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 describe the formation of heavier elements during star formation formation and evolution (S11/12PS-IIIa-2) 2. Write the nuclear fusion reactions reactions that take place in stars, stars, which lead to the formation of new elements (S11/12PS-IIIa-3) (S11/12PS-IIIa-3) 3. Describe how elements elements heavier than iron iron are formed (S11/12PS-IIIa-b(S11/12PS-IIIa-b-4) 4) At the en d of the le sson, the learners will be able to: 1. Briefly discuss stellar nucleosynth esis or fusion 2. Discuss other other processes processes that led to to other elements 3. Write out fusion reactions 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 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 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 Stars. [Powerpoint slides]. Retrieved from http://earthref.org/SCC http://eart href.org/SCC/lessons/2012 /lessons/2012/nucleosynthes /nucleosynthesis/ is/ Dhaliwal, J. K. (2012b). Nucleosynthesis: Heavier Elements. Elements. [Powerpoint slides]. Retrieved from http://earthref.org/SCC http://eart href.org/SCC/lessons/2012 /lessons/2012/nucleosynthes /nucleosynthesis/ is/ Nave, C. R. (2012). Nuclear fusion in stars. Retrieved http://hyperphysics.phyhttp://hyperph ysics.phy-astr.gsu.edu/ astr.gsu.edu/hbase/astro/as hbase/astro/astfus.html tfus.html
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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. Perspective. Cambridge: Cambridge University Press. Images: Figure 1. Equilibrium of the Sun Sun [illustration]. [illustration]. (August 2007). Retrieved September 24, 2015 from http://lasp.colorado.edu/ http://las p.colorado.edu/education/outer education/outerplanets/sols planets/solsys_star.php#n ys_star.php#nuclear uclear Figure 2. Elert, G. (2015a). Proton-proton chain (main branch) [diagram]. 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 Branch [illustration]. Retrieved September 24, 2015 from http://www.atnf.csir http://www .atnf.csiro.au/outreach/ o.au/outreach//education/seni /education/senior/astrophy or/astrophysics/stel sics/stellarevolut larevolution_postmain.html ion_postmain.html Figure 4. Elert, G. (2015b). Triple alpha process process [diagram]. http://physics.info/nucleosynthesis/
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Figure 5. Elert, G. (2015c). Carbon nitrogen oxygen cycle 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 following learning objectives using any of the suggested protocols (Verbatim, Own Words, Read-aloud) a. I can give evidence for and describe the formation formation of heavier elements elements during star formation formation and evolution. b. I can write the nuclear fusion reactions reactions that take place in stars, stars, which lead to the formation formation of new elements c. I can describe describe how elements heavier than iron are formed 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 nucleosynth esis c. proton-proton 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 nucleosynthesis k. r-process l. s-process
REVIEW (15 M INUTES) 3. Review the stages of the Big Bang model, giving particular focus to nucleosynthesis 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. 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.
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MOTIVATION (15 MINUTES) Teacher Tip: 5. Briefly discuss the selection given as an assignment, Carl Sagan’s The Cosmic Connection. 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.
PHYSICAL SCIENCE 1 – Formation of the Heavy Elements – Dapul INSTRUCTION/DELIVERY (55 MINUTES) 6. Introduce that once hydrogen-helium hydrogen-helium stars had formed from the action of gravity, the hydrogen and helium atoms in stars began combining in nuclear fusion 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. 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 main-sequence stars. stars. Discuss the three steps of the process known as the main-branch proton-proton chain. chain .
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 (beta(beta plus decay ). ). However, with billions of protons reacting, enough make it to the next step.
Figure 1. Equilibrium of the Sun and other mainsequence stars. (Equilibri (Equilibrium um of the Sun, 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 2 H + 1H H + ! + e+ 3 He forms from deuterium and proton fusion, also known as deuterium burning . This immediately consumes all deuterium produced. 2 3 H + 1H He + " 4 3 He formation from He fusion. He + He He + 2 H The entire three-step process releases about 26.7 MeV (megaelectronvolts) of energy. Emphasize Figure 2. The main branch of the proton-proton that the energy released is responsible for the chain reaction (p-p chain) resulting in the 4 thermal pressure that pushes against gravity, and formation of He. (Elert, 2015a). 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. !
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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 4 1H He + 2 ! + 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. 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)
Several nuclear fusion processes occur in a red giant aside from hydrogen fusion, the first of which is the triple alpha process. process. Alpha particles refer to 4He, so this reaction involves the fusion of three 4 He atoms in the following steps: 4 8 He + 4He Be 8 4 12 Be + He C + " Note that the 8Be intermediate is unstable, so either it decays or forms 12C. !
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As it accumulat es 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. cycle. Go through the cycle briefly, demonstrating that this process involves repeated proton capture 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 to the formation of heavier elements, a star star will will eventually be unable unable to to generate energy to push against gravity, causing it to collapse on itself. It then undergoes a supernova explosion. 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, r-process, which involves rapid capture capture of neutrons by the atom. Mention that other heavy elements are also synthesized through s-process, s-process, which involves slow neutron 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 N 7 6 Convert a proton C 6 7 Add a proton 14 N 7 7 Add a proton 15 O 8 7 Convert a proton N 7 8 Add a proton 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 provided periodic periodic table, allow students to write write out all the equations equations involved 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, 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) Teacher Tip: 12. Mention that quite quite a few elements were first discovered as man-made man-made elements, 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. EVALUATION (20 MINUTES) A. Question B ank (sample questions for Written E valuation) 1.
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3. If an element element is used up by a star star in fusion, it is sometimes called “burning”, even though no actual combustion occurs. Which of the following processes processes is likely to involve “carbon burning”? a. alpha ladder c. triple-alpha process b. CNO cycle d. s-process B. Emphasize the importance of proper research skills and citation throughout 4. Modified True or False: If the statement is true, write True. Else, replace the underlined portion the task, even with creative outputs. If with the correct word or phrase. there is no time to present in class, they a. A star gets lighter as time goes on. may present outside of class directly to b. Most of the heaviest elements were formed in main-sequence stars. stars. you, or submit in a form that can be c. The heavy elements in a star are found in its core. 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 timeline leading up to the element’s element’s discovery discovery • •
Students may present their research in the form of a poster, powerpoint, a report or essay, video, or infographic. A sample rubric may be given as follows: 1 pt. 3 pts. 5 pts. Presentation of the Most basic Basic aspects of the Unique aspects of the element’s characteristics of the element that can be element, for example characteristics element are missing or found on the periodic the element’s potential absent table are present significance or uses, were presented Timeline of the There is no clear chain The scientific history of The element’s history element’s discovery of events or key the element’s was presented clearly moments presented discovery was made and the process of clear, including creating the element notable people and was discussed groups involved (add creative metric) (add other metrics)
