8. Read the following paragraphs to help you answer the
questionsin Step 9.
lsotope
Syrnbols
Reactions
thatresultin changed
nucleiare
called
nuclear
reactions.
These
reactions
aredifferent
fromchemical
reactions
because
theyproduce
new
elements,
which
werenotpartofthe
reactants.
Bothreactant
andoroduct
elements
innuclear
reactions
come
in
versions.
These
versions
arecalled
massnumberrefers
element
isotopes.
t o s u m opf+ * n \ 3 7 . n
symbol
for
lsotopes
areversions
ofelements
chlorine
. _ift,,,
withexactly
thesamenumber
ofprotons,
atomic
number
buta different
number
of neutrons
inthe
refersto numberof
properties
nucleus.
Thechemical
of
p* ande-in a
isotopes
arethesame.
Why?Remember neutralatom
thatchemical
reactions
involve
electrons.
Thenumber
ofelectrons
equals
the
protons
number
of
fora neutral
atom.
Thenumber
ofprotons
does
notdiffer
fromoneisotoDe
toanother.
Sothe
number
ofelectrons
remains
thesame
foralloftheatomically
neutral
isotopes,
andthechemical
interactions
donot
:,. Figure5.7Ghlorine-37;
theelement
symbol
tor
change.
is Cl.Thesuperscript
Ghloline
37represents
theatomic
Butisotooes
differ
inmass.
Toshow
mass,
orthesumof protons
andneutrons.
The
thedifferences
inmass,
chemists
use
represents
theatomicnumber,
orthenumber
of protons
symbols.
Figure
5.7shows
anexample. (andelectrons)
ina neutral
atom.
l'--'
9. Look at the atomic mass reported for chlorine in figure 5.4
help you answer Steps 9a-<. Notice that many elements rn
periodic table exist in severalisotopic forms. For example,
there are 2 primary isotopesof chlorine.
a. 'Why are there numbersto the right of the decimalpoinr
most atomicmasses
on the neriodictable?
220 | Unitl Moter
h Morvelous
b. Doesthe 2nd isotopeof chlorine havemore or fewer neutrons in its nucleusthan chlorine-37?How do you know?
lumber 37 refers to the massnumber.
c. Supposeyou had 10 g of the ionic solid sodium chloride.
'Would
there be more atoms of chlorine-3Sor chlorine-37in
this crystal?Explain your reasoning,using the atomic mass
reportedon the periodic table.
To becomefamiliar with isotopesother than chlorine-35and
chlorine-37,obtain 1 Atomic Math handout per team member.
a. Completethe handout on your own. Then checkyour
answerswith team members.
If your team cannot producethe sameanswers,consultwith
your teacher.
ond(onned
your responsesin your sciencenotebook and check
Discussany lingeringconfusionwith
with classmates.
e scientistscall neutronsnuclearglue. !7hat do you think
means?
evidenceleadsyou to think that reactionsin starsare
different from reactionslike hydrogencombustion?
forcesare large enoughto push nuclei together,a fusion
ion results.Huge amountsof energyare produced,enough
power stars.What kind of reactionsresult when forcessplit
i apart?Is the energyproducedmore, less,or about the
e as in fusion reactions?Explain your reasoning.
frgure 5.5 from Step 1 to get a senseof the amount of energy involved in
nuclei together.
el
ve just learnedabout one of the most powerful reactionsin
ion. It happenswhen tremendousforcesput nuclei of
togetherto make heavier,new elements.Just imagine.
elements on the periodic table heavier than hydrogen are
stars. Even the elements found in the ingredients for the wave
with smalleratomic masses.In fact, fusion reactionsin stars
many different nuclei that there are versionsof elements,
Moruiol
oryrer5 sror
| 221
But are fusion reactionsthe only rype of nuclearreaction?-What
thtitog;l
happenswhen forcespull apart nuclei insteadof putting
placeon Earth?
lo ih.r. reactionstake placein stars?Do they take
\trfhywould Youwant to know?
as possible
To understandany rccipe,you should know as much
'Whenyou do'
about the characteristlcpropertiesof the ingredients'
ftue for wa
y"" *iff understandwhy the final product works' That's
recipe'
loyr, uttd it's true for stars.If somethinggjel wrong withthe
eachingredienthelpsyou find an answer'And finding
"tii.t*"ii"g,o pr-obl.-, helpsscientistsbecomemore successful'
answers
In Star Power,you work individually and in a team to understand
about ator
other kinds of nuclearreactions'You usewhat you know
learn about
.,r.r.ro.. to exblain thosereactions'Along the way' you
radioactive decaY.
Moteriok
none
ondProcedure
Process
and move to a section of
1.
