Title: Nuclear Chemistry
1Nuclear Chemistry
- DHS Chemistry
- Chapters 4 and 25
2Little House on the Prarie
3Review Structure of an Atom
4Structure of an Atom
- An atom consists of three types of subatomic
particles, protons, neutrons, and electrons.
5Structure of an Atom
- Protons and neutrons are located in the nucleus
- Electrons are in a cloud surrounding the nucleus.
- The number of protons is equal to the atomic
number.
6Structure of an Atom
- If the atom is neutral, the number of electrons
is equal to the number of protons. - The mass number is equal to number of protons
number of neutrons.
7Structure of an Atom
- Elements with the same number of protons, but
have different numbers of neutrons is called an
isotope.
8Structure of an Atom
Protons Neutrons Electrons
Symbol P no e-
Charge 0 -
Location Nucleus Nucleus Electron cloud
Relative mass 1 amu 1 amu negligible
9Whats a chemical reaction?
10Chemical Reactions
11Why Call it Nuclear Chemistry?
See unitedstreaming.com
12Chemical VS. Nuclear
- Nuclear reactions are caused from unstable nuclei
becoming stable through radioactive decay. - Releasing particles and high-energy waves
- Alters the number of nuclear particles (neutrons
and protons). - Nuclear reactions are very different from
chemical reactions.
13Chemical Changes
- 1. Occur when bonds are broken and formed.
- 2. Atoms remain unchanged, though they may be
rearranged. - 3. Involve only valence electrons.
- 4. Associated with small energy changes.
- 5. Reaction rate is influenced by temperature,
pressure, concentration, and catalyst.
14Nuclear Changes
- 1. Occur when nuclei emit particles and/or rays.
- 2. Atoms are often converted into atoms of
another element. Thus their identity changes. - 3. May involve protons, neutrons, and electrons.
- 4. Associated with large energy changes.
- 5. Reaction rate is not normally affected by
temperature, pressure, or catalysts.
15What is an isotope?
16Isotope Examples
Mass Numbers
Atomic protons
Lithium - 6
Lithium - 7
17Isotopes
- Isotopes are atoms of the same element that vary
in their number of neutrons, thus they have
different mass numbers. - The convention for writing isotope names is first
the element name dash and then the mass number.
18For example Carbon-14, carbon-12 carbon-13
- How many protons and neutrons does each of the
isotopes of carbon have? - Carbon 14 8 neutrons, 6 protons
- Carbon 12 6 neutrons, 6 protons
- Carbon 13 7 neutrons, 6 protons
Mass Number (protons neutrons)
19More on Isotopes
- When an isotope is unstable it is called a
radioisotope. - To gain a more stable configuration, the nuclei
emit radiation. - The resulting stable atom is called the daughter
product. - This is called radioactive decay.
20Strong Nuclear Force
- The dense nucleus has two different kinds of
nuclear particles (protons neutrons) closed
packed together. - The protons are positively charged nucleons.
- The neutrons are neutral nucleons.
- All of the protons in the nucleus repel each
other and cause an electrostatic force that
pushes the nucleus apart.
21- However, there is a force holding the nucleus
together. - The strong nuclear force is a force that acts
only on subatomic particles that are extremely
close together. - If the strong nuclear force overcomes the
electrostatic force, the nucleus stays together.
22Neutron to Proton Ratio
- The strong nuclear force is not always strong
enough to overcome the electrostatic force. When
this happens the nucleus breaks apart. The
stability of the nucleus can be determined by the
ratio of neutrons to protons.(n/p)
23Neutron to Proton Ratio
- Elements with low atomic numbers are most stable
when the neutron to proton ratio is 11. - As the atomic number increases, more and more
neutrons are needed to overcome the electrostatic
force. - Thus, the stable ratio of neutron to proton
increases as the atomic number increases. - 1.51 is the largest ratio for a stable nucleus.
24Example Determine the neutron to proton ratio
for Lead-206. Is it stable?
