The Mole
Common Counting Units
• eggs
dozen (12)
• paper
ream (500 sheets)
• shoes
pair (2)
• pencils
gross (144)
Counting Nails by the Pound
• I want some nails for a project, but
the hardware store sells nails by the
pound!
• How do I know how many nails I
am buying when I buy a pound of
nails?
• Analogy
How many atoms in a certain
mass of an element?
Counting Nails by the Pound
A hardware store customer buys 2.60 pounds of
nails. A dozen of the nails has a mass of 0.150
pounds. How many nails did the customer buy?
Solution map:
Counting Nails by the Pound
1 doz. nails 12 nails
2.60 lbs. 

 208 nails
0.150 lbs.
1 doz.
• The customer bought 2.60 lbs of nails and
received 208 nails. He counted the nails by
weighing them!
Counting Nails by the Pound
• What if he bought a different size nail?
Would a dozen still weight 0.150 lbs?
Would there be 208 nails in 2.60 lbs?
How would this effect the conversion factors?
Chemist’s Counting Units
• need a counting unit for atoms and
molecules
since they are extremely small
• mole = SI unit to measure the amount of a
substance (element or compound)
• 1 mole = the number of atoms in exactly 12
grams of pure carbon-12
mole
• SI base unit to measure the amount of a
substance (element or compound)
Counting Atoms by Moles
• The number of atoms in 12 grams of Carbon-12
is 6.022 x 1023 and we call this a mole
1 mole = 6.022 x 1023 things
Like 1 dozen = 12 things
Chemical Packages - Moles
• mole = number of atoms in 12 g of C-12
1 atom of C-12 weighs exactly 12 amu
1 mole of C-12 weighs exactly 12 g
• The number of atoms in 1 mole is called
Avogadro’s Number = 6.0221421 x 1023
1 mole of C atoms weighs 12.01 g and has
6.022 x 1023 atoms
the average mass of a C atom is 12.01 amu
Avogadro (1776-1856)
Avogadro’s Number
• NA = 6.02 x 1023 of
anything
Avogadro’s Number
• 1 mole = 6.0221367 x 1023 particles
• rounded to 6.02 x 1023 particles
• particles can be
atoms (elements)
molecules
formula units
How Big Is The Mole?
• One mole of marbles would cover the entire Earth to a
depth of fifty miles
• One mole of hockey pucks would equal the mass of
the moon.
• One mole of rice grains is more than the number of
grains of all crops grown since the beginning of time.
• If one mole of pennies was divided up equally between
all the people on Earth, you would have enough money
to spend a million dollars every hour, 24 hours a day,
for your entire life. When you died, you would have
spent less than half of your pennies.
Vocabulary Word
• Avogadro’s number: the number 6.02 x
1023, tells how many pieces (atoms,
molecules or formula units) in a mole
Relationship Between
Moles and Mass
• The mass of one mole of atoms is called the
molar mass
• The molar mass of an element, in grams, is
equal to the element’s average atomic mass
(from the Periodic Table), in amu
Mole and Mass Relationships
Substance Pieces in 1 mole
Weight of 1 mole
hydrogen
6.022 x 1023 atoms
1.008 g
carbon
6.022 x 1023 atoms
12.01 g
oxygen
6.022 x 1023 atoms
16.00 g
sulfur
6.022 x 1023 atoms
32.06 g
calcium
6.022 x 1023 atoms
40.08 g
chlorine
6.022 x 1023 atoms
35.45 g
copper
6.022 x 1023 atoms
63.55 g
1 mole
Sulfur
32.06 g
1 mole
Carbon
12.01 g
Molar Mass
• the mass (in grams) of a mole of substance
• On your periodic tables
• Round to the nearest tenth
 Hydrogen is 1.00797  1.0 g/mol
Molar Mass is an INTENSIVE property—
doesn’t depend on amount
Vocabulary Word
• molar mass: mass in grams of a mole any
pure substance
Moles of Compounds Too
Molecular Weight of Compounds
• the molecular weight of molecules can be
calculated by adding up the atomic masses
Formula Mass = 1 molecule of H2O
= 2(1.01 amu H) + 16.00 amu O = 18.02 amu
• since 1 mole of H2O contains 2 moles of H and 1
mole of O
Molar Mass = 1 mole H2O
= 2(1.01 g H) + 16.00 g O = 18.02 g
Mole Relationships in
Chemical Formulas
• since we count atoms and molecules in mole
units, we can find the number of moles of an
element in a compound
Moles of Compound
1 mol NaCl
1 mol H2O
1 mol CaCO3
Moles of Constituents
1 mole Na, 1 mole Cl
2 mol H, 1 mole O
1 mol Ca, 1 mol C, 3 mol O
1 mol C6H12O6
6 mol C, 12 mol H, 6 mol O
Converting from moles to
particles
• use conversion factors
• how many roses are in 3.5 dozen?
3.5 dozen  12 roses = 42 roses
dozen
mole conversions
• how many particles are in 3.50 moles of
sucrose?
3.50 moles  6.02 x 1023 particles
mole
21.1 x 1023  2.11 x 1024 particles
particle to mole conversions
• how many moles are in 4.50 x 1024 atoms of
Zn?
4.50 x 1024 atoms 
1 mole
6.02 x 1023 atoms
7.48 moles Zn