-' Form a learning team of 3 students
dis
the room that Jlows the group to discuss quietly without
turbing other teams.
yourself
2. Readt"hrotgh eachstep in this procedureto prepare
lead a discussionin your team about 1 of 3 important types
nuclearreactions.Then come back to this step (Step2) and
accomplisheachtask.
or
a. Select1 of the 3 readings,Fusion,RadioactiveDecay'
Fission.You will becomethe team discussionleaderfor
selectedaspectof nuclearreactions'
Each team member should selecta di{ferent reading'
head'
b. Readyour selectionand completea T-tablewith the
ings "What I Understood" and "What I'm UnsureAbout'
teach it to your
You do zol have to become an expert on the material or
you do and do not u:
Instead, you will lead a discussionexpressingwhat
about the reading.
3. Record in your sciencenotebook your bestthinking on the
to
ouestionsat the end of your selectedreading' Be prepared
Jir.rrrt yout solutionswith teammates'
by a
4 . Meet with your team again and lead your discussion
plishing StePs4a-e.
u, R."d to ih" t"u- your commentsfrom the "Vhat I
Understood" column of your T-table'
222 I UnitI
lsMorvelous
Motler
figuresftom your readingasvisual aids when you explain what you
b . RepeatStep 4a with the "S7hat I'm Unsure About" column
of your T-table.
Show your sciencenotebook to teammatesand use it to
explain how you solved each problem at the end of the
reading.
d. Make correctionsand additions to your solutions as needed
basedon what you learn from teammates.
Record important information from the 2 remaining
discussions.
r on
centiofstarscanbe10milliondegrees
they
centers
Inaway,
reactions
fuelstars.
(C)lCompare
thattemperaiure
withthe
too.Thatis becausegrade
reaction
0nEarth,
18"C,
temperature
0fEarth's
surface,
average
fuels
such
as
inhvdrocarbon
gasoline
400'C.
flame,
lromstars. ora candle
coal,
and
comes
Tounderstand
howstars
create
carbonin
those
fuelsorigmuch0fthecarb0n
youmight
which
plants
fuels,
wanttoknow
0fyears based
millions
andanimals
First,remember
how
fuseto make
carbon.
nuclei
all of thatcarboncamefromfusion
t0 make
helium,
asshown
in
hydrogen
fuses
Andthe
thattookolaceevenearlier.
figure
5.8.
is
forfusionreactions
monlocation
hot
ofstars.Infact,the
bly centers
5.8 Hydrogen
r hydrogen
to make
one
s ano
am0unls
--------|
H+H+H+H
(4H)
--------)
Energy
He
Energy
@.
e- _*B +
e n e rs v
p**e-4n+energy
proThevastenergy
duced
bytheSunresults
fromtheforcerequired
to
protons
hold
together
in
thenucleus.
This
force
is
called
theslrong
nuclear
force.
lt ismuch
stronger
thantheforcebetween
electrons
and
which
iscalled
theelectrostalic
orotons.
Howdoscientists
knowthattheelectr
forceis muchweaker
thanthestrongnuclear
force?Theyknowbecause
forcesareclosely
related
to energy.
Forparticles
thesizeof ato
Remember
thatpartofthisprocess
involvesthestronger
greater
theforce,the
theenergy
2 protons
and2 electrons
forming
2 neutrons, involved.
Chemical
reactions
likecombustion
infigure
asshown
5.9.
involve
farlessenergy
thanfusionreactions
Inastar,
hydrogen
fuses
tomake
helium. Thatis because
electrostatic
forcesaremuch
Thenhelium
canfuseto make
carbon.
lnsoect
the smaller
thanstrong
nuclear
forces.
periodic
tableandfigure5,10to decide
howmany
helium
nuclei
combine
to make
onecarbon
atom.
This
fusion
reaction
alsoproduces
huge
amounts
0f energy
withtheamounts
compared
fromchemical
reactions
likecombustion.
How?
+ lots of
energy
Theenergy
results
fromanunusual
event
in
nature.
Some
tinyfraction
ofmassconverts
to
g
pound
(1
energy.
Forexample,454
!bl)of
? |ne
L'c + energy
-+
g
hydrogen
fuses
t0make
only451 ofhelium.
. Figure
There
isa lossof3 g,0rabout
5.10Production
1 percent.
That
ofcarbon.
Helium
1 percent
isresponsible
formostoftheenergy fusesto makecarbon.
Howmanyheliumnuclei
fromtheSun.
make
onecarbon
nucleus?
Figure5.9Produclion
ofa neutron.
A neutron
forms
when
anelectron
anda oroton
combine.