- Lead 206
- 82 protons
- 124 neutrons (206 82)
- 124 1.51 ? stable
- 82 1 ratio
25Nuclear StabilityNeutron Protons
- Stable if
- Smaller than Fe 1
- 1
- Between Fe Pb
- 1-1.5
- 1
- Bigger than Pb
- 1.5
- 1
26Extra Practice
- Calculate the neutron to proton ratio, and
determine if the isotope is stable. - 1.
- 2. U- 293
22 ? 11
stable
20192 ? 2.181
unstable
27The Band of Stability
- The graph on the right plots the neutrons versus
protons. The band created is called the band of
stability. Anything that falls outside of that
band is radioactive. - All elements with an atomic number greater than
83 are radioactive.
28III. Radioactivity
29Radioactive Substances
- Bananas
- Atomic fire ball candies
- Colored gemstones (blue topaz)
- Fiesta Ware
- Table ware that contained unsafe amounts of
radioactive Uranium - Uranium for color glaze. Up to 14 can be Uranium
30Geiger Counter
31Types of Radiation
32The experiment
33Types of Decay
- Nuclear reactions change an atom of one element
to an atom of another element. This process is
called transmutation. In a nuclear reaction
there are three common types of radiation that
are emitted alpha, beta, and gamma. The first
two are involved in transmutation, changing the
identity of the atom.
34 Properties of Alpha, Beta, and Gamma Radiation Properties of Alpha, Beta, and Gamma Radiation Properties of Alpha, Beta, and Gamma Radiation Properties of Alpha, Beta, and Gamma Radiation
Property Alpha(a) Beta (ß) Gamma (?)
Composition Alpha particles Beta particles High-energy electromagnetic radiation
Description of Radiation Helium Nuclei Electrons Photons
Charge 2 1- 0
Relative Mass heaviest lightest 0
Relative Penetrating Power Blocked by paper Blocked by metal foil Not completely blocked by lead or concrete
35- Emit means to give off or release
36Alpha Particles
- Alpha particles contain the same composition as a
helium nucleus. Out of all of the radiation
particles, alpha particles move the slowest and
are the least penetrating. As a result of alpha
decay, the mass number decreases by 4 and the
atomic number decreases by 2.
or
37Alpha decay
38Beta Particles
- Beta particles are similar to an electron except
they come from the unstable nucleus of the atom.
Beta particles are formed and ejected when a
neutron decays to a proton and an electron. The
proton stays in the nucleus and the electron is
the beta particle. Beta emission is a constant
flow of quick moving electrons that can be
stopped by a metal foil. As a result of beta
decay the atomic number increases by one. The
mass number does not change.
39(No Transcript)
40Gamma Rays
- Gamma rays are short wavelengths (photons) that
move the quickest of all the types of decay, and
the most harmful! They are very high-energy
electromagnetic radiation. These rays often are
released at the same time as an alpha or beta
particle. The ray is the energy lost in the
reaction. Gamma emission does not affect the
atomic number or the mass number of the isotope.
41Gamma Rays
- Are very dangerous!!
- (write that down)
42C. Gamma ( ) Emission
- usually occurs along with other forms of
radiation. - Gamma particle is emitted
- No change in mass number
- No change in atomic number
43(No Transcript)
44Practice Problems
1. Why is radiation given off? 2. What is the
most penetrating particle? 3. What is a main
difference between a nuclear reaction and a
chemical reaction? 4. Is Carbon-14 radioactive?
Why or Why not?
45III. Balancing Nuclear Reactions
46Balancing Nuclear Reactions
- In nuclear reaction equations we account for all
of the changes in the mass number and atomic mass
that occur through the decay of the nucleus. - To verify this, we include the mass number and
atomic mass of every particle or atom involved in
the reaction.
47Solving Problems
- When solving/balancing a nuclear reaction,
- Look to find the difference of the mass numbers
and atomic numbers between the reactants and the
products. - This will indicate the particle that was released
or the atom that was formed. - Make sure you have the same total mass number and
atomic number on both sides of the equation.
