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Atomic Mass Calculation and Isotope Abundance Equations

Understand isotopic calculations, atomic masses, and periodic table concepts. Learn to calculate isotope masses, abundance percentages, and average atomic masses. Practice solving problems using isotopic data and formulas.

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Atomic Mass Calculation and Isotope Abundance Equations

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  1. First SAT given (1926) • Reading: Chapter 5 sections 1-5 (quiz) • Electron Configuration HW Due Tomorrow • HW 11: DUE Tomorrow • Chap. 11#’s 36, 45, 47, 49-52 (all), 59, 60, 63, 64, 65, 67, 99 (no extra credit) • HW #5.1: DUE Wednesday • 3, 4, 5, 8, 9, 11, 13, 25-35 (odd), 41, 45, 49, 57, 80, 81, 85, 89 • HW #5.2: DUE Thursday • 17, 19, 21, 39, 43, 47, 53, 59, 71-77 (all), 83 • For lab tomorrow (dry lab)

  2. Atomic Masses • Measured in the unit amu • Stands for atomic mass unit • Defined as 1/12th the mass of a 12C atom • 35Cl = 34.9689 amu • 50V = 49.9472 amu • 79Br = 78.9183 amu • Are these what the P.T. say?

  3. All Isotopes are NOT Created Equal • Weighted averages • An equation (oh crap) • 35Cl = 34.9689 amu • Abundance = 75.77% • 37Cl = 36.9659 amu • Abundance = 24.23% • These must be the only 2 isotopes... Why?

  4. All Isotopes are NOT Created Equal • 35Cl = 34.9689 amu • Abundance = 75.77% • 37Cl = 36.9659 amu • Abundance = 24.23% =0.7577 =0.2423

  5. All Isotopes are NOT Created Equal • 35Cl = 34.9689 amu • Abundance = 75.77% • 37Cl = 36.9659 amu • Abundance = 24.23% =0.7577 Where have I seen this before? =0.2423 x 0.2423 = 35.45amu x 0.7577 34.9689 + 36.9659 Periodic Table gives AVERAGE ATOMIC MASS in amu!!

  6. Some Algebra and a New Equation decimal, not % (i.e. 0.1234 not 12.34%) For solving for % abundance multiply by 100 to get percentages

  7. Isotopes Calculation Summary • DO NOT use “normal” averages • If asked for two percent-abundances, use: • If asked for ANYTHING else:

  8. A Problem! What is the average atomic mass of magnesium? 78.90% of all magnesium is 24Mg  23.985 amu 10.00% of all magnesium is 25Mg  24.986 amu 11.10% of all magnesium is 26Mg  25.983 amu 11.10% 100.00% = 24.30 amu

  9. Another Problem! Lead has 4 isotopes, the masses and abundances of which can be found in the following table. Your job? Calculate the isotope mass of lead-207. 22.10% ???? X = Lead-207 = 206.9 amu

  10. A Problem! Bromine has 2 isotopes, and . has a mass of 78.9193 amu and has a mass of 80.9163 amu. What are the percent abundances of each of the isotopes?  Abundance 1 = 50.44%  Abundance 2 = 49.56%

  11. A Problem! Thallium has 2 isotopes, and . has a mass of 202.973 amu and has a mass of 204.974 amu. What are the percent abundances of each of the isotopes?  Abundance 1 = 30.2%  Abundance 2 = 69.8%

  12. The Modern Periodic Table • Mendeleev • Set up the periodic table based on atomic mass • Moseley • Set it up by atomic number rather than atomic mass • Periodic Law – properties occur in a repeating pattern when set up by atomic number.

  13. The Modern Periodic Table • Periods (series) • Labeled 1 - 7

  14. The Modern Periodic Table • Groups (families) • Columns • 2 different labeling systems • 1-18 • A-B

  15. A few definitions… • Main Group Elements: • Groups 1 and 2 and 13 – 18 • Groups A

  16. Main Group Elements

  17. A few definitions… • Main Group Elements: • Groups 1 and 2 and 13 – 18 • Groups A • Transition Elements: • Groups 3 – 12 • Groups B

  18. Transition Elements

  19. Groups of Elements • Vertical columns are called groups • Group 1 = Alkali Metals

  20. Alkali Metals

  21. Groups of Elements • Vertical columns are called groups • Group 1 = Alkali Metals • Group 2 = Alkaline Earth Metals

  22. Alkaline Earth Metals

  23. Groups of Elements • Vertical columns are called groups • Group 1 = Alkali Metals • Group 2 = Alkaline Earth Metals • Group 17 = Halogens

  24. Halogens

  25. Groups of Elements • Vertical columns are called groups • Group 1 = Alkali Metals • Group 2 = Alkaline Earth Metals • Group 17 = Halogens • Group 18 = Noble Gases

  26. Noble Gases

  27. The Modern Periodic Table • Representative elements • Also known as main group elements • Transition metals • Inner transition metals • Lanthanide series

  28. Lanthanide Series

  29. The Modern Periodic Table • Representative elements • Also known as main group elements • Transition metals • Inner transition metals • Lanthanide series • Actinide series

  30. Actinide Series

  31. Diatomic Elements • Elements that exist as diatomic molecules when UNCOMBINED (meaning not in a compound with other elements). H2, N2, O2, F2, Cl2, Br2, I2

  32. Diatomic Elements • Elements the exist as diatomic molecules when UNCOMBINED (meaning not in a compound with other elements). H2, N2, O2, F2, Cl2, Br2, I2 NaCl BiF5 K3N Examples of when these elements are NOT diatomic AlI3 TiBr4

  33. IONS!!

  34. Atoms vs. Ions • Atoms are NEUTRAL!!!!! • This means that they have zero charge • #p+ = #e-

  35. Charge!!! e- = -1 p+ = 1 + 0 47 e- = -47 47 p+ = 47 + 0 When #p+ = #e-, the atom has no charge and is neutral

  36. Atoms vs. Ions • Atoms can gain or lose e- to form IONS • ANY charged particle is called an ion • Losing e- gives POSITIVELY charge

  37. Charge!!! When an atom LOSES electrons 11 p+ = 11 -10 10 e- = 11 e- = +1

  38. Atoms vs. Ions • Atoms can gain or lose e- to form IONS • ANY charged particle is called an ion • Losing e- gives POSITIVELY charge • Called cations • Usually formed from metals • Gaining e- gives a NEGATIVELY charged ion

  39. Atoms vs. Ions • Atoms can gain or lose e- to form IONS • ANY charged particle is called an ion • Losing e- gives POSITIVELY charge • Called cations • Usually formed from metals • Gaining e- gives a NEGATIVELY charged ion • Called anions • Usually formed from non-metals

  40. Charge!!! When an atom LOSES electrons 11 p+ = 11 10 e- = -10 +1 16 p+ = 16 When an atom GAINS electrons -18 16 e- = 18 e- = -2

  41. Atoms vs. Ions • Atoms can gain or lose e- to form IONS • ANY charged particle is called an ion • Losing e- gives POSITIVELY charge • Called cations • Usually formed from metals • Gaining e- gives a NEGATIVELY charged ion • Called anions • Usually formed from non-metals

  42. How many electrons are needed to be neutral? 15 protons

  43. 15 protons 2 electrons

  44. 15 protons 10 electrons

  45. Total charge = 0 Stable!!! 15 protons 15 electrons

  46. Valence electrons are the outermost electrons

  47. Total charge = p+ - e- = 15 – 18 = -3 Stable!! 15 protons 18 electrons

  48. How many electrons are needed to be neutral? 12 protons

  49. 12 protons 2 electrons

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