Mole
Atomic mass:
Mole:
Molar Mass:
Avogadro’s number
Vocabulary:
Atomic mass
• the mass of an atom expressed in atomic mass units.
Mole:
• the amount of substance whose number of particles is
the same as the number of atoms in 12 g of carbon-12
Molar Mass:
• the mass in a gram of 1 mole of a substance
Avogadro’s number
• 6.022 x 10^ 23, number of atoms or molecules in a mole.
The Mole
 Number of atoms in exactly 12 grams of
atoms
12C
How many atoms in 1 mole of 12C ?
 Based on experimental evidence
1 mole of 12C = 6.022 × 1023 atoms = 12.011 g
Avogadro’s number = NA
 Number of atoms, molecules or particles in
one mole
 1 mole of X = 6.022 × 1023 units of X
 1 mole Xe = 6.022×1023 Xe atoms
 1 mole NO2 = 6.022×1023 NO2 molecules
Jespersen/Brady/Hyslop
Chemistry: The Molecular Nature of Matter, 6E
3
Finding Molar Mass
Molar mass (also called “molecular weight” or “molecular mass”):
The weight of one mole of a chemical compound. The unit is
“g/mol”.

For elements, the mass of one mole of atoms is called the
“atomic mass” and is found on the periodic table.
How to calculate the molar mass of a compound:
 For elements, the molar mass is the same thing as the atomic
mass.
 For chemical compounds, it’s the sum of the masses of all of
the atoms in the molecule.
Example: NaCl
Na:
Cl:
23 grams x 1 atom =
35 grams x 1 atom =
Total:
23 grams/mol
35 grams/mol
58 grams/mol
 More examples:
o
o
o
MgCl2
Fe(OH)2
Be3(PO4)2
94 g/mol
90 g/mol
217 g/mol
For these last two examples, tell them
that the molar mass for compounds
like this is found by multiplying
everything in the parentheses by the
number outside the parentheses.
Mole calculations:
1 mole of carbon atoms = 6.022x1023 atoms
of carbon = weighs 12 grams
1 mole of oxygen molecules = 6.022x1023
molecules of oxygen = weighs 32 grams
1 mole of NO2 particles= 6.022x1023
particles of NO2 = weighs 30 grams
1
mole
of
fluoride
ion=
23
ions
of

6.022x10
fluoride ions = weighs 19 grams