48Nuclear Equations
49Nuclear Reactions
50Ex 1 Write a balanced equation for the alpha
decay of polonium-210
51Ex 2 Write a balanced equation for the beta
decay of carbon-14
52Practice
- Fill in the blank with the proper radiation
particle or isotope - 1)
- 2)
- 3)
- 4)
53Examples
- Ex 1. Write an equation for the alpha decay of
Protactinium-231 - Ex. 2
54III. Radioactive Decay Rates
55Radioactive Decay Rates
- A. Half-Lives
- We measure radioactive decay in terms of half-
lives. - A half life is the time it takes for half of a
radioactive sample to decay.
56Candy Bar Bandits
- There is a candy bar left in the teachers
lounge. Every 5 minutes a teacher walks in, looks
at the candy bar, breaks the candy bar in half
and eats it. If the candy bar originally had a
mass of 20 grams, how much is left after 4
teachers have a taste?
57Keeping Track
A T
0 1 2 3 4 5 6 7 8 20g 10g 5g 2.5g 1.25g 0 5 min 10 min 15 min 20 min
58Candy Bar
59Keeping Track
A T
0 1 2 3 4 5 6 7 8 20g 10g 5g 2.5g 1.25g 0 5 min 10 min 15 min 20 min
60Example
- The half life of Carbon-14 is approximately 5730
years. If you had 12g of Carbon-14 today, in
5730 years you would only have 6g. The missing
6g decayed and turned into Nitrogen 14. And, in
another 5730 years you will have 3g of Carbon-14
left and then in 5730 more years you would only
have 1.5g of Carbon-14 left. Every 5730 years
your sample is cut in half.
61Practice
- What is the half-life of the sample in the graph?
11 billion years
62Half-Lives
of HLs Remaining mass
1 Original Mass x (1/2) Org. Mass x (.5)1 0.5
2 Original Mass x (1/2) x (1/2) Org. Mass x (.5)2 0.25
3 Original Mass x (1/2) x (1/2) x (1/2) Org. Mass x (.5)3 0.125
4 Original Mass x (1/2) x (1/2) x (1/2) x (1/2) Org. Mass x (.5)4 0.0625
5 Original Mass x (1/2) x (1/2) x (1/2) x (1/2) x (1/2) Org. Mass x (.5)5 0.03125
6 Original Mass x (1/2) x (1/2) x (1/2) (1/2) x (1/2) x (1/2) Org. Mass x (.5)6 0.015626
Ratio of remaining mass to original mass
Remaining mass
63In the box
- Amount Remaining
- initial amount (1/2)HL
- initial amount (0.5HL)
- HL of half lives
Total Time Passed of Half Lives Time of one
HL
64Ex. 1 If gallium-68 has a half-life of 68.3
minutes, how much of a 10.0 mg sample is left
after 342 minutes?
HL A T
0 1 2 3 4 5 6 10mg 5mg 2.5mg 1.25mg .625mg 0.3125 0 68.3 136.6 204.9 273.2 341.5
0.3125 mg
65Ex. 1 If gallium-68 has a half-life of 68.3
minutes, how much of a 10.0 mg sample is left
after 342 minutes?
Amount Remaining (Initial amount) (0.5) n n
of half lives that have passed 342 total
minutes / 68.3 minutes half lives
Ans 0.3125 mg
66More Examples
- Ex. 2 If the passing of 116 years leaves 25.00
mg of an original 400 mg sample of Strontium-90,
what is the half life of Strontium-90?
HL A T
0 1 2 3 4 5 6 7 8 400 200 100 50 25mg 0 116y
116/4 29 years
67Dont get it? Here it is in words.
- If you are trying to solve for the amount of
element left, divide the time passed from the
half life and that will give you the amount of
half lives your sample has had. You can then
divide your original mass of sample by 2 as many
times as you have half lives. - If you are trying to solve for the half life of
your sample, take the remaining mass and count
how many times you have to multiple it by 2 to
get your original mass. That will tell you how
many half lives have elapsed. Take that number
and divide it by the total time that has elapsed
to get the length of just one half life.
68More on Half-lives
- Because the half-life is constant, radioisotopes
can be used to date objects. - Radiochemical dating is the process of
determining the age of an object based on the
amount of a particular radioisotope is
remaining in the object.
