1. 7.1 Atomic Theory and Radioactive Decay
Natural _________________________ exists all around us.
This radiation consists of high energy particles or waves being emitted from a variety of materials.
_________________ is the release of high-energy particles or waves.
Being exposed to radioactive materials can be beneficial or harmful.
X rays, radiation therapy, and electricity generation are beneficial.
High-energy particles and waves damage ___________ in our cells.
When atoms lose high-energy particles and waves, ions or even new atoms can be formed.
High-energy waves and particles are called radiation when they leave the atom.
The electromagnetic epectrum
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2. Searching for Invisible Rays
Radiation is everywhere, but can be difficult to detect.
______________ named X rays with an “X” 100 years ago because they were _____________________________ .
_____________ realized uranium emitted seemingly invisible energy as well.
_________________ and her husband Pierre named this energy radioactivity.
Early discoveries of radiation relied on photographic equipment.
Later, more sophisticated devices such as the ______________ counter were developed to more precisely measure radioactivity.
Radium salts, after being placed on a photographic plate, leave behind the dark traces of radiation.
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3. Isotopes and Mass Number
________ are different atoms of the same element, with the difference between the two atoms being the number of _________in the nucleus.
Isotopes have the same number of protons and therefore the same atomic number as each other.
By having different numbers of _______________, isotopes have different mass numbers.
Isotopes of an element have the same symbol and same atomic number
Mass number refers to the protons plus neutrons in an isotope
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
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4. Representing Isotopes
Isotopes are written using standard atomic notation.
Chemical symbol + atomic number + mass number.
Potassium has three isotopes,
Potassium is found in nature in a certain ratio of isotopes.
93.2% is potassium-39, 1.0% is potassium-40, and 6.7% is potassium-41
Atomic mass = (0.932 x 39) + (0.001 x 40) + (0.067 x 41) = 39.1
See page 290
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5. Radioactive Decay
Unlike all previously discovered chemical reactions, ______________ sometimes results in the formation of completely new atoms.
Radioactivity results from having an ______________________________.
When these nuclei lose energy and break apart, decay occurs.
Radioactive decay releases energy from the nucleus as radiation.
Radioactive atoms release energy until they become stable, often as different atoms.
An element may have only
certain isotopes that are
radioactive.
These are called
____________________.
See page 293
Radioisotope uranium-238 decays in several stages until it finally becomes lead-206.
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6. Three Types of Radiation
__________ identified three types of radiation using an electric field.
Positive ___________ particles were attracted to the negative plate.
Negative __________ particles were attracted to the positive plate.
Neutral ___________ rays did not move towards any plate.
See page 294
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7. Three Types of Radiation (continued) : Alpha Radiation
Alpha radiation is a stream of alpha particles.
They are positively charged, and are the _____________ of the radiation types.
Alpha particles are essentially the same as the ______________ nucleus.
Alpha particles are represented by the symbols
Because it has two protons, it has a charge of 2+.
The release of alpha particles is called alpha decay.
Alpha particles are slow and penetrate materials much less than the other forms of radiation. A _______________________ will stop an alpha particle.
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Radium-226 releases an alpha particle and becomes
Radon-222. Radon has two less protons than radium.
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8. Three Types of Radiation (continued) : Beta Radiation
A beta particle is an electron and is negatively charged.
Beta particles are represented by the symbols
Electrons are very tiny, so beta particles are assigned a mass of 0.
Since it is only an electron, a beta particle has a charge of 1–.
Beta decay occurs when a ___________ changes into a __________ + an electron.
The proton stays in the nucleus, and the electron is released.
It takes a ____________________________________ to stop a beta particle.
Iodine-131 releases a beta particle and becomes xenon-131. A neutron has turned into a proton and the released electron.
See page 296
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9. Three Types of Radiation (continued) : Gamma Radiation
Gamma radiation is a ray of _______________, _________-wavelength radiation.
Gamma radiation has no charge and no mass, and is represented by the symbol
Gamma radiation is the highest-energy form of electromagnetic radiation.
It takes thick blocks of __________________________ 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.
Uranium-238 decays into an alpha particle and also releases gamma rays.
See page 297
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10. Radiation and Radioactive Decay Summaries, and Nuclear Equations for Radioactive Decay
Nuclear equations are written like chemical equations, but represent changes in the nucleus of atoms.
Chemical equations represent changes in the position of atoms, not changes to the atoms themselves.
The sum of the __________________ does not change.
The sum of the ____________ in the nucleus does not change.
See pages
Take the Section 7.1 Quiz
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11. It can be difficult to determine the ages of objects by sight alone.
7.2 Half-life
It can be difficult to determine the ages of objects by sight alone.
Radioactivity provides a method to __________________ by measuring relative amounts of remaining radioactive material to stable products formed.
Carbon dating measures the ratio of carbon-12 and carbon-14.
Stable carbon-12 and radioactive carbon-14 exist naturally in a constant ratio.
When an organism dies, carbon-14 stops being accumulated, and slowly decays.
Carbon dating only works for organisms
less than years old.
