Transcript Atomic Mass

Chapter 6
Chemical Quantities
6.1
Atomic Mass and Formula Mass
Copyright © 2008 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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Atomic Mass
Atomic mass is the
• Mass of a single atom in
atomic mass units (amu).
• Mass of an atom
compared to a 12C atom.
• Number below the
symbol of an element.
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Periodic Table and Atomic Mass
Ag has
atomic
mass =
107.9 amu
S has
atomic mass
= 32.07 amu
C has atomic mass
= 12.01 amu
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Atomic Mass Factors
The atomic mass
• Can be written as an equality.
Example: 1 P atom = 30.97 amu
• Can be written as two conversion factors.
Example: 1 P atom and 30.97 amu
30.97 amu
1 P atom
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Uses of Atomic Mass Factors
The atomic mass factors are used to convert
• A specific number of atoms to mass (amu).
• An amount in amu to number of atoms.
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Using Atomic Mass Factors
1. What is the mass in amu of 75 P atoms?
75 P atoms x 30.97 amu = 2323 amu (2.323 x103 amu)
1 P atom
2. How many Cu atoms have a mass of 4.500 x 105
amu?
4.500 x 105 amu x
6
1 Cu atom = 7081 Cu atoms
63.55 amu
Learning Check
What is the mass in amu of
75 silver atoms?
1) 107.9 amu
2) 8093 amu
3) 1.439 amu
Copyright © 2008 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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Solution
What is the mass in amu of 75 silver atoms?
2) 8093 amu
75 Ag atoms x 107.9 amu = 8093 amu
1 Ag atom
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Learning Check
How many gold atoms have
a mass of 1.85 x 105 amu?
1) 939 Au atoms
2) 3.64 x 107 Au atoms
3) 106 Au atoms
Copyright © 2008 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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Solution
How many gold atoms have a mass of
1.85 x 105 amu?
1) 939 Au atoms
1.85 x 105 amu x 1 Au atom = 939 Au atoms
197.0 amu
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Formula Mass
The formula mass is
• The mass in amu of a compound.
• The sum of the atomic masses of the elements
in a formula.
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Copyright © 2008 by Pearson Education, Inc.
Publishing as Benjamin Cummings
Calculating Formula Mass
To calculate the formula mass of Na2SO4
• Multiply the atomic mass of each element by its
subscript, then total the masses of the atoms.
2 Na x 22.99 amu = 45.98 amu
1 Na
1 S x 32.07 amu = 32.07 amu
1S
4 O x 16.00 amu = 64.00 amu
1O
12
142.05 amu
Learning Check
Using the periodic table, calculate the formula
mass of aluminum sulfide Al2S3.
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Solution
Using the periodic table, calculate the formula
mass of aluminum sulfide Al2S3.
2 Al x 26.98 amu = 53.96 amu
1 Al
3 S x 32.07 amu = 96.21 amu
1S
150.17 amu
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