Chapter 7 Student Guided Notes
7.1 Atomic Theory and Radioactivity
General Information
Natural background radiation exists all around us.
• This radiation consists of __________________________________________
being emitted from a variety of materials.
Radioactivity is the release of high energy particles or waves.
• Being exposed to radioactive materials can be __________________________.
o X-rays, radiation therapy and electricity generation are beneficial.
o High energy particles and waves can do damage to DNA in our cells.
• When atoms lose high energy particles and waves, ions or even new atoms can
be formed.
• ____________________________________ are called ________________
when they leave the atom
The Electromagnetic Spectrum
Invisible Rays
Radiation is _____________________, but can be difficult to detect.
• _________________________ named X-rays with an “X” 100 years ago
because they were previously unknown.
• ________________ realized uranium emitted seemingly invisible energy as well.
• ____________________ and her husband
Pierre named this energy radioactivity.
o Early discoveries of radiation relied on
photographic equipment
• Later, more sophisticated devices such as the
______________________ were developed
to more precisely measure radioactivity
Radium salts, after being placed on a photographic
plate, leave behind the dark traces of radiation.
Isotopes & Mass Numbers
______________________ are different atoms of the ____________________, with
the _________________ between the two atoms being the ____________________
in the nucleus.
• Isotopes have ________________________________________ - and therefore
the same atomic number - as each other.
• By having different numbers of neutrons, isotopes have ___________________
o Isotopes of an element have the ______________ and same __________
Mass number refers to the ___________________________ in an isotope
o Atomic mass = proportional average of the mass numbers for all isotopes
of an element.
 19.9% of boron atoms have 5 neutrons, 80.1% have 6 neutrons
 19.9% have a mass number of 10, and 80.1% have a mass number
of 11
 (.199 * 10) + (.801*11) = 10.8 = atomic mass of boron
Representing Isotopes
Isotopes are written using standard atomic notation.
• ________________________________________________________________.
Potassium has three isotopes,
Potassium is found in nature in a certain ratio of isotopes
o ________ is potassium-39, _______ is potassium-40, and _______is
o Atomic mass = (____ x 39) + (_____ x 40) + (_____ x 41) = 39.1
Radioactive Decay
Unlike all previously discovered chemical reactions, _________________________
resulted in the formation of completely ___________________.
• Radioactivity results from having an unstable nucleus.
• When these nuclei ________________________________________________.
o Radioactive decay releases energy from the nucleus as radiation.
o Radioactive atoms ______
often as different atoms.
o An element may have only
certain isotopes that are
 These are called
Radioisotope uranium-238 decays in several stages until it finally becomes lead-206
Three Types of Radiation
Rutherford identified three types of radiation using an electric field.
• Positive ___________________ were attracted to the negative plate.
• Negative ___________________were attracted to the positive plate.
• Neutral ____________________ did not move towards any plate.
Alpha Radiation
_________________________ is a ________________________________
• _______________ charged, and are the most massive of the radiation types.
• Alpha particles are essentially the same as a ____________________.
• Alpha particles are represented by the symbols .
o Because it has two protons, it has a charge of 2 .
o The release of alpha particles is called alpha decay.
• Alpha particles are ________ and ______________________________ than the
other forms of radiation. A ______________________ will stop an alpha particle
Radium-226 releases an alpha particle and becomes
Radon-222. Radon has two less protons than radium.
Beta Radiation
Beta radiation, ___________________________________ .
• Negatively charged, and the size of an electron.
• Beta particles are represented by the symbols .
o Electrons are _____________, so beta particles are assigned a
o Since there is only an electron, a beta particle has a ________________
• Beta decay occurs when a __________________________________ + an
o The proton stays in the __________________________________.
o It takes a ___________________________ foil to stop a beta particle.
Iodine-131 releases a beta particle and becomes Xenon-131. A neutron has turned into
a proton + the released electron.
Gamma radiation is a ray of __________________, short-wavelength radiation.
• Gamma radiation has _____________________________________________, .
• Gamma radiation is the highest energy form of electromagnetic radiation.
o It takes thick blocks of lead or concrete to stop gamma rays.
• Gamma decay results from energy being released from a high-energy nucleus.
• Often, other kinds of radioactive decay will also release gamma radiation.
o Uranium-238 decays into an alpha particle and also releases gamma rays.
Nuclear equations are written
but represent changes in the
nucleus of atoms.
Chemical equations
represent changes in the
position of atoms, not
changes to the atoms
1. _______________________
2. _______________________
7.2 Half-life
General Information
It can be difficult to determine the ages of objects by sight alone.
• Radioactivity provides a method to _____________________ by measuring
_________________________ of remaining radioactive material to stable
products formed.
Carbon dating measure the ratio of carbon-12 and carbon-14.
• Stable carbon-12 and radioactive carbon-14 exist naturally in a constant ratio.
o In nature, carbon-12 appears 98.9% of the time, while one carbon-14
atom appears for every 1 trillion normal atoms.
