Chapter 25

Chapter 25
Nuclear Chemistry
For Advanced Chemisty, this is part of Unit 2
For Chemistry, this is part of Unit 7
FOR ALL CLASSES, you do not need to do Chapter Notes for 25!
Special Note
S We are not going to cover Section 4 in Chapter 25. although it is very
interesting and talks about beneficial used of radiation in your
everyday life (potentially).
S 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 section 3.
S Fission = 1 large nucleus splitting apart into 2 or more smaller pieces
S Fusion = 2 small nuclei joining together to form 1 larger nucleus.
S Except for fusion and fission, those sections will NOT be on my test.
Radioactive = Unstable Nucleus
S What is radioactivity?
S What is radiation?
S What is radioactive
Nuclear Reaction means reaction
that happens in the nucleus
S These things all sound
really bad and really
S But they are not.
S These things are all
associated with nuclear
They can be very destructive, but
you need a CRITICAL MASS
S Nuclear reactions are just reactions that
occur in the nucleus. Chemical
reactions occur by electrons interacting
with each other.
S Nuclear reactions can release a lot of
E = mc2.
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.
energy, as seen in the photograph.
However, to do that, you need a “critical
mass” of radioactive material. That’s
usually quite a lot. Scientists don’t ever
use that amount accidentally.
S 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.
Uranium  Lead
  
