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ISOTOPES

ISOTOPES. Other than Homer's baseball team, what are Isotopes???.

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ISOTOPES

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  1. ISOTOPES

  2. Other than Homer's baseball team, what are Isotopes??? • Isotopes are atoms of the same element with different numbers of neutrons. This one fact gives each isotope of a particular element a different mass, BUT, being the same element they have the same atomic, or proton, number and are identical chemically.

  3. So how are they different from one another? • There are small physical differences between isotopes of an element. For example, the heavier isotope has a greater density or boiling point.

  4. Because isotopes have the same number of protons (recall-proton # = atomic #) isotopes of a particular element have the same electronic structure. • For example: • C14 and C12 both have atomic # 6 and each has the same electron arrangement. However, C-12 has 6 neutrons in its nucleus while C-14 has 8 neutrons in its nucleus.

  5. The same can be shown for Na24 and Na23 (Na24 has 13 no andNa 23 has 12 no) , He4 and He3 or any of the many different isotopes.

  6. ISOTOPES AND RADIOACTIVITY • DO NOT assume the word isotope meansthat the atom is radioactive. Radioactivity depends on the stability of the nucleus. • In unstable atoms (radioactive atoms) AKA radio-isotopes the nucleus is unstable and will throw off neutrons. Most isotopes are stable, NOT radioactive, and are present in most, if not all, of the atoms that make up the world around us.

  7. HOW ISOTOPES AFFECT AN ATOM'S MASS • You will note on your periodic tables that the atomic mass of an atom is never a whole number. This is because the atomic mass is calculated using a weighted average of the different isotopes.

  8. ISOTOPE ABUNDANCE • each isotope is present as a fraction of the total mass of a sample • this fraction is the isotopic abundance , often expressed as a percent (%) • the average atomic mass is the weighted average of each isotope present on earth, • the isotopic abundance of each element is fixed—it is the number we see on the periodic table

  9. So, how can we calculate the atomic mass of an atom ? • Here is the data. Find the average atomic mass of potassium. Compare your answer to the one on your periodic table • K-39 – 93.26%, K-40 – 0.01% and K-41 – 6.73% • Try another: Determine the average atomic mass of Rubidium. Compare your answer. • Rb-85 – 72.17% and Rb-87 – 27.83%

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