Download Candidate 2 - Elgin Academy

The following is an extract from the SQA course Support Notes for National 5
Chemistry:
Task 2
Assessment Standards 2.2 and 2.3 can be achieved using one or two pieces of evidence
covering work done on different occasions.
Assessors should record evidence of achievement of Outcomes and Assessment Standards.
The table shown is one way of recording the evidence. This table is not mandatory.
This candidate has passed both Assessment Standards 2.2 and 2.3
Isotopes
An isotope is an atom with the same number of protons and electrons, but a differing number of
neutrons. Isotopes are all variants of a particular chemical element.
The nuclide notation of an isotope tells you the atomic and the mass number of that particular
isotope. The atomic number is the same as the number of electrons and the number of protons.
In an atom, each proton and neutron has a mass off 1amu (atomic mass unit), however the
relative atomic mass of an electron is almost 0amu. This means that the mass number of an
atom is the number of protons plus the number of neutrons.
Americium 241 was discovered in 1944 and is used in a common household object. Americium
(Am) is a substance made by scientists and has an atomic number 95. The nuclide notation for
americium is:
241
Am
95
The isotope americium 241 is used in some domestic smoke detectors. It has a half life of 432
years which means it will take 432 years for half of the substances to decay. It can be used in
smoke detectors because it emits and alpha particle which doesn’t penetrate very far stopping in
a few centimetres of air. As the half life is 432 years this isotope will last for a long time and will
not need to be replaced.
241
Am
95
237
Np +
93
4
He
2
The alpha particles are constantly released and knock electrons off the atoms in air. This makes
these atoms into ions which are attracted to the negatively charged plate and the electrons are
attracted to the positively charged plate generating a small current. When smoke enters the
chamber the smoke particles attach to the ions and reduce the current flowing. This drop in
current triggers the alarm. These are very sensitive detectors.
The amount of Americium 241 used in smoke detectors is very small and the alpha particles will
not escape from the chamber. This means they are safe for household use. This isotope has had
a very positive effect on society as these smoke detectors are cheap, easy to install and have
saved many people’s lives from fire. However as these smoke detectors contain a radioactive
source they must be disposed of correctly.
Assessment Standard
2.2 Describe an
application
2.3
Describe a
chemistry issue in
terms of the effect
on the environment/
society
Evidence Required
The application is linked to a
key area of the course
Evidence Produced
Nuclear chemistry/ isotopes
Application stated
Smoke detectors
Appropriate chemistry
knowledge is used to describe
the application
Description of how a smoke
detector works is given.
The chemistry issue is linked
to a key area of the course
Nuclear chemistry/ isotopes
A relevant issue is stated
Alpha particle, disposal
Appropriate chemistry
knowledge is used to describe
its effect
Nuclear equation given , alpha
radiation, small amount used,
correct disposal