P4- Atomic structure Flashcards
1
Q
When did Democtrius come up with the idea of the atom
A
5th century BC
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)
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.
4
Q
What happened in 1909 that changed the idea of the atom
A
The gold foil experiment.
5
Q
What was the gold foil experiment
A
They fired a beam of alpha particles at thin gold foil.
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
7
Q
Who was in charge of the gold foil experiment
A
Rutherford
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
9
Q
Where did the gold foil experiment prove most of the mass was
A
In the nucleus
10
Q
What charge did the gold foil experiment show the nucleus having
A
Positive
11
Q
What model came out of the gold foil experiment
A
Nuclear
12
Q
Describe the nucleus model
A
Positively charged nucleus surrounded by a cloud of negative electrons
13
Q
Who said that electrons orbit the nucleus
A
Niels Bohr
14
Q
Who proved the existence of the neutron
A
James Chadwick
15
Q
When was the neutron discovered
A
1932
16
Q
What is an isotope
A
An atom with the same number of protons but a different number of neutrons
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
18
Q
What does losing radiation do
A
Creats positive ions
19
Q
What is an alpha particle
A
Helium nuclei
20
Q
When does alpha radiation happen
A
When an alpha particle is emitted from the nucleus.
21
Q
How many neutrons and protons does and alpha particle have
A
2 of each
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
23
Q
Is alpha weakly ionising
A
because of its size it’s strongly ionising
24
Q
What is beta
A
High-speed electrons released by the nucleus
25
What is the mass if beta
virtually 0
26
What is the charge of beta
-1
27
Are beta weakly ionising
Beta is moderately ionising
28
How far does alpha travel
a few cm in air and are absorbed by a sheet of paper
29
How far does beta penetrate
moderately far, a few meters
30
What happens to a neutron when a beta particle is emitted
A neutron in the nucleus has turned into a proton
31
What is a gamma wave
Waves of electromagnetic radiation released by the nucleus
32
Does gamma penetrate far into materials
Gamma penetrates far into materials
33
Does gamma travel long distances in the air
Gamma does travel long distances in the air
34
Is gamma a weak ionising
Gamma weakly ionises
35
What are the materials that absorb gamma
- Lead
| - (meters of )Concrete
36
What do nuclear equations show
Radioactive decay
37
What is the mass number for alpha
4
38
What is the atomic number for alpha
2
39
In an equation alpha particles can be written as a _ nucleus
Helium
40
What is the mass number for beta
0
41
What is the atomic number for beta
-1
42
With beta radiation what's released
A fast moving electron
43
Why doesn't gamma have a charge or mass
It's a wave
44
What happens to the radioactivity to a source over time
It decreases
45
What does a substance become when it radioactively decays
It becomes a stable nucleus
46
Define half-life
The time taken for the number of radioactive nuclei is an isotope to halve
47
What is background radiation
The low-level radiation that's around us all the time
48
What is radiation from space known as
Cosmic rays
49
What's radiation measured in
sieverts
50
What is exposure to radiation called
Irradiation
51
What are the risks to using radiation
- 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
52
When are gamma sources usually used
In medical tracers
53
How can radiation help cure cancer
Radiothereapy
54
What is nucleon fission
A type of nuclear reaction that is used to release energy from large and unstable atoms by splitting them into smaller atoms
55
Can spontaneous fission happen
Yes, but rarely
56
What do atoms form when they split
- 2 new lighter elements that are roughly the same size
| - 2 or 3 neutrons
57
During nuclear fission what happens to the energy that is not transferred into kinetic energy
It's carried away by gamma rays
58
How do nuclear weapons work
Uncontrolled chain reactions quickly lead to lots of energy being released as an explosion
59
What is nuclear fusion
Two light nuclei collide at high speed and join (fuse) to create a larger, heavier nucleus
60
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
True
61
Explain how the resistance changes as the potential difference
across it increases.
```
the current increases (when the
potential difference increases)
(which) causes the temperature
of the filament to increase
(so) the resistance increases
```
62
What is the name of one fuel used in nuclear power stations?
uranium
or
plutonium
63
State two environmental issues caused by generating electricity using nuclear
power stations.
```
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
Give an approximation for the radius of an atom.
1x10⁻¹⁰ metres
65
What are the three subatomic
| constituents of an atom?
1. Proton
2. Neutron
3. Electron
66
Where is most of the mass of an atom
| concentrated?
In the nucleus.
67
Approximately what proportion of the
total radius of an atom is the radius of
the nucleus?
1/10,000
68
Describe the arrangement of protons,
| neutrons and electrons in an atom.
● The protons and neutrons are found in
the atom’s nucleus
● The electrons are found in discrete
energy levels around the nucleus
69
What type of charge does the nucleus of
| an atom have? Why?
● Positive charge
● The nucleus contains protons and neutrons
● Protons have a positive charge
● Neutrons have no charge
70
Give two ways that an atom’s electron
| arrangement can be changed.
1. Absorbing electromagnetic radiation
| 2. Emitting electromagnetic radiation
71
Explain how an atom’s electron
arrangement changes when it absorbs
EM radiation.
● Electrons move further away from the
nucleus
● They move to a higher energy level
72
Explain how an atom’s electron
arrangement changes when it emits EM
radiation.
● Electrons move closer to the nucleus
| ● They move to a lower energy level
73
How does the ratio of electrons to protons in an atom
| result in the atom having no overall charge?