• When an organism dies, carbon-14 stops being created and slowly decays.
o Measuring the relative amounts of carbon-12 : carbon-14 is called
o Radiocarbon dating only works for organisms less than 50 000 years old
 The half-life of carbon-14 is ____________________.
Rate of Radioactive Decay
Half-life measure the rate of radioactive decay.
• ________________________ = time required for
half of the radioactive sample to decay.
• The half life for a radioactive element is a
constant rate of decay.
• Strontium-90 has a half-life of 29 years. If you
have ___________ of strontium-90 today, there
will be ___________ remaining in _____ years.
Decay curves show the rate of decay for radioactive elements.
• The curve shows the relationship between half-life and percentage of original
substance remaining.
Common Isotope Pairs
There are many radioisotopes that can be used for dating.
• ______________ = ________________________________________________.
• _______________ = _______________________________________________.
• The rate of decay
remains constant, but
some elements require
one step to decay,
while others decay over
many steps before
reaching a stable
daughter isotope.
o ____________
decays into
in one step
o Uranium-235 decays into lead-207 in fifteen steps.
o Thorium-235 decays into lead-208 in ten steps.
Potassium 40
Radioisotopes with very long half-lives can
help determine the age of very old things.
• The potassium-40/argon-40 clock has a
half-life of ________________________.
• Argon-40 produced by the decay of
potassium-40 becomes trapped in rock.
• Ratio of potassium-40 : argon-40 shows
7.3 Nuclear Reactions
General Information
Nuclear _______________ and_____________________ are processes that involve
extremely large amounts of energy.
• Fission = ____________________________________
• Fusion = __________________________
Nuclear power plants can generate large
amounts of electricity through Nuclear
• In Canada, Ontario, Quebec and New
Brunswick currently use nuclear power.
• Canadian-made nuclear reactors are
called CANDU reactors.
• CANDU reactors are considered safe and
effective, and are sold throughout the
The Bruce Nuclear Generating Station on the shores of Lake Huron, in Ontario
Nuclear Fission
Nuclear energy used to ____________________ comes from ________________.
• Nuclear fission is the______________ of one heavy nucleus into
___________________ smaller nuclei, as well as some sub-atomic particles and
• A heavy nucleus is usually unstable, due to many + protons pushing apart.
• When fission occurs:
1. ._________________________________.
2. __________________________________.
Nuclear reactions are _________________________ chemical reactions.
• In chemical reactions, mass is conserved, energy changes are relatively small.
o There are no changes to the nuclei in chemical reactions
• In nuclear reactions, ____________________________________________.
o Protons, neutrons, electrons and/or gamma rays can be lost or gained.
o _____________________ = ____________________________
Nuclear Equations
Natural radioactive decay consists of the release of alpha, beta and gamma
Scientists can also force ( = induce) nuclear reactions by smashing nuclei with
alpha, beta and gamma radiation.
The rules for writing these equations are
the same as earlier nuclear equations
______________ of the equation
Charges must equal on both sides of the
Fission of Uranium 235
It is much easier to crash neutral neutron than a positive proton into a nucleus to
release energy.
• Most nuclear fission reactors and weapons use this principle.
, crashes into an atom of _____________________ to
create unstable _________________, which then undergoes radioactive decay.
After several steps, atoms of krypton and barium are formed, along with the
release of 3 neutrons and huge quantities of energy.
The induced nuclear fission of uranium-235. This
nuclear reaction is the origin of nuclear power and
nuclear bombs.
Chain Reactions
Once the nuclear fission reaction has
started, it can keep going.
• The ____________released in
the induced reaction can then
_______________________ on
other uranium-235 atoms.
This __________________ can quickly get out of control
o Fermi realized that materials that could absorb some neutrons could help
to control the chain reaction.
Nuclear reactors have complex systems to ensure the
An uncontrolled chain reaction can result in the release of excess energy of
harmful radiation
o It is on this concept that nuclear bombs are created.
CANDU Reactions
Canada’s nuclear research into the safe use of nuclear reactions has resulted in
the creation of ______________________________.
• CANDU rectors are found in various countries around the world.
o Canada, South Korea, China, India, Argentina, Romania and Pakistan
• The reactors are known to be safe and easy to shut down in an emergency.
o _______________________________________________________
Hazardous wastes produced by nuclear reactions are problematic.
• Some waste products, like __________,
can be re-used
• Some products are very radioactive,
however, and must be stored away from
living things.
o Most of _______________________
o It takes 20 half-lives _____________
Nuclear Fusion
_____________ = _________________________
• __________________________________, two hydrogen
nuclei join under tremendous heat and pressure to form a
helium nucleus.
• When the helium atom is formed, __________________
of energy are released.
Scientists cannot yet find a safe, manageable method to
harness the energy of nuclear fusion.
• So-called “cold fusion” would occur at temperatures and
pressures that could not be controlled.