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Understanding Atomic Mass and Isotopes

Learn about atomic mass, mass number, isotopes, and average atomic mass. Understand the concept of relative atomic mass and how to calculate the average atomic mass of elements using isotope abundances. Discover the significance of isotopes in determining the overall atomic mass.

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Understanding Atomic Mass and Isotopes

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  1. - Atomic Structure II.Masses of Atoms Mass Number Isotopes Relative Atomic Mass Average Atomic Mass

  2. © Addison-Wesley Publishing Company, Inc. A. Mass Number • mass # = protons + neutrons • always a whole number • NOT on the Periodic Table!

  3. Mass # Atomic # B. Isotopes • Atoms of the same element with different mass numbers. • Nuclear symbol: • Hyphen notation: carbon-12

  4. © Addison-Wesley Publishing Company, Inc. B. Isotopes

  5. B. Isotopes • Chlorine-37 • atomic #: • mass #: • # of protons: • # of electrons: • # of neutrons: • 17 • 37 • 17 • 17 • 20

  6. © Addison-Wesley Publishing Company, Inc. C. Relative Atomic Mass • 12C atom = 1.992 × 10-23 g • atomic mass unit (amu) • 1 amu = 1/12 the mass of a 12C atom • 1 p = 1.007276 amu1 n = 1.008665 amu1 e- = 0.0005486 amu

  7. Avg. Atomic Mass D. Average Atomic Mass • weighted average of all isotopes • on the Periodic Table • round to 2 decimal places

  8. Avg. Atomic Mass D. Average Atomic Mass • EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O. 16.00 amu

  9. Avg. Atomic Mass D. Average Atomic Mass • EX: Find chlorine’s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37. 35.40 amu

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