Download Chapter 28 for Chem

Special Topics for SOL 2
st
1 Power Point
Nuclear Chemistry (Chap 28)
Objective A
http://pain.health-info.org/pictures/Xray%27s/Xray.head.side.jpg
 What is radioactivity?
 What is radiation?
 What is radioactive
decay?
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
http://www.liveindia.com/news/09oct08e.jpg
 These things all sound
really bad and really
dangerous.
 But they are not.
 These things are all
associated with nuclear
reactions.
Nuclear reactor in India. The last
nuclear reactor built in the US was
constructed in 1977.
Objective A
http://goatmilk.files.wordpress.com/2008/05/mushroom-cloud1.jpg
 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.
mc2.
E=
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
http://z.about.com/d/chemistry/1/0/0/R/uranium.jpg
http://www.vanderkrogt.net/elements/images/lead_dutch_boy_paperweight.jpg
  
238U
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
http://exoplanet.as.arizona.edu/~lclose/teaching/a202/radioactive-atom.gif
 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
both).
 Radiation or nuclear radioactivity
comes in 3 types: alpha, beta and
gamma.
Objective B
http://www.zamandayolculuk.com/cetinbal/AE/alpha.jpg
 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
http://www.impcas.ac.cn/usr/wjx/zhonglz/jiangzuo/prc/alpha_decay.gif
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
radiation.
Don’t worry about
the antineutrino.
We won’t worry
about that for now.
Objective B
http://www.atomicarchive.com/Physics/Images/beta.jpg
 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
DIFFERENT element
(in this case from H to
He).
Objective B
http://www.lbl.gov/abc/wallchart/chapters/03/3.html
 The third type of radiation is gamma radiation. Gamma is NOT a
particle, like alpha or beta. Gamma rays (or γ radiation) are pure energy.
It has 0 mass and the atomic number is 0 as well.
 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).
 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
http://www.sciencegeek.net/Chemistry/Unit1/300px-Alfa_beta_gamma_radiation.svg.png
 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
particles.
 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
http://www.lbl.gov/abc/Basic.html#Nuclearstructure
 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
263Sg
 259Rf + 4α
Z: 106 = 104 + 2
 Beta radiation
Mass: 14 = 14 + 0
14C
 14N + 0β
Z: 6 = 7 + (-1)
Objective C
 There are 109 elements, but over
1,500 different possible isotopes for
those elements.
 Of those, only about 264 are stable.
The rest decay, by some form
radioactive decay, to BECOME stable.
Objective C
http://www.physics.isu.edu/radinf/natural.htm
Isotope
Half Life
Information
Carbon-14
5,730 years
Used in dating of ancient artifacts
Tritium (H-3)
12.3 years
Produced from weapons testing
Iodine-131
8.04 days
Used to treat thyroid disease
Technetium-99
2.11 x 105
years
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
unstable.
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
isotopes.
 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
lead.
Objective C
http://www.jeopardy.com/multimedia_downloads.php
 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.
 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.

93Np
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.
Objective D
http://education.jlab.org/glossary/betadecay.gif
 Beta decay occurs when a neutron in the nucleus splits into a proton and an
electron. You know there are no electrons in the nucleus. Where did it came from?
How did it get there? (Z goes up by 1; mass stays the same.)
 Closely related is “positron emission,” also called Beta-plus decay. This occurs
when a proton in the nucleus splits into a neutron and a positron. A positron has
a positive charge and is about the same mass as an electron. (Z goes down by 1;
mass stays the same.)
Objective D
http://defaultprime.com/wp-content/uploads/2009/03/halflife2.jpg
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
years.
El Samplo Problemo
hey, I took French in high school
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.
 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.
Second Objective D
(yes, it should be Objective E, but it’s not, but I just want you to
know these two definitions)
http://hyperphysics.phy-astr.gsu.edu/Hbase/nucene/u235chn.html
 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
reaction.”
 Note that 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)
http://www.asi.org/adb/02/09/he3-intro.html
 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. None of that will
be on the test, but it is kind
of interesting.
The End