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More about isotopes

More about isotopes. Atomic mass vs average atomic mass or atomic weight. Atomic Mass. The mass of a specific isotope of an element expressed in atomic mass units (amu) The atomic mass is the total mass of the protons, neutrons and electrons in the atom Atomic mass = mass of an atom

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More about isotopes

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  1. More about isotopes Atomic mass vs average atomic mass or atomic weight

  2. Atomic Mass • The mass of a specific isotope of an element expressed in atomic mass units (amu) • The atomic mass is the total mass of the protons, neutrons and electrons in the atom • Atomic mass = mass of an atom • This is what we refer to in our isotope expression, eg.

  3. Average Atomic Mass (also called Atomic Weight) Atomic Number Symbol of element Atomic Weight 1 H 1.008 This is the number that you see in the periodic table. This is the weighted average of the all of the isotopes of Hydrogen

  4. What is a Weighted Average? • The isotopes of an element do not occur with equal frequency or amounts • For example, the relative abundances for the three carbon isotopes are: • carbon-12 98.9% • carbon-13 1.1%, • carbon-14 <001%. • The "average" mass for the atoms of an element is dictated by the most abundant or common isotope • The atomic weights in the periodic table = weighted averages • Tabulated atomic weight value doesn't match any actual atom, but is closer to the weight for the most common isotope • We’ll follow the steps of how to calculate a weighted average next….

  5. Calculating Weighted Average weighted average = ( decimal fraction A) mass A + ( decimal fraction B) mass B • Carbon-12 atomic mass = 12 amu; abundance = 98.9% • Carbon-13 atomic mass = 13 amu; abundance = 1.1% • Carbon-14 atomic mass = 14 amu; abundance = 0.001% Atomic weight = (0.989 * 12) + (0.011 * 13) + (0.00001 * 14) = 12.011 6 C 12.011

  6. Average Atomic Mass Worksheet Homework - I will post answers on website Monday. You will have to show ALL of your work.

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