Isotope Class Notes

Subatomic Particles Label the atom:

What are Isotopes? First, do you remember how to find the number of neutrons in an atom? Write the equation down in your notes

What are Isotopes Isotopes are atoms that have a different number of neutrons. An atom is still the same element if it is missing a neutron- it’s just a different version! Neutrons can be added to an atom without altering the number of protons and electrons it has.

Carbon Isotopes For example, the element carbon has 13 different isotopes! You are familiar with C-12 (the C stands for carbon, and the 12 is it’s atomic mass) –This isotope has 6 neutrons C-14 (atomic mass 14) is used for carbon dating and has 8 neutrons!

More about Isotopes In an isotope, the number of protons and electrons never changes- only the number of neutrons is different This means that each isotope of a particular element has a different atomic mass than another isotope of the same element –Remember: C-12 has an atomic mass of 12 and C-14 has an atomic mass of 14!

Count the Number of Protons and Neutrons

Applications of Isotopes Carbon dating Carbon-14 is created by the bombardment of the atmosphere by cosmic rays.It is an unstable radioactive isotope of C=12. After creation it finds its way into living organisms. When an organism dies no more C-14 is added and what C-14 is present continues to decay. To date artifacts scientists compare the number of C-14 atoms to the more common C-12 atoms in the artifact. This ratio along with the half-life of radioactive C-14 allows dating to occur.

Applications of Isotopes Structural determination of compounds –Isotopes are used to trace the formation of structures by acting as labels. Medical Uses –Isotopes are used for diagnosis in medicine. –Sodium-24 used to trace blood flow in the body so that obstructions can be detected. –Iodine-131 has been used to test the activity of the thyroid gland

Chemistry in the Environment The processing of uranium ore for nuclear fuel produces large amounts of radioactive mill tailings. Until the late 1970’s disposal of the radioactive tailings was not controlled. As a result, millions of tons of these radioactive tailings are present in unmarked sites across the United States and Canada.

Quick Activity Calculate the number of neutrons there are in the following isotopes (use your periodic table to find the atomic numbers) 1)Carbon-14 2)Nitrogen-15 3)Sulfur-35 4)Calcium-45 5)Iodine-131

Calculating Atomic Mass Based on Isotopes Most elements exist as several different isotopes. For example, chlorine has two naturally occurring isotopes: chlorine-35 chlorine % of the chlorine in the world exists as chlorine-35, and 24.23% exists as chlorine-37.

Calculating Atomic Mass Based on Isotopes This is why the atomic masses on the periodic table are not WHOLE numbers. If we know how much of each isotope exists in the world, we can calculate the average atomic mass of that element (which is the number you find on the periodic table).

Example: Chlorine exists as two different isotopes, chlorine-35 and chlorine-37. Given that 75.77% of chlorine is chlorine-35 and the other 24.23% is chlorine-37, calculate the average atomic mass of chlorine. Verify your answer using the periodic table.