Isotopes and standards Flashcards
What is an isotope?
atoms with an equal number of protons and electrons but different number of neutrons – making them either heavy or light
What is the proportion of different carbon isotopes?
C12= 98.9%
C13= 1.1%
C14= <0.0001%
What is the ratio of C13/C12?
0.011
What is the stability of carbon isotopes like?
C12 and C13- stable
C14- radioactive and unstable
Why are isotopes imporant?
Carbon dating
Trace food sources through a food web
Tracking pollution through an environment
What is used to measure isotopes?
elemental analyser-
What is it difficult to do with isotopes?
measure absolute amounts of stable isotopes so a standard will be used
What are some examples of standards?
Vienna Standard Mean Ocean Water
Pee Dee Belemnite
Canyon Diablo Troillite
How does using standards help measure isotopes?
If there are more “heavy” carbons,
the δ value will be more positive i.e.
“Heavier”
or
fewer heavy carbon will be lighter
What does fractionation do?
changes relative proportions of heavy and light isotopes.
Usually prefers lighter isotope in reactions
What are the 2 types of fracitonation?
Kinetic
Equilibrium
What is kinetic fractionation?
heavier isotope less mobile
What is equilibrium fractionation?
heavier isotope has higher binding energy
How can oxygen istopes be an example of fractionation?
Less energy needed to evaporate O16 so they enter atmo more readily when reach land and precipitate heavier O18 fall more readily