Isotopes

Question 1

Light isotopes

Answer 1

Isotopes of elements with atomic number below 8

Question 2

Heavy Isotopes

Answer 2

isotopes of elements with atomic number typically above 70

Question 3

Stable Isotopes

Answer 3

the number of protons and neutrons in these nuclei will not be modified under any naturally occurring circumstances and processes on earth: their nucleus will remain strictly as it is

Question 4

Radioactive Isotopes

Answer 4

have unstable nuclei and disintegrate at a constant rate by emitting particles and energy

Question 5

Radiogenic Isotopes

Answer 5

produced by the disintegration of radioactive isotope

Question 6

Cosmogenic isotopes

Answer 6

produced by cosmic radiation in the upper reaches of the atm

Question 7

Kinetic fractionation

Answer 7

dominant fractionation when rapid and nonreversible reacitions occur (evaporation, diffusion)

Caused by difference in diffusion rates between isotopes of the same elements—> due to differences in activation energy between two isotopes of different mass

Lighter elements diffuse faster than heavier ones (products therefore always lighter than reactants

Question 8

Fractionation

Answer 8

Isotopes of same element will have the same chemical characteristics; however difference in mass will result in slight difference in behaviour, causing different isotopes of the same element to partition between different compounds or phases: fractionation

Question 9

Equilibrium fractionation

Answer 9

occurs when reversible reactions occur (equilibrium)

Lower extent of fractionation, caused by the difference in bonding energy between isotopes,

Difference in density caused by different mass and therefore bonding energy

Higher mass on isotope = higher dissociation energy (bonding energy)

Question 10

How is α defined and why is it important?

Answer 10

It is the fractionation factor, defined as the ratio between the isotope ratios in two compounds at equilibrium
quantifies the extent of fractionation

Question 11

How doe temp affect the fractionation factor

Answer 11

The higher the temperature, the lower the extent of fractionation

Question 12

What is the “Global Meteoric Water Line” and what is its importance? What are the secondary factors affecting the “Global Meteoritc Water Line”?

Answer 12

d18O versus d2H
- shows how water becomes lighter with each subsequent precipitation

affected by:
- altitude: more depleted heavy isotope with height
- Latitude: depleted more south/north of equator
- Distance from coast: more depleted further from coast
- Amount effect: more precipitation, more depletion of heavy isotope

Question 13

Rayleigh fractionation

Answer 13

Rayleigh distillation is a process of isotopic fractionation in an open system, where one phase is removed from the system and is no longer in contact and isotopic equilibrium with the other phase
Allows us to quantify the isotopic composition of the two phases at any point of the evaporation processs

Question 14

How does humidity affect the fractionation of water during evaporation?

Answer 14

more humid environments will produce fractionations closer to that produced at equilibrium as there is more humidity in the air with which the evaporated water can stay in