from space
  3. Nuclear weapon testing
  4. Nuclear accidents
41
Q

How should background radiation be dealt with in calculations?

A

The background count should be subtracted from any readings before calculations (half life etc.) are attempted.

42
Q

What is the unit used to measure radiation dosage?

A

Sieverts (Sv).

43
Q

How many millisieverts equal 1sievert?

A

1000 millisieverts = 1 sievert

44
Q

Why might the radiation dosage that different people experience differ?

A
  • 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
Q

What factor determines how dangerous a particular radioactive isotope is?

A

The half-life of the isotope.

46
Q

Why are isotopes with long half-lives particularly harmful?

A
  • They remain radioactive for much longer periods of time
  • They must be stored in specific ways to avoid humans and the environment from
47
Q

State two uses of nuclear radiation in the field of medicine.

A
  1. Examining of internal organs
  2. Controlling and destroying unwanted tissue
48
Q

How is radiation used in sterilisation?

A

Gamma emitters are used to kill bacteria/parasites on equipment.

49
Q

Explain the process of radiotherapy.

A
  • Gamma emitters direct gamma rays at the cancerous cells
  • The cancerous cells absorb the radiation and are killed
50
Q

How are medical tracers chosen?

A

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
Q

What is nuclear fission?

A

The splitting of large, unstable nuclei to form smaller more stable nuclei (+the emission of spare neutrons).

52
Q

What usually needs to happen to induce fission?

A
  • The unstable nuclei must absorb a neutron
  • Spontaneous fission (where no neutron absorption occurs) is rare
52
Q

Give an example of a fissionable isotope.

A

Uranium - 235

53
Q

Alongside two smaller nuclei, what else is emitted in a fission reaction?

A
  • Two or three neutrons
  • Gamma rays
  • Energy
54
Q

What form of energy do all fission products have?

A

Kinetic energy.

55
Q

What takes place during a chain reaction in a nuclear reactor?

A
  • 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
Q

What is the consequence of an uncontrolled chain reaction?

A
  • 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
Q

What are the three main components of the core a nuclear reactor?

A
  1. Fuel rods
  2. Control rods
  3. Moderator
58
Q

What is the role of the moderator ni a nuclear reactor?

A

To slow down the neutrons so they are travelling at speeds which allow them to be absorbed by fissile nuclei and cause fission.

59
Q

How is the chain reaction in a fission reactor kept under control?

A
  • 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
Q

What term is used to describe nuclei in which fission can be induced through the absorption of slow neutrons?

A

Fissile Nuclei

61
Q

What is nuclear fusion?

A

The joining of two light nuclei to produce a heavier nuclei and release energy.

62
Q

Name two isotopes of hydrogen which are commonly used in nuclear fusion.

A

Deuterium and Tritium

63
Q

Which releases more energy, nuclear fission or nuclear fusion?

A

Nuclear fusion.

64
Q

Explain the difficulty of generating energy through nuclear fusion.

A

Fusion requires very high temperatures which in itself requires large quantities of energy and also requires casing which can withstand them.

65
Q

Explain why nuclear fusion is currently not a viable way to produce energy on Earth.

A

With current equipment/techniques, the energy required is greater than the energy produced, resulting in a net energy loss.

66
Q

Activity:

A

The rate at which an unstable nucleus decays.

67
Q

Alpha Particle:​

A

A positively charged particle consisting of two protons and two
neutrons.

68
Q

Atomic Number:​

A

The number of protons found in an atom of a specific element. Each element has a different atomic number.

69
Q

Becquerel:​

A

The unit of radioactive activity.

70
Q

Beta Particle:​

A

A high speed electron that a nucleus emits when a neutron
converts into a proton.

71
Q

Bohr Model:

A

A model of the atom that suggested that electrons orbit the nucleus at set distances.

72
Q

Electrons:

A

​A negatively charged constituent of the atom, that are found in
different energy levels, around the nucleus.

73
Q

Count-Rate:​

A

The number of decays that a detector measures per second.

74
Q

Energy Levels:​

A

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
Q

Gamma Ray:​

A

Electromagnetic radiation emitted from a nucleus.

76
Q

Geiger-Muller Tube:​

A

A detector that measures the count-rate of a radioactive
sample.

77
Q

Half-Life:​

A

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
Q

Ions:​

A

Atoms with a resultant charge due to the loss or gain of electrons.

79
Q

Irradiation:​

A

The process of an object being exposed to nuclear radiation. The
object doesn’t become radioactive.

80
Q

Isotopes:​

A

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
Q

Mass Number:​

A

The number of protons and neutrons in an atom.

82
Q

Negative Ions:

A

Atoms that gained electrons and so have a resultant negative
charge.

83
Q

Neutrons:

A

A neutrally charged constituent of the nucleus.

84
Q

Nucleus:

A

The positively charged centre of an atom, containing protons and neutrons.

85
Q

Plum Pudding Model:

A

An old model of the atom that represented the atom as a ball of positive charge, with negative charges distributed throughout it.

86
Q

Positive Ions:

A

Atoms that have lost electrons and so have a resultant positive charge.

87
Q

Protons:​

A

A positively charged constituent of the nucleus.

88
Q

Radioactive Contamination:​

A

The unwanted presence of radioactive atoms on other materials. It is hazardous due to the decay of the contaminating atoms.

89
Q

Radioactive Decay:

A

The random process involving unstable nuclei emitting radiation to become more stable.

Physics AQA (4 decks)

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