Chapter 28

Chapter 28
Nuclear Chemistry
Special Note
 We are not going to cover Section 4 in Chapter 28.
 We are only going to cover a bit of Section 3, really
just a definition of nuclear fusion and fission. You
can ignore the “Nuclear Waste” section of Chapter
 Those parts do make interesting reading, but they
will NOT be on my test.
Objective A
 What is radioactivity?
 What is radiation?
 What is radioactive
X-ray is a type of radiation (that’s what “ray” means).
“X” just means unknown, because when it was
discovered it was something new, and so it was called
an X-ray. The name stuck.
Objective A
 These things all sound
really bad and really
 But they are not.
 These things are all
associated with nuclear
Nuclear reactor in India. The last
nuclear reactor built in the US was
constructed in 1977.
Objective A
 Nuclear reactions are just reactions
that occur in the nucleus. Chemical
reactions occur by electrons
interacting with each other.
 Nuclear reactions can release a lot of
energy, as seen in the photograph.
However, to do that, you need a
“critical mass” of radioactive material.
That’s usually quite a lot.
c is the speed of light and c2 is a
HUGE number. So even a little
bit of mass can convert to a LOT
of energy.
 In a nuclear reaction, an element CAN
change into another kind of element.
This doesn’t violate Dalton’s theory,
because it’s not a chemical reaction.
Objective A
  
decays in a series of 14 steps to 206Pb. Lead is stable.
 Nuclear reactions occur for one reason and one reason only: the
nucleus is unstable.
 They become stable by giving off radiation, and ultimately by
changing into a more stable nucleus.
 When the nucleus becomes stable, the nuclear reaction is over.
Objective A
 Radioactive decay is the process
by which unstable nuclei (plural
of nucleus) become stable.
α = alpha
β = beta
γ = gamma
 They become stable by giving off
radiation (particles or energy or
 Radiation or nuclear radioactivity
comes in 3 types: alpha, beta and
Objective B
 Alpha particles are the
same as a helium
nucleus. It has 2 protons
and 2 neutrons. It has
no electrons, and so it
has a +2 charge.
 Since an α particle has 2
protons, Z = 2. Since it
also has 2 neutrons, the
mass number is 4.
Objective B
Z = 95
Z = 93
 So when a nucleus loses an alpha particle (called
alpha radiation), it loses 2 protons and 2 neutrons.
 It changes into a DIFFERENT element. It’s atomic
number decreases by 2. It’s mass decreases by 4.
Objective B
 Beta particles are basically just
an electron. The mass number
of a beta particle is 0. For the
atomic number, we say that it
is “-1.”
 We say it’s -1, because losing a
beta particle causes the nucleus
to GAIN a proton. We’ll see
how in a little bit.
Yes, it’s in German. Not all the best stuff is in English. Notice that an electron is
“produced” when a neutron splits into a proton and an electron. Being negative, the
electron is immediately spit out of the positive nucleus. “Strahlung” means
Don’t worry about
the antineutrino.
We won’t worry
about that for now.
Objective B
 So when a nucleus loses
a beta particle (called β
radiation), it GAINS one
proton and the mass
remains the same.
 It changes into a
(in this case from H to
Objective B
 The third type of radiation is gamma radiation.
Gamma is NOT a particle, like alpha or beta.
 Gamma rays (or γ radiation) is pure energy. It
has 0 mass and the atomic number is 0 as well.
Objective B
A German band…
In 1988 Kai Hansen left his
band Helloween since he was
tired of the bad atmosphere in
and around the band. Together
with Dirk Schlächter and Ralf
Scheepers he formed a new
band called Gamma Ray.
Who will have them on iPod by
the end of this unit??
 Gamma radiation is often released along with alpha or beta radiation.
 The nucleus loses energy (it’s this energy that can be harnessed to do
productive work…like nuclear power plants…or destructive things,
like an atomic bomb).
Objective B
It came up
when I
on γ
radiation. I
thought it
 When the nucleus releases gamma radiation, the mass doesn’t
change and the element’s identity doesn’t change either.
 Only alpha and beta radiation cause the element to turn into a
different element.
Objective B
 We are constantly being
bombarded with alpha,
beta and gamma
Radiation suit for protection;
luckily, we don’t have to
wear these!
 You don’t know it and
you can’t stop it.
Luckily, the levels are
so low naturally that it
doesn’t cause us any
kind of harm.
Objective B
 Alpha particles have the LEAST amount
of energy. Paper can stop alpha particles.
