1. III. Masses of Atoms (p.278-281) Atomic Mass Mass Number Isotopes
Ch Atomic Structure
III. Masses of Atoms
(p )
Atomic Mass
Mass Number
Isotopes

2. A. Atomic Mass atomic mass unit (u) 1 u = 1/12 the mass of a 12C atom
1 proton = 1 u 1 neutron = 1 u
1 u = 1.67  g
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3. B. Mass Number
Sum of the protons and neutrons in the nucleus of an atom.
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Always a whole number.
# of neutrons = mass # - atomic #

4. C. Isotopes Mass # Atomic #
Atoms of the same element with different numbers of neutrons.
Isotope symbol:
Mass #
Atomic #
“Carbon-12”

5. C. Isotopes
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6. C. Isotopes Average Atomic Mass reported on Periodic Table
weighted average of all isotopes
Avg.
Atomic
Mass

7. C. Isotopes
EX: About 8 out of 10 chlorine atoms are chlorine-35. Two out of 10 are chlorine-37.
Avg.
Atomic
Mass
35.4 u