Presentation on theme: "Analyze Stable Isotopes Climatologists have many strategies for developing an understanding of patterns of climate change."— Presentation transcript:
Analyze Stable Isotopes Climatologists have many strategies for developing an understanding of patterns of climate change.
Many students are familiar with the use of unstable isotopes to go back in time. http://www.physlink.com/Education/askExperts/ae403.cfm
This worksheet activity guides students toward a very basic understanding of how a study of stable isotopes found in the ice of the Polar Regions can be used to study Earths climate history.
Students begin by indicating the number of protons and neutrons in nuclei of a stable isotopes. Isotope# of Protons # of Neutrons Atomic Mass Natural Abundance 1H1 1H1 101.007899.9885% 1H2 1H2 112.01410.0115%
Students then compare the masses of two stable isotopes of an element. For example: Question 4: How much more massive is a H-2 isotope than a H-1 isotope? a. Express the different in atomic mass units. 2.0141 amu 1.0078 amu = 1.0063 amu b. Express the difference as a percentage and express the percent difference in words. (1.0063 amu ÷ 1.0078 amu) x 100 = 99.85% This means that H-2 isotopes are 99.85% more massive than H-1 isotopes.
Students calculate the average mass of the stable isotopes of an element. Question 5: What is the average atomic mass of hydrogen atoms in a sample of stable isotopes of hydrogen? (1.0078 amu x 0.999885) = 1.0076841 amu + (2.0141 amu x 0.000115) = 0.0002316 amu 1.0079157 amu
Students compare the average atomic mass they have calculated with a value on a Periodic Table of the Elements Question 6: How does your answer to Question 5 compare with the average atomic mass of hydrogen on a Periodic Table of the Elements? Many Periodic Tables of Elements indicate that the atomic mass of Hydrogen is 1.00794 amu. The average mass of stable isotopes was slightly smaller. Hydrogen-3 is an unstable isotope with a half life of 4500 days. Its presence in a hydrogen sample will increase the average atomic mass of hydrogen atoms.
Students are posed questions about the precipitation of water vapor as it is transported toward the Polar regions. Question 7: What combination of stable isotopes in water molecules could result in water vapor having a greater tendency to form precipitation as it is transported toward a Polar Regions? Provide a rationale for your answer. A combination of Hydrogen-2 and Oxygen-18 atoms would result in a water molecule that would be much more likely to form precipitation. As the temperature of water vapor decreases, more massive water molecules would decrease their speed more rapidly and form cloud droplets on condensation nuclei.
The web site below can be used to help students visualize the relationships among the temperature, kinetic energy, and velocity of particles. It can also be used to illustrate the relationships among temperature, kinetic energy, mass, and velocity of particles. http://www.classzone.com/books/ml_science_share/vis_sim/mem05_pg101 _kintheory/mem05_pg101_kintheory.html
Solving the kinetic energy equation for velocity also reveals the affect of mass on the velocity of objects.
Students are asked to explain how water molecules in different layers of ice in the Polar Regions may have different isotopic ratios Question 10: Why would fewer water molecules containing the more massive isotopes reach the Polar Regions during winter months or during an Ice Age? Water molecules containing one ore more massive isotope of hydrogen and/or oxygen would have had a greater probability of forming precipitation at lower Latitudes as the water vapor is transported toward the Polar Regions.
Drilling deep into an ice sheet http://researchnews.osu.edu/archive/lonthmppics.htm
Removing an ice core http://researchnews.osu.edu/archive/lonthmppics.htm
Suppose a student asks: How are the distribution of isotopes in a molecule determined? You might ask the student: How would the mass of an isotope affect its ability to change direction?
A mass spectrometer ionizes isotopes in molecules. Ions of different masses are deflected by different amounts by a magnet. http://en.wikipedia.org/wiki/Isotope_ratio_mass_spectrometry
This worksheet activity provides opportunities for students to: Refresh their knowledge of or be introduced to the structure of isotopes. Develop a better understanding of the average atomic mass of an element. Apply their understanding of or be introduced to relationships among kinetic energy, temperature, mass, and velocity. Recognize one of many ways that the composition of ice in the Polar Regions changes as Earths climate changes.
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