 Beta particles have more energy than
alpha, but less than gamma. Aluminum
foil or a thin piece of wood can stop beta
 Gamma particles have the most energy
by far. Several meters of concrete will
stop them as will several centimeters of
lead. They easily pass through the
human body, of course.
Objective B
 You have to be able to write nuclear reactions. Luckily,
they are very easy, if you can do some simple arithmetic.
 Alpha radiation
Mass: 263 = 259 + 4
 259Rf + 4α
Z: 106 = 104 + 2
 Beta radiation
Mass: 14 = 14 + 0
 14N + 0β
Z: 6 = 7 + (-1)
Enrico Fermi, an
Italian Nobel Prize
winner, who worked on
nuclear reactors and
quantum mechanics.
Objective C
 There are 109 elements, but over 1,500
different possible isotopes for those
 Of those, only about 264 are stable. The
rest decay, by some form radioactive
decay, to BECOME stable.
 How fast they decay is dependent on the
specific isotope. Some decay rapidly…in
seconds. Fermium-258 has a half life of
0.00038 seconds (I found this in an
Iranian chemical journal…science really
is a universal language.)
 Other isotopes take billions of billions of
years to decay.
Objective C
 The longest known half life is for 209Bi
which has a half life of 1.9 x 1019 years
or 19,000,000,000,000,000,000 years.
(That’s 426,000,000,000 times
LONGER than the “accepted” age of
the Universe.)
 As a matter of fact, I used to tell my
students that 209Bi was the largest isotope
(in terms of mass) which was stable.
Bismuth crystals.
Pretty cool, huh?
 Bismuth-209 isn’t stable at all. It just
decays so slowly that it appears to be
stable to us.
Schwartz’s Hypothesis on
Nuclear Decay
 It got me to thinking…
 What if EVERYTHING decays? But
what if some things decay sooooo
slowly as to be all but impossible to
measure it.
Iron pillar in India which
has withstood corrosion
for over 1,600 years.
 It’s my hypothesis. I don’t know how
to design an experiment to prove it yet
Fe is thought to be “the most stable” element. It is the heaviest element formed by
fusion in stars. Every element above Fe is slowly decaying until it becomes Fe?
Objective C
Half Life
5,730 years
Used in dating of ancient artifacts
Tritium (H-3)
12.3 years
Produced from weapons testing
8.04 days
Used to treat thyroid disease
2.11 x 105
Beta decay product of Mo-99. Used for medical
diagnoses. Used as a γ-free source of β particles.
 Many other things have half lives of minutes or days or years or decades
or centuries, or even millions of years.
 How do you know IF an isotope is stable.
 Let’s talk about the Band of Stability. The stable isotopes can be
calculated using a simple formula.
The Band of Stability
#N/#P = 1.5
 Find the value of #
Neutrons / # Protons
 If that number is
greater than or equal to
1 AND less than or
equal to 1.5, the
isotope is stable.
 So, anything less than
1 is unstable. Anything
greater than 1.5 is
The Band of Stability
 This formula really only works for elements with an
atomic number > 20. For example, 14C is radioactive, but the
ratio 8 N / 6 P = 1.33. Elements with Z < 20 generally decay
by β decay.
 Elements with Z > 83 are always radioactive. In other words,
for Po (Polonium, named by Marie Curie for her native
Poland) and higher there are NO naturally occurring stable
 Elements with a HIGH atomic number that are unstable
usually have too many neutrons. They decay by α decay,
primarily until they reach 206Pb, which is a stable isotope of
Elements become
other elements in
something called a
transmutation rxn.
Radioactive decay
is a transmutation
 Nuclear experiments have successfully transmuted
lead into gold, but the expense far exceeds any
gain. So modern chemistry has succeeded where
the alchemists could not. In fact, it’s far easier to
turn gold into lead.
Objective C
 Transuranium elements are the
elements that have an atomic number
greater than U.
Know why Plutonium was
abbreviated Pu and not Pl?
Basically, because top
scientists really are geeks. At
least, so said Alex Trebek on
Remember when you were a
kid, and you said “P-u.”
That’s why. It probably
made him laugh every time
he thought of it.
 All of the transuranium elements are
man-made. Most of them only exist
for a second or less and then they
decay into something else. Many of
them were made by Dr. Seaborg and
his team of researchers.
for example decays by beta
decay into 94Pu, which then decays by
α decay into 92U. Uranium then
decays in a series of 14 steps to 206Pb.
Beta Decay: where does the
electron come from?
