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Mass of Individual Atoms

Mass of Individual Atoms. Review: Mass of proton = 1.673 x 10 -24 g Mass of neutron = ? Mass of electron = 9.11 x 10 -28 g An atom of K-39, has ____ protons, _____ neutrons, and ______ electrons. Who wants to add up that actual mass?!?!. Mass of Individual Atoms (cont.).

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Mass of Individual Atoms

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  1. Mass of Individual Atoms • Review: • Mass of proton = 1.673 x 10-24 g • Mass of neutron = ? • Mass of electron = 9.11 x 10-28 g • An atom of K-39, has ____ protons, _____ neutrons, and ______ electrons. • Who wants to add up that actual mass?!?!

  2. Mass of Individual Atoms (cont.) • We ALL want to work with whole numbers, so scientists came up with the atomic mass unit (amu). • Def.: 1/12 the mass of a carbon-12 atom (ALMOST equal to the mass of 1 proton or 1 neutron)

  3. Mass of Individual Atoms (cont.) • Review: What does the mass number of an element tell you? • The mass recorded on the periodic table for an element is called atomic mass. • Atomic mass is determined by the weighted average mass of the isotopes of that element.

  4. Mass of Individual Atoms (cont.) • What is the atomic mass for chlorine? • Chlorine exists naturally as a mixture of 75.770% Cl-35 and 24.230% Cl-37. • What does Cl-35 and Cl-37 mean? • The ACTUAL masses of these isotopes would be 34.969 amu and 36.966 amu. • The math: (75.770% x 34.969) + (24.230% x 36.966) = 35.453 amu • What was the atomic mass of chlorine? 

  5. Practice & Assignment • To calculate atomic mass: • Calculate mass contribution of each isotope by multiplying its mass x its % abundance • Add together all the mass contributions. • P.104: 15-16 • Study Guide Workbook: pp. 22-23 (24-33)

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