Download I. Ch. 21.1 Nuclear Radiation

Unit 21 Guided Notes: Nuclear Chemistry
I.
Ch. 21.1 Nuclear Radiation
A.
Changes in Matter
1.
Matter can undergo three types of changes.
a)
Physical Change – change in __________________________ but not identity.
b)
Chemical Change – production of ___________ _______________________ with different properties –
same elements just rearranged – usually involves valence electrons.
c)
Nuclear Change – forms different ____________________ from what you started with.
(1)
B.
C.
Nuclear changes involve changes in the nucleus of an atom.
Radioactivity – spontaneous emission of __________ or ________________________ from certain elements (like uranium).
1.
also known as radioactive decay
2.
rays and particles emitted from a radioactive source are called nuclear _____________________.
Radioactivity is an example of a nuclear reaction.
1.
Purpose of radioactive decay is for an _______________________ _____________________to become stable.
2.
Nuclear reactions begin with unstable isotopes known as radioisotopes.
3.
Atoms become stable when changes occur in the ______________________.
4.
These changes are always accompanied by the emission of large amounts of energy.
5.
Unlike chemical reactions, nuclear reactions are not affected by changes in temperature, pressure, or the presence
of catalysts.
6.
Nuclear reactions of given radioisotope cannot be slowed down, sped up, or stopped.
7.
Radioactive decay is a ________________________ process.
8.
If the product of a nuclear reaction is unstable, it will decay __________________.
9.
The process continues until unstable isotopes of one element are changed, or transformed, into stable isotopes of a
different element.
10.
These stable isotopes are not radioactive.
11.
Nuclear _____________________ is emitted during radioactive decay.
12.
There are three main types of nuclear radiation: ______________ radiation, ___________ radiation, and
__________________radiation.
D.
Types of Radiation
1.
Alpha Radiation
a)
An alpha particle (α) is two protons and two neutrons bound together and is emitted from the nucleus
during some kinds of radioactive decay (also referred to a as a helium nucleus).
b)
Alpha particles have a ________________ charge
c)
In nuclear equations, an alpha particle is written as:
(1)
Example:
(2)
When an atom loses an alpha particle, the atomic number of the product is lowered by two and
the mass number decreases by four.
d)
In balanced nuclear equations, the sum of the _________ numbers on the right must equal the sum on
the left.
e)
This is also true for the _______________ numbers.
f)
Alpha particles are the least penetrating type of radiation.
(1)
2.
Sheet of paper or the surface of your skin can stop them.
Beta Radiation
a)
A beta particle (β) is an electron emitted from the nucleus during some kinds of radioactive decay.
b)
A beta particle is formed when a neutron breaks apart into a proton and an electron.
c)
The proton remains in the nucleus while the _________________ is ejected.
d)
The -1 refers to the charge of the electron and the 0 refers to the mass (essentially zero).
(1)
Example:
(2)
When an atom loses a beta particle, the atomic number of the product is increased by one;
however, the mass number remains the same.
e)
Since a beta particle has less charge and much less mass than an alpha particle, beta particles are
__________ _________________________ than alpha particles.
(1)
3.
Beta particles can pass through paper but are stopped by aluminum foil or thin pieces of wood.
Gamma Radiation
a)
Gamma rays () are high-energy waves emitted from a nucleus as it decays.
b)
Gamma rays have no mass and no electrical charge. Therefore, gamma radiation does not alter the
atomic number or mass number of an atom.
c)
Nuclei often emit gamma rays along with ______________ or _____________ particles.
d)
Gamma rays are the _____________ penetrating type of nuclear radiation.
(1)
Easily pass through paper, wood, and human body (extremely dangerous).
(2)
They can be stopped, although not completely, by several meters of concrete or several
centimeters of lead.
E.
Nuclear Equations Sample problems
1.
Radium-226 is a radioactive isotope that decays by releasing an alpha particle. Write a nuclear equation for the
radioactive decay of radium-226.
2.
Potassium-40 decays by releasing a beta particle. Write a nuclear equation that represents the radioactive decay of
potassium-40.
F.
II.
Reflection
Ch. 21.2 Nuclear Stability and Half-Life
A.
B.
More than 1500 different isotopes are known. Of those, only _____________ are stable and do not decay over time.
1.
One factor that affects the stability of nucleus is the ratio of neutrons to protons.
