PHYSICAL SCIENCE 1 – Formation of the Heavy Elements – Dapul
TOPIC / LESSON NAME
CONTENT STANDARDS
PERFORMANCE STANDARDS
LEARNING COMPETENCIES
SPECIFIC LEARNING OUTCOMES
TIME ALLOTMENT
We Are All Made of Star Stuff (Formation of the Heavy Elements)
The learners demonstrate an understanding of the formation of the elements during the Big Bang and
during stellar evolution.
The learners demonstrate an understanding of the distribution of the chemical elements and the
isotopes in the universe.
The learners can make a creative representation of the historical development of the atom or the
chemical element in a timeline.
1. Give evidence for and describe the formation of heavier elements during star formation and
evolution (S11/12PS-IIIa-2)
2. Write the nuclear fusion reactions that take place in stars, which lead to the formation of new
elements (S11/12PS-IIIa-3)
3. Describe how elements heavier than iron are formed (S11/12PS-IIIa-b-4)
At the end of the lesson, the learners will be able to:
1. Briefly discuss stellar nucleosynthesis or fusion
2. Discuss other processes that led to other elements
3. Write out fusion reactions involved
120 minutes ~ 2 hours
If the allotted subject time is 1 hour, it is recommended to end the first hour with #9.
LESSON OUTLINE:
1. Introduction/Review: Overview of the objectives and key terms, Review of the Big Bang and Big Bang nucleosynthesis
2. Motivation: Discussion of text The Cosmic Connection
3. Instruction/Delivery: Continuation of Big Bang into star formation, Discussion of star fusion processes, Discussion of other fusion
processes
4. Practice: Concept map, Alpha process practice
5. Enrichment: Brief discussion of man-made nuclei (presentation of performance task)
6. Evaluation: Question bank, Performance task to present one of the man-made elements
MATERIALS
RESOURCES
Projector, computer
Dhaliwal, J. K. (2012a). Nucleosynthesis: Alpha Fusion in Stars. [Powerpoint slides]. Retrieved from
http://earthref.org/SCC/lessons/2012/nucleosynthesis/
Dhaliwal, J. K. (2012b). Nucleosynthesis: Heavier Elements. [Powerpoint slides]. Retrieved from
http://earthref.org/SCC/lessons/2012/nucleosynthesis/
Nave, C. R. (2012). Nuclear fusion in stars. Retrieved
http://hyperphysics.phy-astr.gsu.edu/hbase/astro/astfus.html
September
23,
2015
from
PHYSICAL SCIENCE 1 – Formation of the Heavy Elements – Dapul
Penovich, K. (n.d.). Formation of the High Mass Elements. Retrieved September 23, 2015, from
http://aether.lbl.gov/www/tour/elements/stellar/stellar_a.html
Sagan, C. (2000). Chapter 26: The Cosmic Connection. In J. Agel (Ed.), Carl Sagan's Cosmic
Connection: An Extraterrestrial Perspective. Cambridge: Cambridge University Press.
Images:
Figure 1.
Equilibrium of the Sun [illustration]. (August 2007). Retrieved September 24, 2015 from
http://lasp.colorado.edu/education/outerplanets/solsys_star.php#nuclear
Figure 2.
Elert, G. (2015a). Proton-proton chain (main branch) [diagram]. Retrieved September 23, 2015, from
http://physics.info/nucleosynthesis/
Figure 3.
Commonwealth Scientific and Industrial Research Organisation (CSIRO). (2015). Hydrogen Shell
Burning on the Red Giant Branch [illustration]. Retrieved September 24, 2015 from
http://www.atnf.csiro.au/outreach//education/senior/astrophysics/stellarevolution_postmain.html
Figure 4.
Elert, G. (2015b). Triple alpha process [diagram]. Retrieved September 23, 2015, from
http://physics.info/nucleosynthesis/
Figure 5.