@
@
224| unitI Mollerk Morvelous
n is an elementessentialfor life. Frompreviouscourses,
are someof the other elementsessentialfor life?
symbolsin a reactionto showhow carbonand helium could
to make oxygen.
a reactionto showwhat element resultswhen oxygenand
rgy is an equivalent form of matter, does fusion represent a
on of the law of conservationof matter?
does the temperature in the centersof starshave to be
ely high for fusion to occur?
ioactiwe
Decay
altersa
isnottheonlywaynature
Somenucleibreakapaftontheirownin
Youalready
decay.
called
radi0active
proddecay
onetypeof radioactive
particle.
how
Remember
thealpha
. ue $iff;;93;;
--;a-1-3-----9charsesof
____L
products
wasto Rutherford's
thealphaparticle
Parent d.,,^,.,^3,o,'1Xj[""in*n"
.
theatom.
"tur"nt-"i#ui't' o:'f;
lil
wordfora heliisanother
oarticle
the
Youcanseethisbyinspecting
Arpha
decay
oruranium.
,r urd rumnucleuS
process
1.
in
figure
5.1
shown
decay
spOnian^n,,"1
_;_-,V
breaks
^,,1lif::1]
Into
apart
une.rat_ci?..r
^^_, , The
Product
erement
d,"u';;;;:;':::,1:,Ti:1"
teaoisiormeo
,,,rtrdy.a stable
isotope
of
ililerioll225
crqrers sror
numbers
compare
Notice
howthemass
Bothsidesare
andoroducts.
between
reactants
Also,
ofmass.
equal
because
ofconservation
reactant
between
noticehowcharge
compares
product.
areequal
because
Bothsides
and
the
Remember,
atomic
is
conserved.
charge
thenumber
ofprotons
and
number
shows
periodic
table.
onthe
identifies
anelement
particles.
There
areotherradioactive
decay
particle
thealpha
Twocommon
onesbesides
gamma
particle.
Figu
andthe
thebetaparticle
propefties
ofthese
a summary
of
5.12shows
products.
radioactive
decay
0lthree
lypesol decay
Figure5.12 Properties
properties.
producls.
particle
hasunique
Eachdecay
Shortrange,
stoppedby a
pieceof paper
alpha(a)
beta(B)
Electron,_9e
gamma(7)
High-energy
radiationshoder
in wavelengih
than X-rays
234=x+0
Th
------->?
90=y+(-1)
, ,z ='flea
."Hi?1i",'i"1
Youcan
ofthorium.
, Figure5.13Betadecay
predict
product
mass
element
byc0mparing
the
numbers
andcharoes.
LOngrange,
stopped by a
few centimeters
of lead
produced
Youcanpredict
thenewisotope
process.
Themass
froma radioactive
decay
isotope
mustbeequal
number
ofthereactant
ofthedecav
thesumofthemassnumbers
isotope.
Similarly,
the
cleandtheproduct
withthe
isotope
mustbalance
ofthereactant
particle
added
tothe
charge
ofthedecay
isotope.
Figure
5.13illustrates
oftheproduct
thisooint.
of
Though
thereactants
andproducts
predicted,
radioactive
reactions
canbe
decay
decav
timeatwhichan individualradioactive
All
reaction
beDredicted.
occurs
cannot
processes
Butscienti
tivedecay
arerandom.
therateof decayof a large
candetermine
ple.Forexample,
waste
oneoftheradioactive
products
powerplantis iodine-1
ofa nuclear
requires
eightdaysto decay
A 100g sample
g
Afteranother
eightdays,
50 of iodine-l31.
remain.
only25g ofiodine-131
226 | Unit|
fihtterlsMorvelous
witha shorter
isotopes
halFlile.Naturally,
youguess
howmuchiodine-131
products
produce
ata fasterrate.
decay
half-life
Yes,the
afterthenexteightdays?
property
ofanisoisa characteristic
product
Half-life
ofdecay
is 12.5g.Theeventual
years
for
varies
from4.5billion
tope.Half-life
noblegasxenon.
forsome
ofa second
to fractions
waytothinkof uranium-238
a graphic
5.14shows
suchaseinelements,
Youwill noticehowhalfof the heavier-than-uranium
of decay.
inadvanced
created
byscientists
steinium,
This
decays
eacheightdays.
amount
facilities.
research
its
iscalled
foriodine-131
oeriod
100
DecayCurvefor
Radioactivelodine-l31
ttl
-7 5
(9
a)
Eso
63s5 = 509
o
o
o
(!
c^12.5
6.25
mass= 259
mass= 12.59
mass= 6.259
mass= 3.125g
the
byone-half
decreases
of iodine-131
eightdays,theamount
ure5.14Half-lifegraph.Every
am0unI.