2.
Too many or too few neutrons relative to the number of protons makes the nucleus unstable.
3.
A neutron vs proton plot of stable nuclei form a pattern called the band of stability.
Band of Stability
1.
For elements with atomic numbers 20 or less, this ratio is about 1:1. Above atomic number 20, stable nuclei have
____________ neutrons than protons.
2.
The band of stability can be explained by the relationship between the nuclear force and the electrostatic forces
between protons.
a)
As the number of protons in a nucleus increases, the _____________________ electrostatic force
between protons increases faster than the nuclear force.
b)
More neutrons are required to increase the nuclear force and stabilize the nucleus.
c)
Beyond the atomic number 83, bismuth, the repulsive force of the protons is so great that ________
stable isotopes exist.
C.
Half-Life
1.
Every radioisotope has a characteristic rate of decay, which is measured by its half-life.
2.
Half-life is the time required for one-half of the nuclei in a radioisotope sample to decay.
3.
During each half-life, half of the remaining radioactive atoms decay into atoms of a ___________
__________________.
4.
Each radioactive nuclide has its own half-life. Half-lives can be a short as a fraction of a second or as long as billions
of years.
a)
5.
lives.
One isotope that has a long half-life is uranium-238.
(1)
4.5 billion years
(2)
Decays through a complex series of unstable isotopes to the stable isotope of lead-206.
The following equation can be used to calculate how much of an isotope will remain after a given number of half-
(1)
A = Ao x (1/2)n
(a)
A stands for the amount remaining, Ao for the initial amount, and n for the number of
half-lives.
D.
Half-Life Sample Problem
1.
E.
III.
Phosphorus-32 has a half-life of 14.3 days.
a)
How long is four half-lives?
b)
lives?
If you started with 24.0 g of phosphorus-32, how many grams of the isotope remain at the end four half-
Reflection
Ch. 21.3 Fission and Fusion
A.
Nuclear Fission
1.
What happens in a nuclear chain reaction?
a)
When the nuclei of certain isotopes are bombarded with neutrons, they undergo _________________,
the splitting of a nucleus into smaller fragments.
b)
In a chain reaction, some of the neutrons produced react with other fissionable atoms, producing more
neutrons which react with still more fissionable atoms.
2.
Nuclear fission can release enormous amounts of ____________________.
a)
The fission of 1 kg of uranium-235 yields an amount of energy equal to that produced when 20,000 tons
of dynamite explode.
b)
Nuclear reactors used _________________________ fission to produce useful energy.
c)
Reaction takes place within uranium-235 or plutonium-239 fuel rods.
d)
Much of the energy produced is in the form of heat.
e)
A fluid, usually liquid sodium or water, removes heat from the core (coolant).
f)
The heated fluid is used to change water into ___________________, which drives a turbine that
generates electricity.
g)
B.
Nuclear Reactors
1.
The control of fission in a nuclear reactor involves two steps, neutron moderation and neutron absorption.
a)
Neutron Moderation is a process that ____________ ________________ neutrons so the reactor fuel
(uranium-235 or plutonium-239) captures them to continue the chain reaction (water or graphite serves as
moderators).
2.
Neutron Absorption is a process that decreases the number of slow-moving neutrons. Control rods, made of a
material such as cadmium, are used to absorb neutrons.
C.
Nuclear Waste
1.
Fuel rods from nuclear power plants are one major source of nuclear waste.
a)
Why are spent fuel rods from a nuclear reaction stored in water?
(1)
Water cools the spent rods, and also acts as a radiation shield to ________________ the
radiation levels.
D.
Nuclear Fusion
1.
How do fission reactions and fusion reactions differ?
a)
Fusion occurs when nuclei combine to produce a nucleus of greater mass. In solar fusion, hydrogen nuclei
(protons) fuse to make helium nuclei and two positrons.
2.
Fusion reactions, in which small nuclei combine, release ______________ ______________ _________________
than fission reactions, in which large nuclei split.
3.
The use of controlled fusion as an energy source on Earth is appealing.
a)
The potential fuels are inexpensive and readily available.
b)
Reaction of hydrogen-2 nucleus and hydrogen-3 combine to form a helium nucleus.
c)
The problems with fusion lie in achieving the high temperatures necessary to start the reaction and in
containing the reaction once it has started.
E.
Reflection