Introduction to Isotopes
Nuclear Chemistry, Unit 4

Curricular Map
Nuclear
Chemistry
Introduction
to Isotopes
Nuclear
Fission
Nuclear
Fusion
Radioactive
Decay
Radioactive
Half-Lives
Daily Agenda
1. Radioactive smoke article
2. Review of subatomic particles
3. Definition of an isotope
4. Practice understanding isotopes
5. In-class work/homework
Learning Goals:
 By the end of class, you should be able to:
 Navigate your way around a new way to
represent elements, called Isotope Notation
 Take information about an isotope and
represent it in Isotope Notation, and vice
versa
Great White Sharks
 Questions to answer
 Before Reading
 1. What
audience was the article intended
for?
 After Reading
 2. What do isotopes have to do with
estimating the age of sharks?
Review : subatomic particles
So…what is an isotope?
 Isotopes – atoms of the same element with
differing numbers of neutrons
Isotope Analogy: Trucks
1st Isotope of the Ford F-150 : Regular Cab
2nd Isotope of the Ford F-150: Super Cab
3rd Isotope of the Ford F-150: Crew Cab
Isotope Analogy: Trucks
So…what is an isotope?
 Isotopes – atoms of the same element
with differing number of neutrons
Isotopes of Carbon
 Carbon-12 (6 neutrons)
 Carbon-13 (7 neutrons)
 Carbon-14 (8 Neutrons)
• This notation tells
you the element and
the mass number
• Mass number = sum
of protons and
neutrons
But how do we know exactly how many neutrons an
atom has?
Isotope Notation
A few examples of isotope notation…
= Carbon-12
= Carbon-13
= Carbon-14
A few examples of isotope notation…
= Carbon-12
= Carbon-13
= Carbon-14
What about the electrons?
 If the atomic mass is the sum of the masses of the
protons and neutrons, why don’t we count mass of
the electrons?
 The mass of an electron is about 1/2000th of a
proton
 If a proton weighs 1, an electron weighs 0.0005,
and its mass is negligible
Individual Practice
 Write the following isotopes in isotope
notation:
 Uranium-232
 Cadmium-113
Fill in the missing pieces:
Isotope
Atomic
Mass Number of Number of
Isotope Name
Notation
Number Number Protons Neutrons
147
62
Isotope
Atomic
Mass Number of Number of
Isotope Name
Notation
Number Number Protons Neutrons
?
Samarium-147
62
147
62
85
Postcard to an absent student
 On a half sheet of paper:
 Summarize two main ideas from today
 Give an example of an isotope not used in
my examples
Homework/In-class work
 Isotope Notation worksheet
Curricular Map
Nuclear
Chemistry
Introduction
to Isotopes
Nuclear
Fission
Nuclear
Fusion
Radioactive
Decay
Radioactive
Half-Lives
Daily Agenda
1. Entrance card: Isotopes
2. Warmup: Averages
4. Group work: Weighted averages
5. Closing: Postcard to an absent peer
Essential Questions
 What is a weighted average?
 Why is the mass of a single isotope of an
element different than the mass on the periodic
table?
 How can the concept of weighted averages be
applied to isotopes?
Learning Goals:
 By the end of class, you should be able to:
 Explain what a weighted average is,
compared to an unweighted average
 Calculate a weighted average
 Apply the idea of a weighted average to
isotopes
 Essential question: How can the concept
of weighted averages be applied to
isotopes?
Atomic Mass
The mass on the periodic table is a weighted
average of all of the isotopes of that element.
 Essential question: What is a weighted
average?
Investigation
 Section A of chemistry has 20 students in it, and
section B of chemistry has 30 students in it. The
average grade in section A was 80%, and the
average grade in section B was 90%. What is the:
 A.) Unweighted average of all chemistry students?
 85%
B.) Weighted average of all chemistry students?
 86%
 Formula for calculating the unweighted average:
(80 + 90)
2
= 85
 Formula for calculating the weighted average:
[(20 *80) + (30 * 90)]
50
 What’s different?