Elert, G. (2015c). Carbon nitrogen oxygen cycle [diagram]. Retrieved September 23, 2015, from
http://physics.info/nucleosynthesis/
PHYSICAL SCIENCE 1 – Formation of the Heavy Elements – Dapul
PROCEDURE
INTRODUCTION (5 MINUTES)
1.
Introduce the following learning objectives using any of the suggested protocols (Verbatim, Own
Words, Read-aloud)
a. I can give evidence for and describe the formation of heavier elements during star formation
and evolution.
b. I can write the nuclear fusion reactions that take place in stars, which lead to the formation of
new elements
c. I can describe how elements heavier than iron are formed
MEETING THE LEARNERS’ NEEDS
Teacher Tip:
1. Display the objectives and terms
prominently on one side of the classroom
and refer to them frequently during
discussion.
2.
2. To serve as an outline, you may map
out the lesson using the diagram in the
Practice portion of the lesson.
Introduce the list of important terms that learners will encounter:
a. fusion
b. stellar nucleosynthesis
c. proton-proton chain reaction d. triple alpha process
e. alpha ladder
f. CNO cycle
g. main-sequence star
h. red giant
i. supernova explosion
j. supernova nucleosynthesis
k. r-process
l. s-process
REVIEW (15 MINUTES)
3.
Review the stages of the Big Bang model, giving particular focus to nucleosynthesis and the
formation of light elements such as H and He. Discuss briefly that more significant amounts of Li, Be
and B formed through other processes, such as cosmic ray spallation. Remind them that once matter
had recombined, gravity and other forces acted to bring matter together, eventually forming stars 200 B
years after the Big Bang occurred.
4.
Remind
students
how
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symbols for an atom are written. Have
(!!!)
, or in terms of particle count, (!)𝑋 (!!!)
them
recall
3. Cosmic ray spallation is outside of the
lesson’s scope, but simply explain that
when particles in cosmic rays collide with
heavier elements they generate Li, Be
and B – among other elements –
through nuclear fission.
that
MOTIVATION (15 MINUTES)
5.
Briefly discuss the selection given as an assignment, Carl Sagan’s The Cosmic Connection.
Sagan found it remarkable that the elements we find on Earth are also those we find amongst the stars,
and that we find that most of what we know as matter was made by processes inside stars themselves.
Enrichment: Using the Think, Pair, Share protocol, ask students to reflect on the selection.
From their sharing, draw out one of the theses of the text: how being made of stardust makes
us both cosmic – we are as much a part of the universe as the stars – and yet helps us realize
that we are not the center of the universe.
Teacher Tip:
PHYSICAL SCIENCE 1 – Formation of the Heavy Elements – Dapul
INSTRUCTION/DELIVERY (55 MINUTES)
6.
Introduce that once hydrogen-helium
stars had formed from the action of gravity, the
hydrogen and helium atoms in stars began
combining in nuclear fusion reactions that
release a tremendous amount of light, heat, and
radioactive energy. Fusion resulted in the
formation of nuclei of new elements, so these
reactions inside stars are known as stellar
nucleosynthesis.
Emphasize that the first fusion process occurs in
the hydrogen core of stars with a temperature of
less than 15 million K, such as the Sun. These
kinds of stars are called main-sequence stars.
Discuss the three steps of the process known as
Figure 1. Equilibrium of the Sun and other mainthe main-branch proton-proton chain.
sequence stars. (Equilibrium of the Sun, 2007).
Deuterium (D or 2H) forms from proton fusion, with
one proton turning into a neutron via beta-plus
decay, giving off a neutrino and a positron:
1
H + 1H → 2H + ν + e +
3
He forms from deuterium and proton fusion, also
known as deuterium burning. This immediately
consumes all deuterium produced.
2
H + 1H → 3He + γ
4
He formation from 3He fusion.
3
He + 3He → 4He + 2 1H
The entire three-step process releases about 26.7
MeV (megaelectronvolts) of energy. Emphasize
that the energy released is responsible for the
thermal pressure that pushes against gravity, and
for the light, heat and radiation emitted by the star.
