Atomic Masses
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Transcript Atomic Masses
Chemical Composition
Chapter 6
Counting by Massing
If we know the mass of one object, we can
figure out how many there are by taking the
total mass.
Example: If each barrel holds 55 gal of oil, how
many barrels were used to fill a 22,550 gal tank?
22,550 gal
410 barrels
Apples have an average mass of 350. g each. How
many apples are in a 16.5 kg crate?
16.5 kg 1000 g 1 apple 47.1 apples
1 kg
350. g
OR 47 apples
Atomic Masses
Atomic mass is described in terms of
Atomic Mass Units (AMU)
1 AMU = 1.66 x 10-24 g
OR 0.00000000000000000000000166 g
Atomic Masses on Periodic Tables are an average
of all of the isotopes
Average Lithium (Li) atom 6.94 AMU
Average Tungsten (W) atom 183.94 AMU
Examples
What is the mass of 2,100 atoms of Al?
2100 atoms 26.98 AMU 57,000 AMU
1 atom Al
How many atoms of Nickel would it take to have
a mass of 19,190 AMU?
1 atom Ni
19,190 AMU
326.9 atoms of Ni
58.71 AMU