= 86
Group work: Weighted and unweighted
averages
 In groups of 2-4, work on the “Concept
Work: Weighted Averages” worksheet,
through section B
Postcard to an absent peer
 On a half-sheet of paper, describe:
 A major idea from today that you
understand well
 An idea that you want to work more
with
Notes From Exit/Entrance Cards
 No memorizing formulas!
 Differentiating weighted/unweighted averages
 Our work with weighted/unweighted
averages was mostly to highlight what a
weighted average is
 Check emails for entrance card notes
Curricular Map
Nuclear
Chemistry
Introduction
to Isotopes
Nuclear
Fission
Nuclear
Fusion
Radioactive
Decay
Radioactive
Half-Lives
Daily Agenda
Notes from entrance cards
Mini-lesson: Average atomic mass
Concept mapping
Pseudo-exit cards: Concept mapping
In-class work/homework: Average atomic mass
Essential Questions
 What does the mass on the periodic table
represent?
 How is each isotope accounted for in the average
atomic mass of an element?
 How can we connect the ideas we’ve covered so
far?
Learning Goals:
 By the end of class, you should be able to:
 Calculate the average atomic mass of an
element, given the masses of the isotopes of
that element
 Map and describe the ideas we’ve covered
so far in this unit with a 70% comfort level
Atomic Mass
The mass on the periodic table is a weighted
average of all of the isotopes of that element.
Practice: Average atomic weight
 A sample of Dubnium contains two different
isotopes. The first isotope, Dubnium-265, has
an abundance of 40%. The second isotope,
Dubnium-260, has an abundance of 60%. What
is the average atomic weight of Dubnium?
 Does is match the mass of Dubnium found on
the periodic table?
Practice: Average atomic weight
 A sample of Cerium contains two different
isotopes. The first isotope, Cerium-122, has an
abundance of 4.65%. The second isotope,
Cerium-141, has an abundance of 95.35%.
What is the average atomic weight of Cerium?
 Does it match the mass found of Cerium found
on the periodic table?
Concept Mapping
 To connect what we’ve covered in this unit so
far, describe each component of the concept
`map and how it is related to what it is
connected to.
 While you’re working, if you come upon a
component of the concept map you’re not 70%
comfortable with, write it on a half-sheet of
paper (exit card) and turn it in!
 Work in pairs, please!
In-class work/homework
 “Average Atomic Mass” worksheet
 Due Friday, January 31st at the beginning
of class
QUIZ MONDAY (OPEN
NOTES)!
General Announcements
 If you are absent, you are responsible for doing the
make-up work outside of class time. Send me an
email, and we can arrange a time to meet to go
over the missing material.
 www.mauhschemistry.wikispaces.com
Notes From the Quiz
 If I wrote “see key”, I’m not posting it to the
WikiSpace because there are still people that
haven’t taken the quiz. See me for it.
Curricular Map
Nuclear
Chemistry
Introduction
to Isotopes
Nuclear
Fission
Nuclear
Fusion
Radioactive
Decay
Radioactive
Half-Lives
Daily Agenda
Video: Bernie!
Mini-lesson: Nuclear fission and fusion
In-class work/homework
Essential Questions
 How is a nuclear reaction different than a
chemical reaction?
 What is nuclear fission? Fusion?
 How does the mass of a nucleus predict the
probability of either nuclear fission or fusion
reactions?
Learning Goals:
 By the end of class, you should be able to:
 Describe how a nuclear reaction is different
than a chemical reaction
 Differentiate nuclear fission and nuclear
fusion
 Balance a nuclear reaction and identify it as
either a fission or fusion reaction
 Predict whether an element is more likely to
undergo fission or fusion, based on its mass
Chemical Reactions
 2Fe + 3H2SO4  Fe2(SO4)3 + 3H2
 Count the atoms of each element on the
left.
 Do the same for the right.
 Do they match?
Nuclear Reactions (fission, specifically)
• Count the atoms of each element on the left (not
the middle).
