IGCSE Atoms and Radioactivity Notes

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Atoms and Radioactivity
Electrons, Protons and Neutrons
All atoms are made up of electrons, protons and neutrons. There is the same amount of
protons as electrons and the number of protons is what makes the atom a particular
element.
Neutron an uncharged particle inside the nucleus.
Proton a particle, roughly the same size as a neutron, in the nucleus but positive.
Electron roughly 1800 times smaller than a proton, but carrying the same amount of
charge, but negative. These circle the nucleus.
Because there is the same amount of electrons to protons, the atom has an overall charge of
zero, while the nucleus has a charge of positive.
This is because the protons and neutrons together make up the nucleus.
The relative mass of each particle is...
Electron ­ 1
Proton ­ 2000
Neutron ­ 2000
Notation, Atomic Number and Atomic Mass
12
C 6 C
Atomic mass = number of protons and neutrons.
Atomic number = number of protons only.
Remember, the atomic number can also give you the number of electrons, unless the atom
is an isotope, which means it is charged either positively or negatively. This happens when
an atom loses or gains electrons, meaning that the number of protons and electrons are
different.
Remember, you can find the number of neutrons by subtracting the atomic number from the
atomic mass.
Ionising Radiation
These are types of ionising radiation that emit from an unstable nucleus.
Alpha Particles are helium nuclei (i.e. two neutrons and two protons no electrons)
ejected from unstable nuclei. They are heavily ionising (have large damage potency)
but only have a short range of about 10cm in air and can be stopped with paper.
Beta Particles are fast moving electrons ejected from unstable nuclei. They are less
ionising, but are more penetrating as they can travel long distances in air and can be
stopped by a sheet of aluminium.
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Gamma Rays are photons of high energy electromagnetic waves. They have a low
ionising power, but are highly penetrating and can only be stopped with tens of cm of
lead.
Radiation Penetrating Power Ionising Power Stopped By...
Alpha Low High Paper
Beta Medium Medium Thin aluminium
Gamma High Low Thick lead
Nuclear Transformations
Radioactive forms of some elements (called isotopes) will decay over time randomly,
emitting radioactivity. As Gamma is rays, it has no direct effect on the radioactive atoms
configuration.…read more

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Medical Uses
Food and Drink
Buildings
Nuclear Power and Weapons.
Radioactive Decay and Halflife
Although radioactive decay is a random process, and impossible to predict, we can predict
from previous measurements the percentage of unstable atoms in a sample that will decay in
a given time.
The rate of decay is measured in Becquerel's ­ one Bq is one decay per second.
The halflife of a radioactive substance is the time taken for half the original number of
unstable nuclei to decay.…read more

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