69Practice
- Iron-59 is used in medicine to diagnose blood
circulation disorders. The half-life of iron-59
is 44.5 days. How much of a 2000 mg sample will
remain after 133.5 days?
HL A T
0 1 2 3 4 5 6 7 8 2000 1000 500 250 0 44.5 89 133.5
250 mg of the sample
70Practice
- After 2 years, 1.99 g of a radioisotope remains
from the sample that had an original mass of 2.00
g. What is the half-life of this isotope?
200 years
71More Practice
- Solving Half-Life Problems
- Strontiums half life of the radioisotope
strontium-90 is 29 years. If you had 10.0g of
strontium-90 today, how much would you have left
after 87 years? 1.25g - If you start off with 64 grams of some substance,
how much will you have after 3 half lives? 8g - Iodine-131 has a half life of 8 days. What
fraction of the original sample would remain at
the end of 32 days? 1/16
721) Strontiums half life of the radioisotope
strontium-90 is 29 years. If you had 10.0g of
strontium-90 today, how much would you have left
after 87 years?
- Sr-90 half-life 29 years
- How many half-lives is 87 years?
- 87years 29 years 3 half-lives
- 1
half-life - How much is left after 3 half-lives?
- 10.0g ? 5.0g ? 2.5g ? 1.25g
- start after 1 half-life
after 2 half-lives after 3 half-lives
731) Strontiums half life of the radioisotope
strontium-90 is 29 years. If you had 10.0g of
strontium-90 today, how much would you have left
after 87 years?
HL A T
0 1 2 3 4 5 6 0 29 58 87
same problem, different approach
10g 5g 2.5g 1.25g
742) If you start off with 64 grams of some
substance, how much will you have after 3 half
lives?
HL A T
0 1 2 3 4 5 6 64g 32g 16g 8g
753) Iodine-131 has a half life of 8 days. What
fraction of the original sample would remain at
the end of 32 days?
HL A T
0 1 2 3 4 5 6 1/1 1/2 1/4 1/8 1/16 0 8 16 24 32
76B. Carbon Dating
77Carbon Dating
- Carbon dating is a specific type of radiochemical
dating - All living organisms have the same ratio of
carbon-14, carbon-13, and carbon-12 as the in
atmosphere. - However, once an organism dies and there is no
new carbon intake, the unstable carbon-14 starts
to break down.
78More on Carbon dating
- Scientists calculate the ratio of carbon-12 and
carbon-13 to carbon-14 in dead organisms. - Then they compare the ratio to the atmospheres
ratio and determine how many half-lives have
passed. - With that information they can calculate how long
the organism has been dead.
79IV. Nuclear Energy
80A. Fission
81Fission
- Fission means to break apart. Nuclear fission
occurs when a nucleus splits apart into different
fragments. - This generally occurs with atoms that have a mass
number heavier than 60. - The nuclei do not always split the same way.
Scientists have found 200 different products from
the fission reaction of Uranium-235.
82More on Fission
- Another important factor of fission reactions is
that they cause a chain of reactions. - The products of the initial reaction can collide
with other molecules and cause a new fission
reaction to occur. - This domino affect could go on for a long time.
This is how an atomic bomb works.
83Fission Reaction
84Nuclear Power
- Nuclear power plants harness the energy released
in fission reactions and turn it into
electricity. - One of the main issues the power plant has to
deal with is keeping the chain reactions going,
but not letting them speed out of control. To
this date there have been two large nuclear
accidents.
85Nuclear Power
- Nuclear power plants have to be very precise in
their regulations of the reactions. Some of the
products of the fission reaction are extremely
radioactive. - To ensure safety of all living things, the waste
must be properly stored. - It can take up to twenty half-lives for such
radioactivity to reach levels safe enough for
exposure. - For some waste products this can be thousands of
years.
86Fusion
87Fusion
- Fusion means to come together.
- Nuclear fusion is the combining of atomic nuclei.
- In fusion reactions, scientists bring together
nuclei of atoms that have mass numbers less than
60.
88Fusion
- This kind of a reaction also releases large
amounts of energy. - It useful to know, that the sun is powered by
fusion reactions.