● The number of protons is equal to the
number of electrons
● Protons and electrons have equal and
opposite charges, so charge cancels
74
What do all forms of the same element
| have in common?
They all have the same number of
| protons.
75
What is the name given to the number of
| protons in an atom?
Atomic Number
76
What is an atom’s mass number?
The total number of protons and
| neutrons in the atom.
77
What is an isotope of an atom?
An atom of an element that has a
different number of neutrons, but the
same number of protons.
78
How do atoms turn into positive ions?
```
● They lose one or more of their outer
electrons
● Electrons are negatively charged, so
the resultant charge of the atom is
positive
```
79
What may lead to a scientific model being changed
| or replaced?
A ball of positive charge, with negatively
charged electrons distributed evenly
throughout it.
80
Prior to the discovery of the electron, what was
| believed about the atom?
The atom was believed to be indivisible
81
Which experiment led to the plum-pudding model
| being discarded?
Rutherford’s alpha-scattering
| experiment.
82
What is the name given to the currently
| accepted model of the atom?
The Bohr nuclear model.
83
State the conclusions of the Alpha-Scattering
| experiment.
● Most of the mass of the atom is
concentrated at the centre in the
nucleus
● The nucleus is positively charged
84
What reinforces a scientific theory?
When experimental results agree with
the hypothesised theoretical calculations
and theories.
85
What did James Chadwick’s experiments on the
| atom prove?
The existence of neutrons.
86
Why do unstable nuclei give out
| radiation?
● Unstable nuclei undergo decay to
become more stable
● As they release radiation their stability
increases
87
What is the name of the process in which
an unstable nucleus gives out radiation
to become more stable?
Radioactive decay.
88
Define the activity of an unstable
| nucleus.
Activity is the rate of decay of a source of
| unstable nuclei.
89
What is the unit of radioactive activity?
Becquerel (Bq)
90
What is count-rate?
The number of radioactive decays per
| second for a radioactive source.
91
Give an example of a detector that may be used to
| measure count-rate.
Geiger-Muller tube
92
State four types of nuclear radiation.
1. Alpha particles
2. Beta particles
3. Gamma rays
4. Neutrons
93
What are the constituents of an alpha particle?
● Two protons and two neutrons
| ● It is the same as a helium nucleus
94
What is the range of an alpha particle
| through air?
A few centimetres (normally in the range
| of 2-10cm).
95
What will stop beta radiation from
| passing through a point?
● A thin sheet of aluminium
| ● Several metres of air
96
What will stop gamma radiation from passing
| through a point?
● Several centimetres of lead
| ● A few metres of concrete
97
Which type of radiation is most ionising?
Alpha radiation.
98
Which type of radiation is least ionising?
Gamma radiation.
99
State any changes to mass or charge
that occur due to the emission of a
gamma ray.
Both mass and charge remain
| unchanged.
100
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
```
101
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
```
102
What is radioactive contamination?
The presence of unwanted radioactive
| nuclei on other materials.
103
What is irradiation?
● The process of exposing a material to
nuclear radiation
● The material does not become
radioactive
104
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
105
Give 4 sources of background radiation.
1. Rocks
2. Cosmic rays from space
3. Nuclear weapon testing
4. Nuclear accidents
106
How should background radiation be dealt with in
| calculations?
The background count should be
subtracted from any readings before
calculations (half life etc.) are attempte
107
What is the unit used to measure radiation dosage?
Sieverts (Sv).
108
How many millisieverts equal 1 sievert?
1000 millisieverts = 1 sievert
109
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
110
What factor determines how dangerous
| a particular radioactive isotope is?
The half-life of the isotope.
111
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
being exposed to radiation for too long
112
State two uses of nuclear radiation in the field of
| medicine.
1. Examining of internal organs
2. Controlling and destroying unwanted
tissue
113
How is radiation used in sterilisation?
Gamma emitters are used to kill
| bacteria/parasites on equipment.
114
Explain the process of radiotherapy.
● Gamma emitters direct gamma rays at
the cancerous cells
● The cancerous cells absorb the
radiation and are killed
115
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
it is weakly ionising and can easily pass through
body tissue without damaging it.
116
What is nuclear fission?
The splitting of large, unstable nuclei to
form smaller more stable nuclei (+the
emission of spare neutrons).
117
Give an example of a fissionable isotope.
Uranium - 235
118
What usually needs to happen to induce fission?
● The unstable nuclei must absorb a
neutron
● Spontaneous fission (where no
neutron absorption occurs) is rare
119
Alongside two smaller nuclei, what else
| is emitted in a fission reaction?
● Two or three neutrons
● Gamma rays
● Energy
120
What form of energy do all fission products have?
Kinetic energy.
121
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
```
122
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
123
What are the three main components of
| the core a nuclear reactor?
1. Fuel rods
2. Control rods
3. Moderator
124
What is the role of the moderator in 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.
125
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 slower the
rate of fission
126
What term is used to describe nuclei in which fission
can be induced through the absorption of slow
neutrons?
Fissile Nuclei
127
What is nuclear fusion?
The joining of two light nuclei to produce
| a heavier nuclei and release energy.
128
Name two isotopes of hydrogen which
| are commonly used in nuclear fusion.
Deuterium and Tritium
129
Which releases more energy, nuclear
| fission or nuclear fusion?
Nuclear fusion.
130
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.
131
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.
