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Physics > P4- Atomic structure > Flashcards

P4- Atomic structure Flashcards

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1
Q

When did Democtrius come up with the idea of the atom

A

5th century BC

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2
Q

What did John Dalton do regarding the discovery of the atom

A

He agreed with Democtritus that matter was made of tiny spheres that couldn’t be broken up,but he reckoned that each element was made up of a different type of atom(1804)

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3
Q

What did J.J Thomson do regarding the discovery of the atom

A

He discovered particles called electrons that could be removed from atoms. He suggested that atoms were spheres of positive charge with tiny negative electrons stuck in them like fruit in a plum pudding model.

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4
Q

What happened in 1909 that changed the idea of the atom

A

The gold foil experiment.

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5
Q

What was the gold foil experiment

A

They fired a beam of alpha particles at thin gold foil.

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6
Q

What did they expect to happen with the gold foil experiment

A

The particles to go straight through the sheet or be slightly defected

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7
Q

Who was in charge of the gold foil experiment

A

Rutherford

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8
Q

What actually happened in the gold foil experiment

A

Most of the particles went straight through,some where deflected but more than expected, a few were deflected back

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9
Q

Where did the gold foil experiment prove most of the mass was

A

In the nucleus

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10
Q

What charge did the gold foil experiment show the nucleus having

A

Positive

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11
Q

What model came out of the gold foil experiment

A

Nuclear

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12
Q

Describe the nucleus model

A

Positively charged nucleus surrounded by a cloud of negative electrons

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13
Q

Who said that electrons orbit the nucleus

A

Niels Bohr

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14
Q

Who proved the existence of the neutron

A

James Chadwick

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15
Q

When was the neutron discovered

A

1932

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16
Q

What is an isotope

A

An atom with the same number of protons but a different number of neutrons

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17
Q

What is radioactive decay

A

When unstable isotopes tend to decay into other elements and give out radiation as they try to become more stabel

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18
Q

What does losing radiation do

A

Creats positive ions

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19
Q

What is an alpha particle

A

Helium nuclei

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20
Q

When does alpha radiation happen

A

When an alpha particle is emitted from the nucleus.

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21
Q

How many neutrons and protons does and alpha particle have

A

2 of each

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22
Q

Explain how alpha particles are used in smoke detectors

A

It ionises air particles, causing a current to flow. If there is smoke in the air, it binds to the ions-meaning the current stops the smoke alarm

