Nuclear Chemistry 2 - radioactive decay
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Transcript Nuclear Chemistry 2 - radioactive decay
Lesson 2:
It’s Greek to Me
ChemCatalyst
Uranium-238 is used in nuclear reactors
to generate electricity. In the nuclear
reactor, uranium-238 changes to lead209.
• How can atoms of uranium-238
change into atoms of lead-209?
• The nuclear reaction is initiated by
1
colliding the uranium-238 with 0 n .
What do you think this symbol
represents?
The Big Question
• What changes in the nucleus during
radioactive decay?
• Goal - Predict the result of radioactive
decay of an atom.
Notes
• A nuclear reaction happens
when the nucleus of an atom
is unstable and
spontaneously decays
emitting particles.
• There are two types of
nuclear decay, alpha and
beta. Depending on the type
of decay either an alpha
particle or beta particle is
emitted.
• Chemists use equations like the
following one to represent nuclear
reactions.
47
Ca
20
238
U
92
g
g
+
47
Sc
21
+
234
Th
90
A more detailed map
Activity
Purpose: This activity introduces you to
two common forms of nuclear decay.
It’s Greek to me…
Parent
isotope
Particle
emitted
Daughter Change
isotope
in atomic
#
# of
protons
lost or
gained
# of
neutrons
lost or
gained
Change
in mass
number
Alpha or
beta
decay?
Making Sense
• Give a specific example of how a chemist
might make gold using alpha decay. Be
specific about which isotope of gold is
made.
• Give a specific example of how a chemist
might make gold using beta decay. Be
specific about which isotope of gold is
made.
• Would the isotopes of gold prepared by
alpha and beta decay be located in the
band of stability?
Notes
• Alpha (α) decay and beta (β)decay are two
forms of nuclear decay.
• During alpha decay, a nucleus is splitting into
two smaller elements, one of which is always a
helium atom.
• Chemists use the symbol α (Greek letter) to
represent an alpha particle.
U He Th
U Th
238
92
238
92
4
2
234
90
234
90
• During beta decay a neutron inside the
nucleus of an atom emits an electron.
–This electron is a part of nuclear decay and
therefore comes from the nucleus.
• Sometimes a neutron can be split into an
electron and a proton.
• Removal of an electron from a neutron
changes the neutron into a proton
0
1
n e p
1
0
1
1
n p
1
0
1
1
140
56
Ba
140
57
La
(cont.)
• The process of splitting a large nucleus
into smaller ones is called nuclear
fission.
• Besides alpha and beta particles,
many radioactive nuclei release energy
in the form of gamma rays ( rays).
(cont.)
(cont.)
• The release of a ray does not change
the mass number or the atomic
number
– a ray has no mass.
• radiation by itself does not change
the identity of the atom.
–But ray emission usually occurs
whenever there is alpha or beta
emission.
Nuclear fission
Sometimes you can get
an atom to split by
bombarding it with
neutrons
U n Kr
238
92
1
0
91
2
142
90
Ba 5 n
1
0
Can we use nuclear chemistry to make
gold?
• What isotope would you want to start with if you
were to make gold using alpha decay? Why?
• What isotope of gold would you make?
• Is this isotope stable?
• What element would you want to start with if you
were to make gold using beta decay? Explain
• Is this isotope stable?
• Do you think chemists use nuclear decay to
make gold? Why or why not?
Check-In
• What products do you expect if an
atom of actinium-227
–undergoes alpha decay?
– Write equation
– Is the formed atom stable?
–undergoes beta decay?
– Write equation
– Is the formed atom stable?
Wrap-Up
• When changes occur in the nucleus of
an atom it is called a _____ reaction.
• When an α particle is emitted from an
atom, the nucleus loses two _____ and
two ______. An α particle is the same
as a _____ atom.
• When a β particle is emitted from an
atom, the nucleus gains a(n) _____
and loses a(n) _____. A β particle is
the same as a(n) ______.