Add that a different process facilitates hydrogen
fusion in main-sequence stars with temp. greater
than 15 million K.
Figure 2. The main branch of the proton-proton
chain reaction (p-p chain) resulting in the
formation of 4He. (Elert, 2015a).
Teacher Tip:
6. You may emphasize the rates of
reaction in the proton-proton (p-p) chain,
and point out that it will likely take a
billion years before a specific proton is
involved in a successful p-p fusion. 2He
often immediately decays back into two
protons, and rarely is a proton converted
into a neutron to form deuterium (betaplus decay). However, with billions of
protons reacting, enough make it to the
next step.
After discussing each of the steps, ask
students to give the balanced equation
for the formation of one 4He atom in the
proton-proton chain. The answer is as
follows:
4 1H → 4He + 2 ν + 2 e+
PHYSICAL SCIENCE 1 – Formation of the Heavy Elements – Dapul
7.
Discuss how, as H is depleted, the core of
a star becomes comprised of He instead, while H
fusion only occurs in a shell around it. Due to this
process, the temperature and density of the core
of the star increases, up to 100 million K, and the
star’s thermal pressure causes it to push out H
gas. The star balloons into a red giant.
Figure 3. A star with a very dense helium core
and a hydrogen shell expands into a red giant
due to increased radiation pressure. (CSIRO,
2015)
Figure 4. The triple alpha process resulting in the
formation of 12C. (Elert, 2015b)
Several nuclear fusion processes occur in a red
giant aside from hydrogen fusion, the first of which
is the triple alpha process. Alpha particles refer
to 4He, so this reaction involves the fusion of three
4
He atoms in the following steps:
4
He + 4He → 8Be
8
Be + 4He → 12C + γ
Note that the 8Be intermediate is unstable, so
either it decays or forms 12C.
As it accumulates mass, the star can keep
growing into a supergiant, where alpha fusion
processes continue in the core via the alpha
ladder. More and more alpha particles are fused
to create heavier elements all the way until iron,
making the core and star itself more massive.
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7. Don’t give the complete alpha ladder.
Show only the ladder until neon. Later on
in Practice, ask students to write out the
complete the alpha ladder.
PHYSICAL SCIENCE 1 – Formation of the Heavy Elements – Dapul
8.
Mention that once carbon was
present from alpha processes, mainsequence stars hotter than 15 million K
could facilitate the production of helium
through a process where 12C is used as a
catalyst: the carbon fusion cycle or the
CNO cycle. Go through the cycle briefly,
demonstrating that this process involves
repeated proton capture and beta-plus
decay.
Figure 5. The CNO cycle, which uses 12C as a catalyst to
form more 4He in larger or hotter main-sequence stars.
(Elert, 2015c)
9.
Finally, share how due to the formation of heavier elements, a star will eventually be unable to
generate energy to push against gravity, causing it to collapse on itself. It then undergoes a supernova
explosion. Discuss that this releases a tremendous amount of energy, enough to synthesize elements
heavier than iron, including some of the heaviest elements known (uranium, thorium). This is done
through the r-process, which involves rapid capture of neutrons by the atom. Mention that other heavy
elements are also synthesized through s-process, which involves slow neutron capture in red giants.
PRACTICE (30 MINUTES)
10.
Review the lesson using the
following concept map. Give the map
with blanks in place of most of the
terms, and ask students to fill the
diagram in.
Figure 6. Concept map for the current lesson.
8. It is good to teach this in a way that
accounts for the number of protons and
neutrons in each step:
p+
n
Next step:
12
C
6
6
Add a proton
13
N
7
6
Convert a proton
13
C
6
7
Add a proton
14
N
7
7
Add a proton
15
O
8
7
Convert a proton
15
N
7
8
Add a proton
12
C
6
6
4
He 2
2
9. r-process and s-process need not be
discussed at length, but it will help to
mention that these processes change
the atom’s atomic weight, after which the
atom
undergoes
various
decay
processes to change its identity.
