P4- Atomic structure Flashcards
When did Democtrius come up with the idea of the atom
5th century BC
What did John Dalton do regarding the discovery of the atom
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)
What did J.J Thomson do regarding the discovery of the atom
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.
What happened in 1909 that changed the idea of the atom
The gold foil experiment.
What was the gold foil experiment
They fired a beam of alpha particles at thin gold foil.
What did they expect to happen with the gold foil experiment
The particles to go straight through the sheet or be slightly defected
Who was in charge of the gold foil experiment
Rutherford
What actually happened in the gold foil experiment
Most of the particles went straight through,some where deflected but more than expected, a few were deflected back
Where did the gold foil experiment prove most of the mass was
In the nucleus
What charge did the gold foil experiment show the nucleus having
Positive
What model came out of the gold foil experiment
Nuclear
Describe the nucleus model
Positively charged nucleus surrounded by a cloud of negative electrons
Who said that electrons orbit the nucleus
Niels Bohr
Who proved the existence of the neutron
James Chadwick
When was the neutron discovered
1932
What is an isotope
An atom with the same number of protons but a different number of neutrons
What is radioactive decay
When unstable isotopes tend to decay into other elements and give out radiation as they try to become more stabel
What does losing radiation do
Creats positive ions
What is an alpha particle
Helium nuclei
When does alpha radiation happen
When an alpha particle is emitted from the nucleus.
How many neutrons and protons does and alpha particle have
2 of each
Explain how alpha particles are used in smoke detectors
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
Is alpha weakly ionising
because of its size it’s strongly ionising
What is beta
High-speed electrons released by the nucleus
What is the mass if beta
virtually 0
What is the charge of beta
-1
Are beta weakly ionising
Beta is moderately ionising
How far does alpha travel
a few cm in air and are absorbed by a sheet of paper
How far does beta penetrate
moderately far, a few meters
What happens to a neutron when a beta particle is emitted
A neutron in the nucleus has turned into a proton
What is a gamma wave
Waves of electromagnetic radiation released by the nucleus
Does gamma penetrate far into materials
Gamma penetrates far into materials
Does gamma travel long distances in the air
Gamma does travel long distances in the air
Is gamma a weak ionising
Gamma weakly ionises
What are the materials that absorb gamma
- Lead
- (meters of )Concrete
What do nuclear equations show
Radioactive decay
What is the mass number for alpha
4
What is the atomic number for alpha
2
In an equation alpha particles can be written as a _ nucleus
Helium
What is the mass number for beta
0
What is the atomic number for beta
-1
With beta radiation what’s released
A fast moving electron
Why doesn’t gamma have a charge or mass
It’s a wave
What happens to the radioactivity to a source over time
It decreases
What does a substance become when it radioactively decays
It becomes a stable nucleus
Define half-life
The time taken for the number of radioactive nuclei is an isotope to halve
What is background radiation
The low-level radiation that’s around us all the time
What is radiation from space known as
Cosmic rays
What’s radiation measured in
sieverts
What is exposure to radiation called
Irradiation
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
When are gamma sources usually used
In medical tracers
How can radiation help cure cancer
Radiothereapy
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
Can spontaneous fission happen
Yes, but rarely
What do atoms form when they split
- 2 new lighter elements that are roughly the same size
- 2 or 3 neutrons
During nuclear fission what happens to the energy that is not transferred into kinetic energy
It’s carried away by gamma rays
How do nuclear weapons work
Uncontrolled chain reactions quickly lead to lots of energy being released as an explosion
What is nuclear fusion
Two light nuclei collide at high speed and join (fuse) to create a larger, heavier nucleus
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
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
What is the name of one fuel used in nuclear power stations?
uranium
or
plutonium
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
Give an approximation for the radius of an atom.
1x10⁻¹⁰ metres
What are the three subatomic
constituents of an atom?
- Proton
- Neutron
- Electron
Where is most of the mass of an atom
concentrated?
In the nucleus.
Approximately what proportion of the
total radius of an atom is the radius of
the nucleus?
1/10,000
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
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
Give two ways that an atom’s electron
arrangement can be changed.
- Absorbing electromagnetic radiation
2. Emitting electromagnetic radiation
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
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
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
What do all forms of the same element
have in common?