S Nuclear reactions occur for one reason and one reason only: the nucleus
is unstable.
S They become stable by giving off radiation, and ultimately by changing
into a more stable nucleus.
S When the nucleus becomes stable, the nuclear reaction is over.
3 Flavors
S Radioactive decay is the process
by which unstable nuclei (plural
of nucleus) become stable.
α = alpha
β = beta
γ = gamma
S They become stable by giving off
radiation (particles or energy or
S Radiation or nuclear radioactivity
comes in 3 types: alpha, beta and
Alpha Particles = Helium Nucleus
S 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.
S Since an α particle has 2
protons, Z = 2. Since it
also has 2 neutrons, the
mass number is 4.
Atomic # decreases by 2
Z = 95
Z = 93
S So when a nucleus loses an alpha particle (called
alpha radiation), it loses 2 protons and 2 neutrons.
S It changes into a DIFFERENT element. It’s atomic
number decreases by 2. It’s mass decreases by 4.
Beta particle = electron
(from the nucleus)
S 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.”
S 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 radiation.
Don’t worry about
the antineutrino.
We won’t worry
about that for now.
Atomic # goes up by 1
S So when a nucleus loses
a beta particle (called β
radiation), it GAINS one
proton and the mass
remains the same.
S It changes into a
(in this case from H to
Gamma = the hyper child
S The third type of radiation is gamma radiation.
Gamma is NOT a particle, like alpha or beta.
S Gamma rays (or γ radiation) is pure energy. It
has 0 mass and the atomic number is 0 as well.
Gamma Ray is a BAND?
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??
S Gamma radiation is often released along with alpha or beta radiation.
S 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).
Atomic # doesn’t change
It came up
when I
searched on
γ radiation.
I just
thought it
looked cool.
S When the nucleus releases gamma radiation, the mass doesn’t
change and the element’s identity doesn’t change either.
S Only alpha and beta radiation cause the element to turn into a
different element.
Radiation (like love) is in the air!
S We are constantly being
Radiation suit for protection;
luckily, we don’t have to wear
bombarded with alpha,
beta and gamma
S 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.
Alpha = weakest;
Gamma = strongest
S Alpha particles have the LEAST amount of
energy. Paper can stop alpha particles.
S Beta particles have more energy than alpha,
but less than gamma. Aluminum foil or a
thin piece of wood can stop beta particles.
S 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
Writing nuclear reactions is a
piece of cake!!
S You have to be able to write nuclear reactions. Luckily, they
are very easy, if you can do some simple arithmetic.
S Alpha radiation
S Beta radiation
 259Rf + 4α
 14N + 0β
Enrico Fermi, an
Italian Nobel Prize
winner, who worked on
nuclear reactors and
quantum mechanics.
S There are 109 elements, but over 1,500
different possible isotopes for those elements.
S Of those, only about 264 are stable. The rest
decay, by some form radioactive decay, to
BECOME stable. We call those radioisotopes.
S 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.)
S Other isotopes take billions of billions of years
to decay.
As I learn new things, my
lectures have to change.
S The longest known half life is for
Bismuth crystals.
Pretty cool, huh?
which has a half life of 1.9 x 10 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.)
S As a matter of209fact, I used to tell my
students that Bi was the largest isotope
(in terms of mass) which was stable, but
that was wrong.
S 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
S It got me to thinking…
S What if EVERYTHING decays? But
what if some things decay so ridiculously
slowly as to be all but impossible to
measure it.
S It’s my hypothesis. I don’t know how to
Iron pillar in India which
has withstood corrosion
for over 1,600 years.
design an experiment to prove it yet
though (but I’m pretty sure there’s a
Nobel Prize in here somewhere).
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?
Half Lives of Common Isotopes
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.
S Many other things have half lives of minutes or days or years or decades
or centuries, or even millions of years.
S How do you know IF an isotope is stable.
S Let’s talk about the Band of Stability. The stable isotopes can be
calculated using a simple formula.
The Band of Stability
#N/#P =
S Find the value of #
Neutrons / # Protons
S If that number is greater
than or equal to 1 AND
less than or equal to 1.5,
the isotope is stable.
S So, anything less than 1
is unstable. Anything
greater than 1.5 is
The Band of Stability
S 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.
S Elements with Z < 20 generally decay by β decay.
S 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 isotopes.
S Elements with a HIGH atomic number that are unstable usually have
too many neutrons.
S They decay by α decay, primarily until they reach 206Pb, which is a
stable isotope of lead.
Elements become
other elements in
something called a
transmutation rxn.
Radioactive decay is
a transmutation
S 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.
I Lost on Jeopardy, Baby!
(anyone know that song?)
S 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 Jeopardy!
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.
S 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 in the nucleus come from?
S In a reaction form, beta decay can be
expressed as
S 0n  -1β + 1p
S 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.
Positrons are the same size and
mass as beta, but they are
positively charged.
S There is also a process where a nucleus can
emit something called a “positron.”
S When this happens, the mass remains the
same but the atomic number goes down by
S 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
S In a reaction form, positron emission can
be expressed as
S 1p  +1β + 0n
S 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.
Half Life Calculations WILL be
on the SOL (guaranteed)
picture cropped
S Half life (t½) is the time required for one
half of the nuclei in a radioactive sample
to decay.
S 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
S A = A0(½)t/T
S Where A = amount at time = t.
S A0 = original amount at time = 0.
S t = elapsed time
S T = half life (same units as “t”)
S Sounds simple enough…
El Samplo Problemo
hey, I took French in high school
S 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.
S A…let’s not use the formula
S B…let’s do use the formula
S After one half life, half should have decayed.
S 0.800 g  0.400 g
El Samplo Problemo
hey, I took French in high school
S 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.
S A…let’s not use the formula
S After one half life, half should have decayed.
S 0.800 g  0.400 g
S After two half lives, we find ourselves at the
amount listed in the problem.
S 0.800 g  0.400 g (1st half life)
S 0.400 g  0.200 g (2nd half life)
S So, 10.5 years = 2 half lives.
S Therefore 5.25 years = 1 half life.
El Samplo Problemo
hey, I took French in high school
S Co-60 decreases from 0.800 g to
Easy, too!
0.200 g in a period of 10.5 years.
From this information, what is the
half life.
S B…let’s do use the formula
S A = A0(½)t/T
S A = 0.200 g; A0 = 0.800 g;
S 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!
S 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.
S B…let’s do use the formula
S 0.200g = 0.800g x (½)10.5 years/T
S 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!
S 0.25 = (½)10.5 years/T
Use the log rule here
10.5 years/T]
times log(a)
So from
where we
left off, take
the log of
both sides.
S -0.602 = 10.5years/T x log(½)
S -0.602 = 10.5years/T x (-0.301)
S 2 = 10.5years/T
S 2 x T = 10.5 years or T = 5.25 years
The End
See you in Unit 3 for Advanced.
For Chemistry, we are finally DONE with new material, so let’s gets started
reviewing EVERYTHING ELSE we learned for the SOL, which is coming up

similar documents