The Genesis of the Elements

1. The Genesis of the Elements Saliya Ratnayaka For Chem 510 October 22,2004

2. Theories…? • How the universe was formed? • How the various elements were formed? • Why the different elements and their isotopes occur in the relative abundance we observe on earth?

3. Big Bang Theory • All the matter in the universe was packed as elementary particles into a “nucleus” • This exploded! • Dispersed the matter uniformly as neutrons • These neutrons then decayed

4. Initially the temperature was 106-109 K Number of nuclear reactions occurred Once the temperature drops all these reactions stop Z = atomic number A = mass number Big Bang Theory 88.6% H 11.3% He ------------------------------------------- 99.9% of the atoms in the universe!

5. A Star is Born! Hertzsprung-Russell (H-R) diagram The Cosmic Perspective, J. Bennett et al, 2002, Pearson Education, Inc.,Publishing as Addison Wesley

6. A Star is Born! Eagle Nebula Hubble Space Telescope Pleiades The Cosmic Perspective, J. Bennett et al, 2002, Pearson Education, Inc.,Publishing as Addison Wesley

7. Synthesis of heavier elements • Stars are extremely dense (108 g cm-3) and the temperature is about 107 K • Nuclei can undergo nuclear fusion at these conditions • The first process in the synthesis is Hydrogen burning • A small amount of mass is lost and energy is evolved (E = mc2) • More stable nuclei are formed

8. Hydrogen Burning Concise Inorganic Chemistry, 4th edition, J.D. Lee, Chapman & Hall Ltd

9. The Cosmic Perspective, J. Bennett et al, 2002, Pearson Education, Inc.,Publishing as Addison Wesley End of the Hydrogen burning • Helium accumulates in the core • The core begins to collapse • H shell heats up and H fusion begins there at a higher rate • Gravity cannot balance this pressure • So the outer layers of the star expand • The star is now in the sub giant phase of its life moving to the red giant phase

10. He Burning When the core collapsed and the temperature reached 108 K, He began to fuse The nucleus formed in this way fuse with more He For a smaller mass star this cycle ends with C and become a white dwarf

11. Carbon-nitrogen Cycle In larger stars (1.4 times the mass of the Sun or greater)

12. - Processes In temperatures as high as 109 K These fusion reactions happen up to 56Fe and are exothermic

13. The Iron (Fe) Problem • The supergiant has an inert Fe core which collapses & heats • Fe can not fuse • It has the lowest mass per nuclear particle of any element • It can not fuse into another element without creating mass The Cosmic Perspective, J. Bennett et al, 2002, Pearson Education, Inc.,Publishing as Addison Wesley

14. Supernova • Gravity makes electrons combine with protons to form neutrons, releasing neutrinos in the process The Cosmic Perspective, J. Bennett et al, 2002, Pearson Education, Inc.,Publishing as Addison Wesley

15. Supernova The amount of energy released is so great, that most of the elements heavier than Fe are instantly created In the last millennium, four supernovae have been observed in our part of the Milky Way Galaxy: in 1006, 1054, 1572, & 1604 Crab Nebula in Taurus supernova exploded in 1054 The Cosmic Perspective, J. Bennett et al, 2002, Pearson Education, Inc.,Publishing as Addison Wesley

16. Evidence for the formation of heavier elements • Young stars have more heavy elements (2-3% mass) than old stars (0.1%) • Even numbered nuclei are relatively abundant than nearest odd numbered nuclei • Elements heavier than iron are extremely rare The Cosmic Perspective, J. Bennett et al, 2002, Pearson Education, Inc.,Publishing as Addison Wesley

17. References • 1. Concise Inorganic Chemistry - 4th edition, Chapter 31 - by J.D. Lee 2. Inorganic Chemistry - 3rd edition, chapter 1 - by D.F. Shriever, P.W. Atkins 3. Chemistry and Chemical reactivity - 4th edition, Chapter 24 - by Kotz and Treichel 4. The Cosmic perspective - 2nd edition, chapter 15- by J. Bennett, M. Donahue, N. Schneider, M. Voit 5. Astrophysical Formulae -2nd edition, Pages 418-429, K. R. Lang