element abundances
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8/10/2019 Element Abundances
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Familiar ways of classifying the elements
IA
IIA
IIIB
IVB
VB
VIB
VIIB VIIIB IB IIB
IIIA
IVA
VA
VIA
VIIA
Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I XeYRb Sr
Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At RnLaCs Ba
B C N O F NeLi Be
Al Si P S Cl Ar Na Mg
Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr ScK Ca
AcFr Ra
3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54
55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86
87 88 89
VIIIA
58 59 60 61 62 63 64 65 66 67 68 69 70 71
90 91 92 93 94 95 96 97 98 99 100 101 102 103 p e r i o d
H
1
2
3
4
56
7
1 He
2
metals
non-metals
semi-conductors
(semi-metals; metalloids)
IA IIA
IIIB
IVB
VB
VIB
VIIB VIIIB IB IIB
IIIA
IVA
VA
VIA
VIIA
VIIIA
Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I XeYRb Sr
Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At RnCs Ba
B C N O F NeLi Be
Al Si P S Cl Ar Na Mg
Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr ScK Ca
Fr Ra
3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54
55 5657-71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86
87 8889-103
HeH1 2
2
3
4
5
6
7
1
transition elements
Alternatively...
COSMIC ABUNDANCE of the ELEMENTS and NUCLEOSYNTHESIS February 3, 2005
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Geochemical variations on the periodic table...
IA
IIA
IIIB
IVB
VB
VIB
VIIB VIIIB IB IIB
IIIA
IVA
VA
VIA
VIIA
Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I XeYRb Sr
Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At RnLaCs Ba
B C N O F NeLi Be
Al Si P S Cl Ar Na Mg
Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr ScK Ca
AcFr Ra
3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54
55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86
87 88 89
VIIIA
58 59 60 61 62 63 64 65 66 67 68 69 70 71
90 91 92 93 94 95 96 97 98 99 100 101 102 103
H
1
2
3
4
5
6
7
1 He
2
ABUNDANCE
abundant in cosmos but not in(on) Earth
major elements in Earth (>1 wt%)~
trace elements (< 0.1%; some < 1 ppm)~
minor elements in Earth (0.1 < conc < 1%)~~
Al13
Ga31
400 atoms
10 atoms6
Si14
Ge32
118 atoms
10 atoms6
relative abundances of chemicallysimilar elements
SIZES OF ATOMS (IONIC RADII)
SbSnIn
AtPoTlHg
As
OLi Be B C
Na Mg Al Si
K Ca TiSc
Rb
Cs
Fr
Sr
Ba
Ra
Y
La
Ac
Zr
Hf
Th
V
Ta
Pa
Nb
Cr
Mo
W
U
Mn
Tc
Re
Fe Co
Os Ir Pt
RuRh Pd
NP
Au
PbBiCd
Ag
Ni GeGaZnCu
F
Cl
Br
I
S
Se
Te
Ionic radius increases coming out of the figure.Sizes apply to the valence state that is mostcommon in natural systems.
"Host" mineral
(made of majorelements)
Trace elementssubstitute into suit-able lattice sites
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IA
IIA
IIIB
IVB
VB
VIB
VIIB VIIIB IB IIB
IIIA
IVA
VA
VIA
VIIA
Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I XeYRb Sr
Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At RnLaCs Ba
B C N O F NeLi Be
Al Si P S Cl Ar Na Mg
Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr ScK Ca
AcFr Ra
3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54
55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86
87 88 89
VIIIA
58 59 60 61 62 63 64 65 66 67 68 69 70 71
90 91 92 93 94 95 96 97 98 99 100 101 102 103 p e
r i o d
H
1
2
3
4
5
6
7
1 He
2
highly volatile (atmophile)
moderately volatile
refractory
siderophile
These geochemical tendencies largelydetermine where in the Earth many
elements are sequestered – e.g.,siderophile elements are concentratedin the core; volatile elements werepartially lost from the Earth during itshot early history.
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Some general features of cosmic abundance curve
>75% of the mass of the universe is hydrogen>99% is H + He
(note: These statements do not apply to the Earth)
Elemental abundances drop off exponentially with increasing atomic number (Z)up to Z ~ 60; therafter remain ~constant
Li, Be & B show marked depletion relative to both higher and lower-Z elements
There is a pronounced abundance peak in the vicinity of Fe, as well as a few lessobvious peaks at higher Z
Even-Z elements are more abundant than their odd-Z neighbors
A Z N no. of stable isotopes
odd odd even 50
odd even odd 55
even odd odd 4
even even even 165!