Using carbon dating, these cave paintings of horses,
from France, were drawn years ago.
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12. The Rate of Radioactive Decay
___________ measures the ________ of radioactive decay.
Half-life = 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 10 g of strontium-90 today, there will be 5.0 g remaining in 29 years.
Decay curves show the rate of decay for radioactive elements.
The curve shows the relationship
between half-life and __________ of
original substance remaining.
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The decay curve for strontium-90
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13. There are many radioisotopes that can be used for dating.
Common Isotope Pairs
There are many radioisotopes that can be used for dating.
_______________ isotope = the original, radioactive material
_______________ isotope = the stable product of the radioactive decay
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.
Carbon-14 decays into nitrogen-14 in one step.
Uranium-235 decays into lead-207 in 15 steps.
Thorium-235 decays into lead-208 in 10 steps.
See page 307
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14. The Potassium-40 Clock
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 __________________ years.
Argon-40 produced by the decay of
potassium-40 becomes trapped in rock.
Ratio of potassium-40 : argon-40
shows age of rock.
See pages
Take the Section 7.2 Quiz
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15. Nuclear power plants can generate large amounts of electricity.
7.3 Nuclear Reactions
Nuclear ________ and ________ are processes that involve extremely large amounts of energy.
_____________ = the splitting of nuclei
_____________ = the joining of nuclei
Nuclear power plants can generate large amounts of electricity.
Ontario, Quebec and New Brunswick currently generate nuclear power.
Canadian-made nuclear reactors are called CANDU reactors.
____________ reactors are considered safe and effective and are sold
throughout the world.
The Bruce Nuclear Generating Station on the shore of Lake Huron, in Ontario
See page 312
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16. Nuclear energy used to produce power comes from fission.
Nuclear Fission
Nuclear energy used to produce power comes from fission.
Nuclear fission is the splitting of one heavy nucleus into two or more smaller nuclei, some sub-atomic particles, and energy.
A heavy nucleus is usually ________________,
due to many positive _________ pushing apart.
When fission occurs:
Energy is produced.
Neutrons are released.
_______________ are different than chemical reactions.
In chemical reactions, mass is conserved, and energy changes are relatively small.
There are no changes to the nuclei in chemical reactions.
In nuclear reactions, the actual nucleus of atoms changes.
Protons, neutrons, electrons, and/or gamma rays can be lost or gained.
Small changes of mass = huge changes in energy
Albert Einstein’s famous equation E = mc2 illustrates the energy found in even small amounts of matter
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17. Nuclear Equations for Induced Nuclear Reactions
Natural radioactive decay consists of the release of
__________, __________ and ____________ radiation.
Scientists can also create nuclear reactions by smashing nuclei with alpha, beta and gamma radiation.
The rules for writing these equations
are the same as earlier nuclear equations
Mass numbers must equal on
both sides of the equation
Charges must equal on
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18. Nuclear Fission of Uranium-235
It is much easier to crash a ____________ than a ____________ into a nucleus to release energy.
Most nuclear fission reactors and weapons use this principle.
A neutron, , crashes into an atom of stable uranium-235 to create unstable uranium-236, which then undergoes radioactive decay.
After several steps, atoms of krypton and barium are formed, along with the release of three 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.
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19. Once the nuclear fission reaction has started, it can keep going.
Chain Reactions
Once the nuclear fission reaction has started, it can keep going.
The neutrons released in the induced reaction can then trigger more reactions on other uranium-235 atoms.
This __________________ can quickly get out of control.
___________ realized that materials that could
absorb some neutrons could help
to control the chain reaction.
Nuclear reactors have
complex systems to ensure the
______________ stays at safe levels.
An uncontrolled chain reaction can result
in a violent nuclear explosion.
Nuclear bombs are created using this concept.
Nuclear Chain Reaction.
See page 318
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20. CANDU Reactors and Hazardous Wastes
Canada’s nuclear research into the safe use of nuclear reactions has resulted in the creation of _______________ reactors.
_____________ reactors are found in various countries around the world.
Canada, South Korea, China, India, Argentina, Romania and Pakistan
The reactors are known to be safe and easy to shut down in an emergency.
Heat energy produced turns electricity-generating turbines.
_____________________ produced by nuclear reactions are problematic.
Some waste products, like fuel rods, can be re-used.
Some products are very radioactive, however,
and must be stored away from living things.
Most of this waste is buried underground
or stored in concrete.
It will take 20 half-lives (thousands of years)
before the material is safe.
Inside a CANDU reactor.
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21. The fusion of hydrogen nuclei
Nuclear Fusion
Nuclear ______ = joining of two light nuclei into one heavier nucleus.
In the core of the Sun, two hydrogen nuclei join
under tremendous heat and pressure to form a
helium nucleus.
When the helium atom is formed, huge amounts
of energy are released.
Scientists cannot yet find a safe, manageable
method to harness the energy of nuclear fusion.
So-called “__________________” would occur at
temperatures and pressures that could be
controlled.
The fusion of hydrogen nuclei
See pages
Take the Section 7.3 Quiz
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