Unit 4 - The Atom & Decay Flashcards
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
- 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?
The discovery of new experimental
evidence which doesn’t agree with the
existing theory.
How did the plum-pudding model describe the atom?
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
