RR: How many ways can you
count to 100?
Do you know how to count?
• In chemistry, the unit that helps us count is the mole (mol).
• The mole represents 6.022 x 1023 pieces of something.
6.022 x 1023 = 602,200,000,000,000,000,000,000
called Avogadro’s number
In chemistry, our pieces are atoms, particles, ions,
molecules, etc.
• We can express the mole mathematically as a conversion
factor – a mathematical ratio used to express a relationship
between different units.
Avogadro’s Number and the Mole
• The relationship between Avogadro’s number and the mole
written as a conversion factor:
6.022 𝑥 1023
1 𝑚𝑜𝑙
𝑂𝑅
1 𝑚𝑜𝑙
6.022 𝑥 1023
There are 6.022 x 1023 pieces per mole.
RR: How many atoms are in 1.0 mole of
carbon?
Known
Unknown Relationship
(what you have) (what you need) (conversion factor)
Shown Work
Answer
RR: How many molecules of KBr are in 5
moles of KBr?
Known
Unknown Relationship
(what you have) (what you need) (conversion factor)
Shown Work
Answer
RR: What units do we use to measure mass in
chemistry?
Mass and the Mole
• Elements on the periodic table are measured in atomic mass
units, but most of the time, chemists use grams instead.
• Each element’s mass is located on the periodic table.
• We can find the molar mass (mass per mole) of each
element by dividing the mass of the element by the moles
of the element.
• For a single mole of an element, the mass is the same as
the mass on the periodic table.
• Example: What is Carbon’s molar mass?
Molar Mass of a Molecule or Compound
• If we know the number of moles of each element, we
can find the total mass of a molecule by adding
together the molar masses of each element.
• Note, moles ≠ atoms
How can we determine the mass of 1 mole of
glucose, C6H12O6?
• First, break the molecule into pieces.
• Next, determine the mass for each piece (element) by
using the molar mass.
• Total the masses of the different pieces.