 In a reaction form, beta decay can be
expressed as
 0n  -1β + 1p
 The neutron has a mass of 1 and an “atomic
number” of 0. When the beta particle forms it
is “spit out” of the nucleus. The proton that
was formed remains in the nucleus. Since Z
goes up by 1, it is now a new element.
Objective D
 There is also a process where a nucleus
can emit something called a “positron.”
 When this happens, the mass remains the
same but the atomic number goes down
by 1.
 A positron is similar in size to an electron,
and similar in mass, but it has a positive
charge, and an atomic number of 1.
Objective D
 In a reaction form, positron emission
can be expressed as
 1p  +1β + 0n
 Again, the positron is ejected, and the
neutron remains in the nucleus. Since
the atom lost a proton, Z goes down
by 1 and a new element is formed.
Objective D
picture cropped
 Half life (t½) is the time required for one
half of the nuclei in a radioactive sample
to decay.
 As we have seen, half lives can range
from fractions of a section to billions of
Big Hairy, Easier
than it Looks
Formula Alert
Half-Life Calculations
 A = A0(½)t/T
 Where A = amount at time = t.
 A0 = original amount at time = 0.
 t = elapsed time
 T = half life (same units as “t”)
 Sounds simple enough…
El Samplo Problemo
hey, I took French in high school
 Co-60 decreases from 0.800 g to 0.200 g in a
period of 10.5 years. From this information,
what is the half life.
 A…let’s not use the formula
 B…let’s do use the formula
 After one half life, half should have decayed.
 0.800 g  0.400 g
El Samplo Problemo
hey, I took French in high school
 Co-60 decreases from 0.800 g to 0.200 g in
a period of 10.5 years. From this
information, what is the half life.
 A…let’s not use the formula
 After one half life, half should have decayed.
 0.800 g  0.400 g
 After two half lives, we find ourselves at the
amount listed in the problem.
 0.800 g  0.400 g (1st half life)
 0.400 g  0.200 g (2nd half life)
 So, 10.5 years = 2 half lives.
 Therefore 5.25 years = 1 half life.
El Samplo Problemo
hey, I took French in high school
Easy, too!
 Co-60 decreases from 0.800 g to
0.200 g in a period of 10.5 years.
From this information, what is the
half life.
 B…let’s do use the formula
 A = A0(½)t/T
 A = 0.200 g; A0 = 0.800 g;
 T= ? and t = 10.5 years
El Samplo Problemo
hey, I took French in high school
Easy, too!
But you do
need to know
Sorry! That
Algebra 2
Ok, so I lied.
Some of you
won’t think
it’s easy!
 Co-60 decreases from 0.800 g to
0.200 g in a period of 10.5 years.
From this information, what is the
half life.
 B…let’s do use the formula
 0.200g = 0.800g x (½)10.5 years/T
 0.25 =
(½)10.5 years/T
Ok, I divided both
sides by 0.800 to
get this
El Samplo Problemo
hey, I took French in high school
Easy, too!
 0.25 = (½)10.5 years/T
Log (ax) = x
times log(a)
 log(0.25) = log[(½)10.5 years/T]
So from
where we
left off, take
the log of
both sides.
Use the log rule here
 -0.602 = 10.5years/T x log(½)
 -0.602 = 10.5years/T x (-0.301)
 2 = 10.5years/T
 2 x T = 10.5 years or T = 5.25 years
Second Objective D
(yes, it should be Objective E, but it’s not, but I just want you to
know these two definitions)
 Nuclear fission is the splitting
of a large nucleus into smaller
fragments. They break apart to
form smaller elements.
 U-235 combined with a neutron
to split into Ba-144 and Kr-89 +
3 neutrons. Those neutrons can
then react with other U-235
atoms, causing a “chain
 Note the 235 + 1 = 89 + 144 + 3
Second Objective D
(yes, it should be Objective E, but it’s not, but I just want you to
know these two definitions)
 Nuclear fusion is when
smaller nuclei combine to
produce a larger nucleus.
They “fuse” together, like if
you take 2 pieces of clay
and “mush” them together.
H-2 + He-3  p + He-4 + a
LOT of energy…
25 tons of He-3 could replace 227.3
MILLION tons of fossil fuels with no
pollution and no harmful radiation!
 There is some interesting
stuff in the study guide on
nuclear fusion and He-3 on
the moon. And for more
information, check out the
link above (the Artemis
The End
Make sure you read the entire webpage at the Chapter 28 stuff link.