Moles, Molecules and Atoms
How you measure how much?
 You can measure mass,
 or volume,
 or you can count pieces.
 We measure mass in grams.
 We measure volume in liters.
 We count pieces in MOLES.
The Mole
 Defined as the number
of carbon atoms in
exactly 12 grams of
carbon-12.
 1 mol is 6.02 x 1023
representative particles
 Treat it like a very large
dozen
 6.02 x 1023 is called
Avogadro’s number.
Representative Particles
 The smallest pieces of a substance.
 For a molecular compound, it is a
molecule.
 For an ionic compound, it is a formula
unit. (or individual ions)
 For an element, it is an atom.
Determining the Molar Mass
 The mass of one mole
 Examples:
of a substance in
grams.
 For an Element:
 Gram Atomic Mass
(GAM)
 Use average atomic
mass or atomic
weight from periodic
table.
Calcium
Iron
For a Compound
 In 1 mol of H2O molecules, there are two
moles of H atoms and 1 mole of O atoms
 To find the mass of one mole of a compound
 determine the moles of the elements
contained in compound
 Find out their molar mass
 Add them up
For a compound cont’
 For an ionic
compound:
 Gram Formula Mass
 GFM
 For a molecular
compound:
 Gram Molecular
Mass
 GMM
Example: Calculate the
gram formula mass of gold
(III) oxide. Au2O3
More Examples:
 Calculate the molar mass of the following:
1.
Na2SO4
2. Al(NO3)3
3. CO2
Review Problems
1.
Ca(NO3)2
2. C6H12O6
3. (NH4)3PO4
Dimensional Analysis using moles, grams and
Avogadro’s Number
Dimensional Analysis Review:
1.
A student lives 3,500 ft from the high school.
Determine the distance in miles.
2. A child drinks 2.0 liters of Mountain Dew for breakfast
before school. How many gallons of soda did he
consume?
Finding the Conversion Factor
1 mol = molar mass (g) = 6.02 X 1023 particles
Ex. What is the molar mass of ethanol
(C2H5OH)?
Therefore 1 mol of ethanol has a mass of
46.069-g and contains 6.02 X 1023 molecules of
ethanol.
Types of Problems:
1. If a scientist needs 2.75 mol of ethanol to complete
an experiment, how many grams of the substance
does she need?
2. If the density of ethanol is 0.791 g/mL, how many
milliliters would she measure out?
Types of Problems:
3. Calculate the number of molecules of water
contained in a 12.3-g sample of the liquid.
4. A sample of carbon contains 9.67 X 1024 atoms.
What is the mass of the sample?
Types of Problems:
5. A sample of carbon tetrachloride contains 4.51 X 1022
molecules. What is the mass of the sample of carbon
tetrachloride?
Types of Problems:
6. Isopentyl acetate (C7H14O2) is the compound responsible
for the scent of bananas. Bees release about 1.00 X 10-6
grams of this compound when they sting. The resulting
scent attracts other bees to join the attack. How many
molecules of isopentyl acetate are released in a bee sting?
Molar Volume of a Gas
 At STP, 1 mol or 6.02 X 1023 molecules of
any gas occupies a volume of 22.4-L.
 STP = Standard Temperature and Pressure
 The converting factor:
 1 mol = 22.4 L of a gas
Examples:
1. Sulfur dioxide is a gas produced by burning coal.
Determine the volume, in liters, of 0.60 mol of SO2
at STP.
2. At STP, calculate the number of moles of carbon
dioxide gas in a 14.2-L sample of the gas.