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Thematic Questions about Chemical Elements• Nature of the chemical elements
•What distinguishes elements from one another?• Occurrence of the range of elements
•Which elements occur in the universe and why?• Origin of specific elements
•How, why and when were the various elementsformed?
• Stability of individual elements•Why are some elements unstable?•What happens to them?
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Element Synthesis: Exploration ofChemical Fundamentals
Element Synthesis and Isotopes• Elemental Abundance and Isotopes
•distribution of elements in the universe•factors that define elemental differences
• Forms of Radioactivity•types of decay and processes
• Formation of Elements and their Stability•sequence of element formation in stars•role of binding in stabilizing atomic nucleii
• Elemental Composition of the Universe•products of formation and nuclear fusion
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Element Building: Nucleosynthesis
2
hydrogen
10 20 30 40 50 60 70 80 90Element (Atomic ) Number
10-2
100
102
104
106
108
1010helium
beryllium
oxygen
silicon iron
boron
leadbismuth
thorium uranium
Relative
abu
ndan
ce (Si
= 1
06)
Relative Abundance in the Sun• non-uniform trend
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Cosmic Abundance of Elements
•general decrease as atomicnumber increases; even > odd
•higher relative abundance ofiron and lead
•production or preservation?
Elemental Characteristics• Major components: protons, neutrons, electrons• Atomic Number = number of protons in nucleus• Name: Helium; Symbol: 3He2
• 2 = atomic number, which determines name• 3 = sum of protons and neutrons
• Elements may have variable numbers ofneutrons: 3He2 or 4He2; these are isotopes
• Individual isotopes may be stable or unstable• unstable = radioactive, decay to other elements• elements without stable isotopes don’t occur naturally
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Elements and Isotopes
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Examples of Characteristics• Names, symbols, isotopes (radioactive)
•Most elements occur as a number of isotopes
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Simplest Elements
Name Hydrogen Helium Lithium BerylliumSymbol H He Li BeAtomic No. 1 2 3 4Isotopes 1,2,3 3,4 6,7 9,10
Name Boron Carbon Nitrogen OxygenSymbol B C N OAtomic No. 5 6 7 8Isotopes 10,11 12,13,14 14,15 16,17,18
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Natural Distribution of Isotopes
Equal numbers ofprotons andneutrons
10 20 30 40 50 60 70 80 90Number of Neutrons
0
10
20
30
40
50
60
Natural trend ofelements, more
neutrons than protons
Num
bers
of
Prot
ons
100 110 120
70
80
4
Three Common Forms of Radioactive Decay• Nucleons constant, but changed in alpha decay
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Radioactivity
Beta decay
14N
14C
7
6
7 8
14C e- + 14N(n° e- + p+)
No. neutrons
No.
pro
tons
Electron capture
40K
40Ar
19
18
21 22
40K + e- 40Ar(p+ + e- n°)
No. neutrons
No.
pro
tons
Alpha decay 238U92
91
144 146
238U 234Th + 4He
No. neutrons
No.
pro
tons
90 234Th
145
Fusion Processes• Formation of Deuterium (2H1)
•subsequent focus on protons and neutrons
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Formation of Elements
positron
neutrino
1H1
1H12H1
proton
neutron
nucleons
5
Initial Stages of Fusion
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Formation of Elements
1H1
1H1
2H1
1H13He2
3He2
4He2
+
2 x 1H1
2 x 4He2
8Be412C6
4He24He2
4He2
16O8 20Ne10
1. hydrogen burning to helium (to 6 x 107K)
2. successive burning of He, C, O, and Ne (to 1.5 x 109K)
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4He2
16O8 20Ne10
3. Capture of 4He (α-particles; T = 109K)
4He24He2
24Mg1228Si14
28Si14 4He2 4He24He2
32S1636Ar18
40Ca20
Subsequent Stages of Fusion
Formation of Elements
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4. An equilibrium process that accounts for the highabundance of iron group elements (T = 4 x 109K)
5. Neutron capture by the slow (s) process with long time (102 - 105 years) intervals between successive captures allowing for intervening β decay
6. Neutron capture by the rapid (r) process in supernovawith short (0.01s - 1s) intervals between successive captures, enabling formation of elementsbeyond bismuth
Later Stages of Nucleosynthesis
Formation of Elements
not made by s-processmade by s-processradioisotopes along s-path
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• Slow process with the cores of stars (nuclear reactor)• Rapid process occurs during supernova (atomic bomb)
Comparison of Neutron Capture Processes
Formation of Elements
Se 34As 33Ge 32Ga 31Zn 30Cu 29Ni 28Co 27Fe 26
30 31 32 33
3734 35 36
41
neutrons
42 43
38 39 40
elem
ent/
prot
ons
s-processneutron captureelectron capturelater β-decay
elem
ent/
prot
ons
neutrons48 49 50 51 52
Mo 42Nb 41Zr 40Y 39Sr 38Rb 37Kr 36Br 35Se 34As 33Ge 32Ga 31
53 54 55 56
r-processneutron captureβ-decaylater β-decay
not made by r-processmade by r-processradioisotopes along r-path
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7. Proton capture (p-process) yielding rare light isotopesof heavy elements in an H-rich medium (T = 3 x 109K)
Final Process of Nucleosynthesis
Formation of Elements
Controls on Nucleosynthesis• Relationship to stability of nuclei
•binding energies of nucleons vs. atomic number•even numbers of nucleons more tightly bound
Occurrence of Nucleosynthesis• Nuclear fusion within stars, supernova
•related to star size
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4He2
16O8
20Ne10
24Mg12
28Si14 56Fe26
12C6
Most Stable Nucleii• Isotopes with low
binding energies•Matches cosmicabundance of majorelements (9/top 10)
Stability of the Elements
H He C (N) O% 77 21 0.3 (0.5) 0.8
Ne Mg Si S Fe% 0.2 0.06 0.07 0.04 0.1
32S16
1H1
8
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Stability• Low binding
energiesare morestable
• A functionof packingof nucleonswithinnucleus
Binding Energy of Atomic Nuclei
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Nucleon Number Systematics
Odd vs. Even• Smaller nuclear
mass is morestable
• Even numbersof nucleonspack tighterwithin nucleus
• Even numberednuclei are morestable Proton Number
42 43 44 45 46 47 48
60 59 58 57 56 55 54Neutron Number
O-OO-O
O-O
E-EE-E
Mass 102isobar
Neutron Number
42 43 44 45 46 47 48
61 60 59 58 57 56 55
E-O
E-O
E-OO-E
O-E
Mass 103isobar
Proton Number
Incr
easing
Mas
s
9
Dependent on Size and Temperature• Element burning from interior outward• Series of layers
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Element Formation within Stars
H-burning
He-burning
C-burning
Ne-burning
O-burning
Si-burning
H-burning
unburned H
He-burning
unburned He
The Sun Late Sun Large star as Red Giant
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Summary of Processes• Big bang formation of
atomic matter (H, He)• Sequential series of
nucleosyntheticprocesses within starsand supernova
• Resulting cosmicoccurrence of elements• function of synthesis
and stability
Abundance of Elements