COSMIC ABUNDANCES of the elements
atomic number, Z
10 20 30 40 50 60 70 80 90
H
He
Li
Be
B
C
Si Fe
Pb
Th
U l o g
r e l a t i v e a b u n d a n c e ( S
i = 1 0
) 6
1 0 0
-2
2
4
6
8
10rare earth elements:
"odd-even" effect
La
Lu
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l o g o f a
b u n d a n c e ( r e l a t i v e t o 1 0
S i a t o m s )
6
Z
cosmic abundances of the elements(Anders & Ebihara, 1982)
even Zodd Z
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similarilty in composition of chondrites and solar atmosphere...
Note: This diagram is a useful illustration, but bear in mind that:
1) it is a log-log plot ( and just about anything can appear to be linear on such a plot!)
2) the chondrites represented are actually metamorphic rocks, so their compositionmay not be "primitive" in all respects
O
MgFe
SNa Al
CaNi
Cr
MnP
CoK
Ti
ZnCu
GeScSr
BRb
BaY
Pb
Li
CeLa
BePr
ThTm
log relative abundance in C1 chondrites (Si = 10 )610
-2 0 2 4 6 8
l o g
r e l a t i v e a b u n d a n c e
i n s o l a r a t m o s p h e r e
( S i = 1 0
)
1 0
6
-2
0
2
4
6
8
*
* Chondrites are the most "primitive" of meteorites -- i.e., ones we believe representthe original, overall composition of the solar system. Five distinct types of chondritesare recognized.
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red numbers: number of solar masses
green numbers: time on main sequence
M A S E Q U
E ( b
r n n )
I N
E N C
H u i g
red
giants
whitedwarfswhite
w rfs
bluegiants
red dwarfs
SUN
22 Ma
68 Ma
232 Ma
1.6 Ga
9 Ga
9
5
3
1.5
4.4 4.2 4.0 3.8 3.6
0.1
1
10
100
1000
1E4
1E5
log surface temperature, K
l u m i n o s i t y r e l a t i v e t o S u n
Hertzsprung-Russell Diagram
He burning
"Burning" of hydrogen and helium in first-generation stars
First-generation stars are ones that have come together from an"original" hydrogen-helium cloud – that is, they do not represent "re-processed" stellar material from a previous supernova explosion (theSun is actually a second-generation star ). In first-generation stars,hydrogen "burning" to produce helium occurs by these reactions:
H11 H
11
+ H21 + energy
H21 H
11+ He
32 + energy
He32He
32
+ He42 H
11H
11
+ energy++
The elements as we know them are created in the interiors of stars...
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On the main sequence, helium is the main product of hydrogenburning. A gravitationally stable core of helium is produced in the star,and hydrogen burning continues on the surface of the core. As H-burning migrates outward, the luminosity of the star increases slightly:
If the star is massive enough to achieve the required temperature anddensity in the core, is initiated and heavier elementscan be synthesized
This process is exceedingly inefficient because is unstable and-16
decays with a half-life of only 10 s. What probably happens is thatanother helium nucleus is immediately absorbed to make a carbonnucleus:
or
helium burning
He42+He
42 Be
84
Be84
+Be84 He
42 C
126
+ He42 C
126He
42He
42
+
hydrogen burning
Note: These helium nuclei are actually positively-charged alphaparticles and repel each other strongly (remember Mr. Coulomb?).Extreme temperatures and pressures are required to get them tofuse: He burning can occur only in stars having masses of 80% ormore of our Sun. This "triple-alpha" process is the key tomaking heavier elements...
Hecore
H burning here
(endothermic!)
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He burning here
carboncore
carbon + someheavier elements
outer envelope super-heated; greatly expands
1 2 3 4
nuclear fuel exhausted; star collapses to white dwarf
5
helium burning
He burning sustains red giants
for a few 10s of Ma at most
Somewhat heavier elements...
If a red giant is sufficiently massive, successively heavier elements can besynthesized by addition of alpha particles (He nuclei) to carbon...
56 56This "alpha-process" can continue up to Ni (which decays to Fe), butelements heavier than Fe cannot be made by this process because the
repulsion between large, positively-charged nuclei and particles is too strong.
Note that the nuclei forming by this process are all even-Z. Smallerabundances of odd-Z nuclei are produced by reactions among the fusionproducts, such as:
+ He42C
126
16O8
16O
8
+ He4
2
20Ne
10etc.