Teacher Tip:
10. Alternately, this concept map may be
used at the start of the lesson to guide
students with all the terms.
PHYSICAL SCIENCE 1 – Formation of the Heavy Elements – Dapul
11.
Using a provided periodic table, allow students to write out all the equations involved in the alpha
ladder. What do they notice about the atomic number patterns of the elements found in the ladder?
Explain that this feature of the alpha ladder, as well as other rules of stability, results in the oddnumbered elements being generally less abundant than the even-numbered elements beside them on
the periodic table. Emphasize that many other processes allowed for the odd-numbered elements,
including supernova nucleosynthesis, radioactive decay, electron and neutron capture, nuclear fission,
and cosmic ray spallation.
11. Students should notice that mostly
even-numbered
elements
emerge
through the alpha ladder, and that other
elements between carbon and iron need
to be accounted for in other ways.
ENRICHMENT (10 MINUTES & OUTSIDE OF CLASS)
12.
Mention that quite a few elements were first discovered as man-made elements, as many of
them were not found to emerge from the major nucleosynthesis reactions (or their minor processes).
These include elements Americium through Lawrencium, and also include some of the newer, recently
discovered elements (eg. Flerovium, Livermorium). Inform students that they will have to research on
one of these elements for the Performance Task.
Teacher Tip:
EVALUATION (20 MINUTES)
A.
Question Bank (sample questions for Written Evaluation)
Teacher Tip:
A. Correct answers:
1. b. r-process
1.
2.
Which of the following processes is likely to generate the heaviest element?
a. CNO cycle
c. triple-alpha process
b. r-process
d. Big Bang nucleosynthesis
Which of the following reactions is not a part of the alpha ladder?
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d. !!
!!𝑇𝑖 + !𝐻𝑒 → !"𝐶𝑟
!"𝑃 + !𝐻𝑒 → !"𝐶𝑙
3.
If an element is used up by a star in fusion, it is sometimes called “burning”, even though no
actual combustion occurs. Which of the following processes is likely to involve “carbon burning”?
a. alpha ladder
c. triple-alpha process
b. CNO cycle
d. s-process
4.
Modified True or False: If the statement is true, write True. Else, replace the underlined portion
with the correct word or phrase.
a. A star gets lighter as time goes on.
b. Most of the heaviest elements were formed in main-sequence stars.
c. The heavy elements in a star are found in its core.
2.
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!"𝐶𝑙
3. a. alpha ladder (CNO cycle does not
consume any carbon; it simply uses
carbon as a catalyst)
4.
a. heavier
b. supernova
c. True
d. True
B. Emphasize the importance of proper
research skills and citation throughout
the task, even with creative outputs. If
there is no time to present in class, they
may present outside of class directly to
you, or submit in a form that can be
viewed separately.
PHYSICAL SCIENCE 1 – Formation of the Heavy Elements – Dapul
d. In stellar nucleosynthesis, heavier elements are formed from combining lighter ones.
B.
Performance Task
Students will create an output that discusses the origin of one of the man-made elements. In their
output, they must:
• discuss the element’s basic characteristics
• give a brief timeline leading up to the element’s discovery
Students may present their research in the form of a poster, powerpoint,
infographic. A sample rubric may be given as follows:
1 pt.
3 pts.
Presentation of the Most
basic Basic aspects of the
element’s
characteristics of the element that can be
characteristics
element are missing or found on the periodic
absent
table are present
Timeline
of
the There is no clear chain
element’s discovery
of events or key
moments presented
(add creative metric)
(add other metrics)
The scientific history of
the
element’s
discovery was made
clear,
including
notable people and
groups involved
a report or essay, video, or
5 pts.
Unique aspects of the
element, for example
the element’s potential
significance or uses,
were presented
The element’s history
was presented clearly
and the process of
creating the element
was discussed