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Comprehensive Exams > Stable Isotopes > Flashcards

Stable Isotopes Flashcards

1
Q

Delta Notation

A
  • Means of expressing the relative abundance of the heavier stable isotope in a mixture of atoms
  • units are per mil
d = (Rsample/Rstandard-1)*1000
R = molar ratio of heavy-to-light isotope (ex: 13C/12C)
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2
Q

Founding Fathers of Isotope Ecology

A

Tom Hoering (Carnegie), Harmon Craig (Scripps), Harold Urey (U of Chicago), Sam Epstein (Caltech)

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3
Q

Hutchinson’s ecological niche

A

n-dimensional set of points in a space whose axes represent environmental variables

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4
Q

Electron

A

tiny subatomic particle with negative charge

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5
Q

proton

A

subatomic particle with a positive charge

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6
Q

Neutron

A

Subatomic particle with no charge. Similar mass to protons

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7
Q

Atomic Number (Z)

A

Integer that expresses the number of protons in the nucleus

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8
Q

Mass Number (A)

A

The sum of protons and neutrons in a nucleus

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9
Q

Atomic Mass

A

The mass of a neutral, noncharged, atom of a nuclide

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10
Q

Atomic Mass Unit (AMU)

A

A measure of atomic mass

1 AMU = 1/12 mass of 12C

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11
Q

Radioactive Decay

A

Decay of an element to a different form with a more stable energy configuration

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12
Q

Half-Life

A

Time required for one half of the atoms in a sample of a radioactive isotope to decay

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13
Q

Isotopes

A

Atoms which have the same number of protons in their nuclei, but different numbers of neutrons

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14
Q

Isotopologues

A

Isotopic species of the same molecule

Carbon dioxide has 12 isotopologues: 12C16O16O, 12C16O17O, etc

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15
Q

Isotopomers

A

Isotopologues that differ from one another only in the position of the isotopic elements

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16
Q

International Reference Standard for Hydrogen

A

V-SMOW, Vienna Standard Mean Ocean Water

17
Q

International Reference Standard for Oxygen

A

V-SMOW, Vienna Standard Mean Ocean Water

V-PDB, Vienna Pee Dee Belemnite

18
Q

International Reference Standard for Carbon

A

V-PDB, Vienna Pee Dee Belemnite

19
Q

International Reference Standard for Nitrogen

A

Air, Atmospheric Air

20
Q

Fractionation

A

Isotopic separation/sorting

Isotopes of the same element undergo the same chemical reactions because they have the same protons and electrons. Isotopes have different thermodynamic properties due to their different masses (melting point, vapor pressure, diffusion coefficient, and equilibrium and kinetic rate constants). Thus, different isotopes react at different rates in chemical reactions, which leads to fractionation.

21
Q

Results of fractionation

A

abundance of heavy isotopes in the reactant being different from the abundance of heavy isotopes in the product

lighter goes faster

22
Q

Isotopic fractionation factor (alpha)

A

alpha = (1000 +delta of reactant)/(1000+delta of product)

23
Q

Exchange - Equilibrium Fractionation

A
  • equilibrium
  • complete back-reactions occur
  • product/reactant offset by constant fractionation factor
  • physical state changes (water to vapor)
  • chemical transformations (carbonic acid to carbon dioxide and water)

ex: liquid droplet formation from vapor in clouds, evaporation at the boundary layer (100% RH) of body of water

24
Q

Transport/Diffusive Fractionation

A
  • non-equilibrium
  • kinetic fractionation dealing with flux rather than chemical reaction
  • incomplete back-flux is the rule

ex: diffusion through boundary layer over water, out of leaves, through soils

25
Q

Kinetic Fractionation

A
  • non equilibrium
  • incomplete back reactions or none occur
  • product and reactant delta values can evolve in concert (closed system) or product composition determines reactant composition (open system)

ex: biosynthesis (enzyme mediated), evaporation of water (<100% RH)

26
Q

Temperature effect on equilibrium fractionation

A

alpha approaches zero (less fractionation) at higher temperatures

27
Q

Rayleigh Distillation/Fractionation

A

Evaporation - vapor is formed from the liquid and the fraction remaining of original liquid declines

Can also describe the process as vapor mass condenses (rainfall)

28
Q

Kinetic Reactions

A

Forward reaction rate is accelerated relative to backward reaction and opportunity for backward mixing diminishes.

Ratio of reaction rate constants (k) determine fractionation

Most biological (enzyme) reactions

29
Q

5 Water World Rules to Remember

A
  1. expect fractionation during phase changes (liquid to vapor)
  2. temperature will impact isotopic composition (lower temps = larger isotopic affects)
  3. Isotope composition of any water is a result of fractionation, mixing, or both
  4. Always anticipate that both equilibrium and kinetic effects may be at play
  5. Biology and physiology can influence water isotope values too.
30
Q

Mixing

A

A process that combines different substrates into the product (the making of a homogenous whole - e.g. baking)

31
Q

Global Meteoric Water Line

A

Plots d2H against d18O
slope =~8
Intercept = +10 per mil

Comprehensive Exams (4 decks)

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