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23
Q

Is alpha weakly ionising

A

because of its size it’s strongly ionising

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24
Q

What is beta

A

High-speed electrons released by the nucleus

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25
Q

What is the mass if beta

A

virtually 0

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26
Q

What is the charge of beta

A

-1

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27
Q

Are beta weakly ionising

A

Beta is moderately ionising

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28
Q

How far does alpha travel

A

a few cm in air and are absorbed by a sheet of paper

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29
Q

How far does beta penetrate

A

moderately far, a few meters

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30
Q

What happens to a neutron when a beta particle is emitted

A

A neutron in the nucleus has turned into a proton

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31
Q

What is a gamma wave

A

Waves of electromagnetic radiation released by the nucleus

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32
Q

Does gamma penetrate far into materials

A

Gamma penetrates far into materials

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33
Q

Does gamma travel long distances in the air

A

Gamma does travel long distances in the air

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34
Q

Is gamma a weak ionising

A

Gamma weakly ionises

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35
Q

What are the materials that absorb gamma

A
  • Lead

- (meters of )Concrete

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36
Q

What do nuclear equations show

A

Radioactive decay

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37
Q

What is the mass number for alpha

A

4

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38
Q

What is the atomic number for alpha

A

2

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39
Q

In an equation alpha particles can be written as a _ nucleus

A

Helium

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40
Q

What is the mass number for beta

A

0

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41
Q

What is the atomic number for beta

A

-1

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42
Q

With beta radiation what’s released

A

A fast moving electron

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43
Q

Why doesn’t gamma have a charge or mass

A

It’s a wave

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44
Q

What happens to the radioactivity to a source over time

A

It decreases

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45
Q

What does a substance become when it radioactively decays

A

It becomes a stable nucleus

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46
Q

Define half-life

A

The time taken for the number of radioactive nuclei is an isotope to halve

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47
Q

What is background radiation

A

The low-level radiation that’s around us all the time

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48
Q

What is radiation from space known as

A

Cosmic rays

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49
Q

What’s radiation measured in

A

sieverts

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50
Q

What is exposure to radiation called

A

Irradiation

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51
Q

What are the risks to using radiation

A
  • It can enter living cells and ionise atoms and molecules within them. This can lead to tissue damage
  • Lower doses tend to cause minor damage without killing the cells. This can give rise to mutant cells which divide uncontrollably
  • Higher doses tend to kill cells completely, causing radiation sickness (leading to vomiting, tiredness and hair loss) if a lot of cells all get batted at once
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52
Q

When are gamma sources usually used

A

In medical tracers

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53
Q

How can radiation help cure cancer

A

Radiothereapy

54
Q

What is nucleon fission

A

A type of nuclear reaction that is used to release energy from large and unstable atoms by splitting them into smaller atoms

55
Q

Can spontaneous fission happen

A

Yes, but rarely

56
Q

What do atoms form when they split

A
  • 2 new lighter elements that are roughly the same size

- 2 or 3 neutrons

57
Q

During nuclear fission what happens to the energy that is not transferred into kinetic energy

A

It’s carried away by gamma rays

58
Q

How do nuclear weapons work

A

Uncontrolled chain reactions quickly lead to lots of energy being released as an explosion

59
Q

What is nuclear fusion

A

Two light nuclei collide at high speed and join (fuse) to create a larger, heavier nucleus

60
Q

True/ False
The heavier nucleus produces by fusion doesn’t have as much mass as the two separate, light nuclei did. Some of the mass of the lighter nuclei is converted to energy. This is then released as radiation

A

True

61
Q

Explain how the resistance changes as the potential difference
across it increases.

A 
the current increases (when the
potential difference increases)
(which) causes the temperature
of the filament to increase
(so) the resistance increases
62
Q

What is the name of one fuel used in nuclear power stations?

A

uranium
or
plutonium

63
Q

State two environmental issues caused by generating electricity using nuclear
power stations.

A 
any two from:
• waste is radioactive
• waste has a long half-life
• waste is toxic
• waste needs to be buried
• risk of catastrophic
accidents
• fuel is non-renewable
64
Q

Give an approximation for the radius of an atom.

A

1x10⁻¹⁰ metres

65
Q

What are the three subatomic

constituents of an atom?

A
  1. Proton
  2. Neutron
  3. Electron
66
Q

Where is most of the mass of an atom

concentrated?

A

In the nucleus.

67
Q

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

A

1/10,000

68
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

69
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

70
Q

Give two ways that an atom’s electron

arrangement can be changed.

A
  1. Absorbing electromagnetic radiation

2. Emitting electromagnetic radiation

71
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

72
Q

Explain how an atom’s electron
arrangement changes when it emits EM
radiation.

A

● Electrons move closer to the nucleus

● They move to a lower energy level

73
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

74
Q

What do all forms of the same element

have in common?

A

They all have the same number of

protons.

75
Q

What is the name given to the number of

protons in an atom?

A

Atomic Number

76
Q

What is an atom’s mass number?

A

The total number of protons and

neutrons in the atom.

77
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.

78
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
79
Q

What may lead to a scientific model being changed

or replaced?

A

A ball of positive charge, with negatively
charged electrons distributed evenly
throughout it.

80
Q

Prior to the discovery of the electron, what was

believed about the atom?

A

The atom was believed to be indivisible

81
Q

Which experiment led to the plum-pudding model

being discarded?