+H
1
1C
12
6
23
Na11C
12
6 +
and16
O8+ 31
P1516
O8 H11+
This creates further possibilities, e.g...
and
+ H11C
126
13N7 + then
13N7
13C6
++
+
16O8
+ +13C6 He
42
nThis type of reaction iscrucial because neutrons area product! (more soon)
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Later generations of stars and the CNO cycle
That's about as much as we need to know about first-generation stars. The
key thing to remember is that when these explode, they contribute elementsheavier than H and He to the interstellar gas, so the next generation of stars canbegin with a different, more "versatile" fuel. Subsequent stars can burn hydrogenin the CNO cycle, in which hydrogen nuclei are added to carbon to produce firstnitrogen and then oxygen. This mode of H burning requires less extremeconditions than the proton-proton fusion reactions on p. 6. The Sun is nowburning H in the CNO cycle:
+ H11C
126
13N7
13N7
decaysC
136
C136 + H
11
14N7
15O8
decays 15N7
14N7 + H
11
15O8
He42
+15N7 + H
11 C
126
4 12end result: 4 protons fused to make He; C "released" for future use
H-burningHe-burning
C-burning
Ne-burningO-burning
Si-burning
H-burningunburned H
He-burning
unburned He
H-burning
unburned H
process fuel products temperature (K)
H-burningHe-burningC-burningNe-burningO-burningSi-burning
HHeCNeO
Mg to S
HeC, OO, Ne, Na, Mg
O, Mg
Mg to S
elements near Fe
6E72E88E815E82E93E9
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Z
N
N =
Z
" n d
o f t b
i l i y
b a
s a t "
Synthesis of heavy nuclei by neutron capture:the and in second-generation starss- r-processes
Elements heavier than Fe: NEUTRON CAPTURE
If there is a source of neutrons, the following type of reaction can occur
If a nucleus absorbs too many neutrons, it will eventually become too neutron-rich to be stable and decay by beta decay. Through neutron-capture reactions, itis possible to work up through most of the periodic table.
We recognize two distinct types of neutron-capture processes, which differ interms of the neutron flux required:
s-process: moderate neutron fluxes in the late red-giant stage
r-process: very high neutron fluxes in supernovae
A A+1 X + neutron = X z z
neutronnucleus new, heavier
nucleus
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Cd48
In49
Sn50
Sb51
62 63 64 65 66 67 68 69
70 71 72
73 74
s-process path
r-process
stableunstable tobeta decayN
Z
Creating heavy elements by neutron capture: An example...
Fe + n (stable)56
Fe57
Fe + n (stable)57
Fe58
Fe + n (t = 45 d)58
Fe59
½
The way things proceed from here depends upon the neutron flux (no. of
neutrons available). , the next step would be:If the flux is limited
Fe59 Co + e + 59
Co + n (t = 5 y)59
Co60
½
Co60 Ni + e + Ni is stable)60 60
However, (lots of neutrons available), we can get59 59
past Fe: instead of decaying to Co, it absorbs another neutron...if the neutron flux is large
Fe + n (t = 3E5 y)59 Fe60 ½
Fe + n (t = 6 m)60
Fe61
½
Co61 Ni + e + Ni is stable)61 61
Fe61 Co + e + (t =1.65 h)61
½
So...We got to adifferent placebecause wehad moreneutronsavailable
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N
Z
Fe
Co
Ni
Cu
Zn
Ga
56 57 58 59 60 61 62 63 64 65 66 67 68
68 69 70 71
71 72 73
63 64 65 66
60 61 62 63 64 65
70
69
59 60
64 65 66 67 68 69
r-process
s-process
n capture
decay
decay
Z
N
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SUMMARY
neutron capture
stellar fusion
spallation
Big Bang
atomic number
r e l a t i v e a
b u n d a n c e
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Neutron Activation: “artificial” nucleosynthesis
An example of neutron capture followed by beta decay (as in the s-process)...
Neutron activation is an analytical technique used extensively in the bio-,geo- and materials sciences for measurement of trace concentrations (e.g.1-100 ppm) of elements in a wide variety of materials. As the name suggests,it involves the use of a neutron flux in a research reactor to “activate” theelement of interest. This really means that the element (nucleus) of interestis “transmuted” -- by absorbing a neutron -- into a heavier nucleus that isradioactive. This “activated” nucleus is then detected by recording thegamma ray emitted when it disintegrates by beta decay.
The sequence just described (neutron absorption followed by beta-decay)is analogous to a step along the s-process path (see class hand-out). Theonly difference in the case of neutron activation is that the source of neutrons
is a man-made reactor (and the target nuclei are different).
Here’s an example: Analysis of SiO glass for sodium impurities...2
mostly SiO with2
a few Na atomsneutrons
23 24 23 24Na is “activated” by conversion to Na: Na + N Na
24 ( Na is radioactive)
Step 1 Place glass sample in reactor
24Step 2 Detect Na decay events by counting rays produced by the reaction
glass sample
detector
24 - 24Na ( , ) Mg
11
12
23 24
N
Z Na11
23Na11
24
Mg12
24
23“activation” of Na by neutron absorption
-decay(t = 15h)1/2
On the familiar Z-N diagram...
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