They all have the same number of
protons.
What is the name given to the number of
protons in an atom?
Atomic Number
What is an atom’s mass number?
The total number of protons and
neutrons in the atom.
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.
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
What may lead to a scientific model being changed
or replaced?
A ball of positive charge, with negatively
charged electrons distributed evenly
throughout it.
Prior to the discovery of the electron, what was
believed about the atom?
The atom was believed to be indivisible
Which experiment led to the plum-pudding model
being discarded?
Rutherford’s alpha-scattering
experiment.
What is the name given to the currently
accepted model of the atom?
The Bohr nuclear model.
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
What reinforces a scientific theory?
When experimental results agree with
the hypothesised theoretical calculations
and theories.
What did James Chadwick’s experiments on the
atom prove?
The existence of neutrons.
Why do unstable nuclei give out
radiation?
● Unstable nuclei undergo decay to
become more stable
● As they release radiation their stability
increases
What is the name of the process in which
an unstable nucleus gives out radiation
to become more stable?
Radioactive decay.
Define the activity of an unstable
nucleus.
Activity is the rate of decay of a source of
unstable nuclei.
What is the unit of radioactive activity?
Becquerel (Bq)
What is count-rate?
The number of radioactive decays per
second for a radioactive source.
Give an example of a detector that may be used to
measure count-rate.
Geiger-Muller tube
State four types of nuclear radiation.
- Alpha particles
- Beta particles
- Gamma rays
- Neutrons
What are the constituents of an alpha particle?
● Two protons and two neutrons
● It is the same as a helium nucleus
What is the range of an alpha particle
through air?
A few centimetres (normally in the range
of 2-10cm).
What will stop beta radiation from
passing through a point?
● A thin sheet of aluminium
● Several metres of air
What will stop gamma radiation from passing
through a point?
● Several centimetres of lead
● A few metres of concrete
Which type of radiation is most ionising?
Alpha radiation.
Which type of radiation is least ionising?
Gamma radiation.
State any changes to mass or charge
that occur due to the emission of a
gamma ray.
Both mass and charge remain
unchanged.
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
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
What is radioactive contamination?
The presence of unwanted radioactive
nuclei on other materials.
What is irradiation?
● The process of exposing a material to
nuclear radiation
● The material does not become
radioactive
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
Give 4 sources of background radiation.
- Rocks
- Cosmic rays from space
- Nuclear weapon testing
- Nuclear accidents
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
What is the unit used to measure radiation dosage?
Sieverts (Sv).
How many millisieverts equal 1 sievert?
1000 millisieverts = 1 sievert
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
What factor determines how dangerous
a particular radioactive isotope is?
The half-life of the isotope.
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
State two uses of nuclear radiation in the field of
medicine.
- Examining of internal organs
- Controlling and destroying unwanted
tissue
How is radiation used in sterilisation?
Gamma emitters are used to kill
bacteria/parasites on equipment.
Explain the process of radiotherapy.
● Gamma emitters direct gamma rays at
the cancerous cells
● The cancerous cells absorb the
radiation and are killed
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.
What is nuclear fission?
The splitting of large, unstable nuclei to
form smaller more stable nuclei (+the
emission of spare neutrons).
Give an example of a fissionable isotope.
Uranium - 235
What usually needs to happen to induce fission?
● The unstable nuclei must absorb a
neutron
● Spontaneous fission (where no
neutron absorption occurs) is rare
Alongside two smaller nuclei, what else
is emitted in a fission reaction?
● Two or three neutrons
● Gamma rays
● Energy
What form of energy do all fission products have?
Kinetic energy.
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
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
What are the three main components of
the core a nuclear reactor?
- Fuel rods
- Control rods
- Moderator
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.
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
What term is used to describe nuclei in which fission
can be induced through the absorption of slow
neutrons?
Fissile Nuclei
What is nuclear fusion?
The joining of two light nuclei to produce
a heavier nuclei and release energy.
Name two isotopes of hydrogen which
are commonly used in nuclear fusion.
Deuterium and Tritium
Which releases more energy, nuclear
fission or nuclear fusion?
Nuclear fusion.
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.
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.