A

Rutherford’s alpha-scattering

experiment.

82
Q

What is the name given to the currently

accepted model of the atom?

A

The Bohr nuclear model.

83
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

84
Q

What reinforces a scientific theory?

A

When experimental results agree with
the hypothesised theoretical calculations
and theories.

85
Q

What did James Chadwick’s experiments on the

atom prove?

A

The existence of neutrons.

86
Q

Why do unstable nuclei give out

radiation?

A

● Unstable nuclei undergo decay to
become more stable
● As they release radiation their stability
increases

87
Q

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

A

Radioactive decay.

88
Q

Define the activity of an unstable

nucleus.

A

Activity is the rate of decay of a source of

unstable nuclei.

89
Q

What is the unit of radioactive activity?

A

Becquerel (Bq)

90
Q

What is count-rate?

A

The number of radioactive decays per

second for a radioactive source.

91
Q

Give an example of a detector that may be used to

measure count-rate.

A

Geiger-Muller tube

92
Q

State four types of nuclear radiation.

A
  1. Alpha particles
  2. Beta particles
  3. Gamma rays
  4. Neutrons
93
Q

What are the constituents of an alpha particle?

A

● Two protons and two neutrons

● It is the same as a helium nucleus

94
Q

What is the range of an alpha particle

through air?

A

A few centimetres (normally in the range

of 2-10cm).

95
Q

What will stop beta radiation from

passing through a point?

A

● A thin sheet of aluminium

● Several metres of air

96
Q

What will stop gamma radiation from passing

through a point?

A

● Several centimetres of lead

● A few metres of concrete

97
Q

Which type of radiation is most ionising?

A

Alpha radiation.

98
Q

Which type of radiation is least ionising?

A

Gamma radiation.

99
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.

100
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
101
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
102
Q

What is radioactive contamination?

A

The presence of unwanted radioactive

nuclei on other materials.

103
Q

What is irradiation?

A

● The process of exposing a material to
nuclear radiation
● The material does not become
radioactive

104
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

105
Q

Give 4 sources of background radiation.

A
  1. Rocks
  2. Cosmic rays from space
  3. Nuclear weapon testing
  4. Nuclear accidents
106
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 attempte

107
Q

What is the unit used to measure radiation dosage?

A

Sieverts (Sv).

108
Q

How many millisieverts equal 1 sievert?

A

1000 millisieverts = 1 sievert

109
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

110
Q

What factor determines how dangerous

a particular radioactive isotope is?

A

The half-life of the isotope.

111
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
being exposed to radiation for too long

112
Q

State two uses of nuclear radiation in the field of

medicine.

A
  1. Examining of internal organs
  2. Controlling and destroying unwanted
    tissue
113
Q

How is radiation used in sterilisation?

A

Gamma emitters are used to kill

bacteria/parasites on equipment.

114
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

115
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
it is weakly ionising and can easily pass through
body tissue without damaging it.

116
Q

What is nuclear fission?

A

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

117
Q

Give an example of a fissionable isotope.

A

Uranium - 235

118
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

119
Q

Alongside two smaller nuclei, what else

is emitted in a fission reaction?

A

● Two or three neutrons
● Gamma rays
● Energy

120
Q

What form of energy do all fission products have?

A

Kinetic energy.

121
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
122
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

123
Q

What are the three main components of

the core a nuclear reactor?

A
  1. Fuel rods
  2. Control rods
  3. Moderator
124
Q

What is the role of the moderator in 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.

125
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 slower the
rate of fission

126
Q

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

A

Fissile Nuclei

127
Q

What is nuclear fusion?

A

The joining of two light nuclei to produce

a heavier nuclei and release energy.

128
Q

Name two isotopes of hydrogen which

are commonly used in nuclear fusion.

A

Deuterium and Tritium

129
Q

Which releases more energy, nuclear

fission or nuclear fusion?

A

Nuclear fusion.

130
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.

131
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.

Physics (8 decks)

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