• Count the atoms of each element on the right (not
the middle).
• Do they match?
One Missing Component of Fission
Reactions
 Energy!
+ Lots and
Lots of
Energy
Comparing Fission & Fusion
So…
 Energy is released by splitting very large nuclei or
by combining two small nuclei
 Iron is the “middle” atomic weight
 Atoms larger than iron are more likely to undergo
fission
 Atoms smaller than iron are more likely to undergo
fusion
Comparing Fission & Fusion
Fission or Fusion?
Daily Agenda
Warm-up: Chemistry lab write-up rubric
Example: Determining purpose using an abstract
Individual/small group work: Upacking peerreviwed literature
Essential Questions
 How is a peer-reviewed journal article
organized in terms of breadth and specificity?
 What goes into a research project?
Learning Goals
 By the end of class, you should be able to:
 Analyze a graph’s data in terms of the
variables used on the axes
 Summarize the purpose, methods, and
implications of a research paper
 Identify the methods and instrumentation
used to gain data in a study
Example: Abstract

The nuclear accident of Fukushima Dai-ichi (Japan) which
occurred after the tsunami that impacted the northeast
coasts of Japan on March 11th, 2011 led to significant
releases of radionuclides into the atmosphere and resulted in
the detection of those radionuclides at a global scale. In order
to track airborne radionuclides from the damaged reactors
and to survey their potential impact on the French territory,
the French Institute of Radiation Protection and Nuclear
Safety (Institut de Radioprotection et de Sureté Nucléaire
IRSN) set up an enhanced surveillance system to give quick
results as needed and later give quality trace level
measurements. Radionuclides usually measured at trace
levels such as 137Cs and in a very sporadic way 131I were
reported.
Curricular Map
Nuclear
Chemistry
Introduction
to Isotopes
Nuclear
Fission
Nuclear
Fusion
Radioactive
Decay
Radioactive
Half-Lives
Daily Agenda
Warmup: Chernobyl
Mini-lesson: Radioactive decay
Individual/small group work: Predicting
decay products
Homework: Balancing radioactive decay
reactions
Essential Questions
 What is spontaneous decay?
 Why does an atom spontaneously decay?
 How can we predict spontaneous decay
products?
Learning Goals:
 By the beginning of next class, you should be
able to:
 Define spontaneous decay
 Explain why spontaneous decay happens
 Analyze the “belt of stability”
 Predict decay products and balance a
nuclear reaction
Spontaneous Decay
 Definition: the process by which an unstable
atom emits particles from its nucleus with the
intent of becoming more stable
 What is this “stability” concept you speak of?
Example
 Two isotopes:
 Silicon-30
 Silicon-28
 What are their proton:neutron ratios?
 Which isotope is more stable?
 Which isotope is more likely to emit a
particle?
What particles are emitted?
Can we predict decay products?
Example
 Predict the decay products (and write the
reaction):
 Phosphorus-33
 Lawrencium-260
Upcoming Class Meetings
 Friday (2/14) – Quiz Review
 Tuesday (2/25) – Quiz
Post-Quiz Homework
 Read section C.1 , starting on page 521.
 Answer the following questions, on pages
538 and 539:
 1,2,3,4,20,21,24
Curricular Map
Nuclear
Chemistry
Introduction
to Isotopes
Nuclear
Fission
Nuclear
Fusion
Radioactive
Decay
Radioactive
Half-Lives
Daily Agenda
Pennies!
Mini-lesson: Modeling half-lives
Individual/small group work: Half-life
equations and tables
Homework: Half-lives…and more!
Essential Questions
 How can radioactive decay be modeled?
 How can we describe radioactive decay?
Learning Goals:
 By the beginning of next class, you should be able
to:
 Define half-life
 Describe the exponential decay function in
terms of half-lives and amount of starting
material
 Determine half-life for an element, given a rate
of decay (or vice versa)
 Use an equation to determine number of half
lives passed, amount of starting material, and
amount of starting material present after a
given number of half-lives