is radioactivedecay different from nuclearfusion?
is radioactivedecaysimilarto nuclearfusion?
e a properly balanced radioactivedecay reaction showing
Pa-234decaysto U.234.
erminethe productelementwhenTh-230decaysby alpha
to figure 5.12 for a reminderof how alpha particlesare productsassocrwith alpha emission.
cana radioactivedecayprocesscausethe atomicnumber
F is s i o n
inoneof
tendtooroceed
Fission
reactions
putting
nuclei.
together
involves
Fusion
fission
reaction,
twoways.Inanuncontrolled
Fission
is
nuclei.
taking
apart
involves
Fission
nuclei
hitunfissioned
neutrons
high-energy
as
such
nuclear
reactions
fromother
different
nuclei
are
These
split-apart
thensplitapart.
all
even
though
decay
andfusion,
radioactive
These
alongwithmoreneutrons.
Infissionreactions,produced
changing.
thenucleus
involve
causing
an
parts.
nuclei,
neutrons
hitunfissioned
equal
nuclei
splitintoapproximately
Such
reactions.
number
of
fission
plants
power
to increasing
reactions
usefission
Nuclear
increase
inthe
produce
reaction. explosive
thisnuclear
Study
energy.
iscalleda
rateof reaction
is
teaction.
lf there
chain
luauler
+
*
*
afn
energy
.l'
u
mateenough
fissionable
!frxr
?'f
the
chain
rialto sustain
that
are
simioffission
Lookforfeatures
1,000
offission
forfeatures
lartofusion.
Look
fromfusion.
thataredifferent
numbers
como
Notice
howthemass
q,
^^^
6uu
product.
parebetween
E
The
reactant
and
o
oftheproducts
numbers
sumoflhemass
numbers
of
thesumofthemass
equals
x
Y
600
is
Thesamekindofequality
thereactants.
ttl
produced
by
Theisotopes
trueforcharge.
o
o
insize
thatareclose
have
masses
fission
E' 4oo
other.
toeach
tt
reacti0ns llc
fissi0n
reactions,
Like
fusion
greater
produce
vastly
inamounts
energy
S zoo
helps
Figure
5.'15
reactions.
thanchemical
I
youunderstand
the
Notice
thisdifference.
together
forholding
requirement
energy
ionizaReactions
suchassolvation,
nuclei.
80
160
andcombustion
energy,
tion,phase
change
mass number
joules
forsimirarely
exceed
afewhundred
reactants.
of
laramounts
Joule is a standardunit of energyequival€nt to the amount of heat required to
increasethe temperatureof 1 g of water
1"C.
lsMotvelous
Moiler
nuclei
lo holdditlerent
i Figure5.15Enegyneeded
needed
to
hold
nuclear
Theamount
of energy
logether.
withotherreactions
is immense
compared
clestogether
have
studied.
takesplace.
The
, a mightyexplosion
amountof materialrequired
to proatomic
exolosion
iscalled
thecritical
Thecriticalmassoffissionable
material
atomic
bombs
isonlv45lb.
lledfissionreaction
doesnot
Engineers
controlthenumber
offiscarefully.
Nochainreaction
starts
materials
suchaswatersurround
the
material
andabsorb
manvofthe
power
plantsuse
. Nuclear
energy
fissionreactions
to produce
heatthat
boilswater,
whichturns
turbines
toproduce
electricity.
Several
oftheoroductsoffissionreactions
isotopes
areradioactive
withverylonghalflives,
These
materials
aredifficultto dispose
ofsafely.
Oneoption
includes
burying
radioactive
wastes
underground.
Yetfission
reactions
canproduce
vastamounts
ofelectricity.
Asyoumightexpect,
engaging
debate
continues
regarding
theuseof
nuclear
00wer.
is fissionlike fusion?
is fission different from fusion?
um-236is an unstableisotopeformedwhen uranium-235
is
by a neutron.Uranium.236
then undergoesfissionand can
uce a number of products.Supposeit producesstrontium.g0
3 neutrons.What is the other product?
the nuclearreactionsin starsdue to chainreactions?Explain
r reasoning.
um-234hasa half.lifeof 24 days.How manygramsof
um-234would remainfrom 100gafter 72days?Showyour
foro Stor
w you are ready.You havethe requiredknowledgeof the
ts needed to make a star. All you need is the recioe.
know how nuclear reactions make different elements and
of elements called isotopes. Elements have different chemical
ysicalproperties.Two ways you can observethesedifferences
looking for layersof gasesand looking for differencesin spectra.