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Warm-Up

Warm-Up. Complete the worksheet you received two classes ago regarding subatomic particles & symbols of atoms. If you have already completed that, work on filling out the front side of the “Atomic Structure Vocabulary & Skills” page you got today. Practice.

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Warm-Up

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  1. Warm-Up Complete the worksheet you received two classes ago regarding subatomic particles & symbols of atoms. If you have already completed that, work on filling out the front side of the “Atomic Structure Vocabulary & Skills” page you got today.

  2. Practice • How many protons, neutrons, and electrons are in the following ions? 7Li +1 40Ca +2 14N -3 112Cd +2 1H +1 1H -1 3 p+, 4 n0, 2 e- 20 p+, 20 n0, 18 e- 7 p+, 7 n0, 10 e- 48 p+, 64 n0, 46 e- 1 p+, 0 n0, 0 e- 1 p+, 0 n0, 2 e-

  3. 1 +1 nucleus 1 0 nucleus outside nucleus negligible (0) -1

  4. 17 Cl 35.453 Looking at the Periodic Table Mass number Cl vs. 35 17 Atomic number symbol Atomic number symbol • What are the similarities? • What are the differences? (Average) Atomic Mass Where does the “35.453” come from?

  5. Isotopes • Atoms with the same number of protons, but different numbers of neutrons. • Atoms with the same atomic number but different mass numbers. • Example: isotopes of chlorine Cl Cl vs. 35 17 37 17 18 neutrons 20 neutrons

  6. More on Isotopes • In nature, elements are found as a mixture of isotopes • Not all isotopes are equally abundant Where does the “35.453” come from?

  7. Isotopes & Atomic Mass • The atomic mass is a weightedaverage of all the atoms of a particular element. Weighted average formula: S(% x mass) Example: • In Ms. Schmoe’s class, tests are worth 50% of the final grade, quizzes are 25%, and homework is 25%. • Joe’s grades in those three areas are 92, 100, and 65, respectively. What is Joe’s final grade?

  8. Joe’s Grade • Since each assignment carries a different weight, we must take this into account in our final grade. (T) 0.50 x 92 = 46.00 (Q) 0.25 x 100 = 25.00 (H) 0.25 x 65 = + 16.25 87.25 How can we apply weighted averages to atomic mass?

  9. Average Atomic Mass Where does the “35.453” come from? • Apply the same steps to calculate the average atomic mass of chlorine. • MASS NUMBER • protons + neutrons • useful in identifying isotopes • refers to one atom • WHOLE NUMBER • ATOMIC MASS • weighted average mass of all the isotopes • found on the PToE • usually a decimal! vs.

  10. - - 0 + + 0 + 0 - ATOM ATOM - - - - 0 0 + + + + 0 0 + + - 0 + + + 0 + - - - Isotope vs. Ion ISOTOPE ION

  11. Learning Check • Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these. • Calculate the average atomic mass of carbon, given the relative abundances below (C-14 abundance is negligible).

  12. Learning Check Answers • 12C: 6p, 6n, 6e • 13C: 6p, 7n, 6e • 14C: 6p, 8n, 6e • Atomic mass (0.989 x 12.0 amu) = 11.868 (0.011 x 13.00335 amu) = + 0.01430 12.011 amu

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