the genesis of the elements saliya ratnayaka for chem 510 october 22,2004
TRANSCRIPT
The Genesis of the Elements
Saliya RatnayakaSaliya Ratnayaka
For Chem 510For Chem 510
October 22,2004October 22,2004
Theories…?
How the universe was formed?How the universe was formed? How the various elements were formed?How the various elements were formed? Why the different elements and their Why the different elements and their
isotopes occur in the relative abundance we isotopes occur in the relative abundance we observe on earth?observe on earth?
Big Bang Theory
All the matter in the universe was packed as All the matter in the universe was packed as elementary particles into a “nucleus”elementary particles into a “nucleus”
This exploded!This exploded! Dispersed the matter uniformly as neutronsDispersed the matter uniformly as neutrons These neutrons then decayed These neutrons then decayed
epn 01
11
10
Big Bang Theory
Initially the temperature was 10Initially the temperature was 1066-10-1099 K K Number of nuclear reactions occurredNumber of nuclear reactions occurred
Once the temperature drops all these reactions stopOnce the temperature drops all these reactions stop
HenHe
HenHe
HeHH
HnH
52
10
42
42
10
32
32
11
21
21
10
11
88.6% H
11.3% He-------------------------------------------
99.9% of the atoms in the universe!
MAz
Z = atomic number
A = mass number
A Star is Born!
The Cosmic Perspective, J. Bennett et al, 2002, Pearson Education, Inc.,Publishing as Addison Wesley
Hertzsprung-Russell (H-R) diagram
A Star is Born!
Eagle NebulaHubble Space Telescope
Pleiades
The Cosmic Perspective, J. Bennett et al, 2002, Pearson Education, Inc.,Publishing as Addison Wesley
Synthesis of heavier elements
Stars are extremely dense (10Stars are extremely dense (1088 g cm g cm-3-3) and the ) and the temperature is about 10temperature is about 1077 K K
Nuclei can undergo nuclear fusion at these Nuclei can undergo nuclear fusion at these conditionsconditions
The first process in the synthesis is The first process in the synthesis is Hydrogen Hydrogen burningburning
A small amount of mass is lost and energy is A small amount of mass is lost and energy is evolved evolved (E = mc2)
More stable nuclei are formedMore stable nuclei are formed
Hydrogen Burning
DHH 21
11
11
2224 42
11 HeHOverall
HeHD 32
11
21
HHeHeHe 11
42
32
32 2
e01
Concise Inorganic Chemistry, 4th edition, J.D. Lee, Chapman & Hall Ltd
End of the Hydrogen burning Helium accumulates in Helium accumulates in
the corethe core The core begins to The core begins to
collapsecollapse H shell heats up and H H shell heats up and H
fusion begins there at a fusion begins there at a higher ratehigher rate
Gravity cannot balance Gravity cannot balance this pressurethis pressure
So the outer layers of the So the outer layers of the star expandstar expand
The star is now in the sub The star is now in the sub giant phase of its life giant phase of its life moving to the red giant moving to the red giant phasephase
The Cosmic Perspective, J. Bennett et al, 2002, Pearson Education, Inc.,Publishing as Addison Wesley
He Burning
MgHeNe
NeHeO
OHeC
CHeBe
2412
42
2010
2010
42
168
168
42
126
126
42
84
BeHeHe 84
42
42
The nucleus formed in this way fuse with more He
When the core collapsed and the temperature reached 108 K, He began to fuse
For a smaller mass star this cycle ends with C and become a white dwarf
Carbon-nitrogen Cycle
NHC 137
11
126
CN Decays 136
137
NHC 147
11
136
OHN 158
11
147
NO Decays 157
158
CHeHN 126
42
11
157
In larger stars (1.4 times the mass of the Sun or greater)
- Processes
CaHeAr
ArHeS
SHeSi
SiHeMg
4020
42
3618
3618
42
3216
3216
42
2814
2814
42
2412
In temperatures as high as 109 K
These fusion reactions happen up to 56Fe and are exothermic
The Iron (Fe) Problem The supergiant has an inert Fe core which collapses The supergiant has an inert Fe core which collapses
& heats& heats Fe can not fuseFe can not fuse It has the lowest mass per nuclear particle of It has the lowest mass per nuclear particle of
any elementany element It can not fuse into another element without It can not fuse into another element without
creatingcreating mass mass
The Cosmic Perspective, J. Bennett et al, 2002, Pearson Education, Inc.,Publishing as Addison Wesley
Supernova
Gravity makes Gravity makes electrons combine electrons combine with protons to form with protons to form neutrons, releasing neutrons, releasing neutrinos in the neutrinos in the processprocess
The Cosmic Perspective, J. Bennett et al, 2002, Pearson Education, Inc.,Publishing as Addison Wesley
Supernova
Crab Nebula in Taurussupernova exploded in 1054
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
The Cosmic Perspective, J. Bennett et al, 2002, Pearson Education, Inc.,Publishing as Addison Wesley
Evidence for the formation of heavier elements
Young stars have more Young stars have more heavy elements (2-3% heavy elements (2-3% mass) than old stars mass) than old stars (0.1%)(0.1%)
Even numbered nuclei Even numbered nuclei are relatively abundant are relatively abundant than nearest odd than nearest odd numbered nucleinumbered nuclei
Elements heavier than Elements heavier than iron are extremely rareiron are extremely rare
The Cosmic Perspective, J. Bennett et al, 2002, Pearson Education, Inc.,Publishing as Addison Wesley
References
1. Concise Inorganic Chemistry - 4th edition, Chapter 31 - by J.D. Lee 1. Concise Inorganic Chemistry - 4th edition, Chapter 31 - by J.D. Lee
2. Inorganic Chemistry - 3rd edition, chapter 1 - by D.F. Shriever, 2. Inorganic Chemistry - 3rd edition, chapter 1 - by D.F. Shriever, P.W. Atkins P.W. Atkins
3. Chemistry and Chemical reactivity - 4th edition, Chapter 24 - by 3. Chemistry and Chemical reactivity - 4th edition, Chapter 24 - by Kotz and Treichel Kotz and Treichel
4. The Cosmic perspective - 2nd edition, chapter 15- by J. Bennett, M. 4. The Cosmic perspective - 2nd edition, chapter 15- by J. Bennett, M. Donahue, N. Schneider, M. Voit Donahue, N. Schneider, M. Voit
5. Astrophysical Formulae -2nd edition, Pages 418-429, K. R. Lang 5. Astrophysical Formulae -2nd edition, Pages 418-429, K. R. Lang