Chemical Formation of the Earth

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Chemical Formation of the Earth

1. Cloud of elements condenses into planets
2. As they do so, they react to form compounds
3. They differentiate chemically and by density

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Chemical Makeup of the Earth
Two questions to answer Why are there unreacted
metals? Why are the metals in the core?
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Primary Differentiation of the Earth

• The biggest redox reaction in the world
• metals nonmetals ? compounds
• Focus on metals and nonmetals
• Metal elements that loses electrons
• Nonmetals elements that gain electrons

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Chemical Makeup of the Earth

• Bulk Earth
• Fe 35.4
• Mg 17.0
• Si 12.6
• Ni 2.7
• Ca 0.6
• Al 0.44
• O 27.8
• S 2.7
• All others 3.5

Element mass in Earth (g) molar mass mol element charge mol electrons
Fe 35.4 2.11338E27 55.85 3.78403E25 2 7.56806E25
Mg 17 1.0149E27 24.305 4.17568E25 2 8.35137E25
Si 12.6 7.5222E26 28.09 2.67789E25 4 1.07116E26
Ni 2.7 1.6119E26 58.69 2.74646E24 2 5.49293E24
Ca 0.6 3.582E25 40.08 8.93713E23 2 1.78743E24
Al 0.44 2.6268E25 26.98 9.7361E23 3 2.92083E24
Sum of electrons Sum of electrons 2.76511E26


O 27.8 1.65966E27 16 1.03729E26 -2 -2.0746E26
S 2.7 1.6119E26 32.07 5.02619E24 -2 -1.0052E25
Sum of electrons Sum of electrons -2.1751E26
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1. So, we end up with excess iron.2. It stays
in the metallic state and is dense, so it sinks
to the center of the earth, forming the metallic
core.3. Next question what other elements go
with Fe to the core? Which do not?
Primary Differentiation of the Earth
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Reaction potential Eoreaction Eored(cathode)
- Eo(anode) that is, Eored (species
reduced) - Eored (species oxidized) If
Eoreaction is positive, the reaction is favored.
If Fe can reduce a cation of the other
element to its neutral state, that element goes
to the core.
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Example Nickel Is the following reaction
favored? Fe ? Fe2 2 e- Eored
0.43 V Ni2 2 e- ? Ni Eored
0.25 V Eored 0.25 V (-0.43 V)
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Deficient Elements log(cosmic/crust)

• H 6.58
• He 14.17
• C 3.22
• N 5.25
• Ne 10.46
• Compare to O 0.79

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