Welcome to the Periodic Table

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THE MOLEUnit 7
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How Scientists Keep Track of Atoms

• One way to measure how much substance available
  is to count the of particles in that sample
• However, atoms molecules are extremely small
• Also, the of individual particles in even a
  small sample is very large
• Therefore, counting the of particles is not a
  practical measure of amount
• To solve this problem, scientists developed the
  concept of the mole
• Its the chemical counting unit

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• Just as a dozen eggs equals 12 eggs, a mole
  602,000,000,000,000,000,000,000
• It is equal to that number no matter what kind of
  particles youre talking about
• It could be represent marbles, pencils, or bikes
• usually deals with atoms and molecules
• The word mole was introduced about 1896 by
  Wilhelm Oswald, who derived the term from the
  latin word moles meaning a heap or pile.
• The mole, whose abbreviation is mol, is the SI
  base unit for measuring amount of a pure
  substance.

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• The mole, as a unit, is only used to count very
  small items
• Represents a of items, so, we can know exactly
  how many items are in 1 mole
• The experimentally determined number a mole is
  called, Avogadros Number.
• Or 6.02x1023
• The term representative particle refers to the
  species present in a substance
• Usually atoms
• Molecules
• Or formula units (ions)

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CHEMICAL
REP. PARTICLE
REPRESENTATIVE
SUBTANCE
FORMULA
PARTICLE
IN 1 MOL
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How Do We Use The Mole?

• Wed never use the mole to describe macroscopic
  or real world objects.
• 1 mole (6.02x1023) of watermelon seeds would be
  found inside a watermelon the size of the moon.
• 1 mole (6.02x1023) of donut holes would cover the
  earth and would be 5 miles deep.
• Since the mole is such a huge number of items, it
  is only used to describe the amount of things
  that are very, very small.
• 1 mole (6.02x1023) of water molecules would
  barely fill a shot glass

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Using the mole in calculations 1

• What number of moles of Mg is equivalent to
  1.806x1024 atoms of Mg?

Remember 1 mol Mg 6.02x1023 atoms Mg
1 mole Mg
X mole Mg
6.02x1023 atoms Mg
1.806x1024 atoms Mg
(6.02x1023 atoms Mg)(X mole Mg)
(1.806x1024 atoms Mg)(1 mole Mg)
(6.02x1023atmMg)(X)(1.806x1024atmsmolsMg)
X 3.0 moles
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Using the mole in calculations 2

• If we had 2.5 moles of sugar, how many molecules
  of sugar is that equal to?

Remember 1 mol sugar 6.02x1023 molecules sugar
1 mole sugar
2.5 moles sugar
6.02x1023molec sugar
X molec sugar
(1mole sugar)(X molec sugar)
(6.02x1023 molecs sugar)(2.5 mole sugar)
(1molsugar)(X) (1.505x1024molecsmols sugar)
X 1.51x1024 molecules of sugar
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• What if I asked you how many atoms are in a mole
  of a compound?
• you must know how many atoms are in a
  representative particle or cluster of the
  compound.
• To do this you must know the chem formula
• For example, each molecule of CO2 is composed of
  1 C 2 Os 3 atoms
• 1 mole of carbon dioxide molecules contains
  avogadros number of carbon dioxide molecules.
• Thus a mole of CO2 contains three times
  avogadros number of atoms

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Using the mole in calculations 3

• To find the of atoms in a mol of a compound,
• You 1st determine the of atoms in a
  representative particle of that compound
• And then multiply that of atoms by avogadros

How many atoms of carbon are in 2.12 mols of
propane molecules (C3H8)?
Useful Info 1 mol C3H8 6.02x1023 molecules
C3H8 1molecule C3H8 3 atoms of C
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1st we need to see how many molecules of propane
we have if we have 2.12 moles.
1 mole C3H8
2.12 moles C3H8
6.02x1023molec C3H8
X molec C3H8
(1molecC3H8)(X)(1.276x1024molecmolsC3H8)
X 1.276x1024 molecules of C3H8
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2nd we need to see how many atoms of C if we have
1.276x1024 molecs of C3H8.
1 molecule C3H8
1.276x1024 molec C3H8
3 atoms of C
X atoms C
(1molec C3H8)(X)(3.83x1024molec atoms C)
X 3.83x1024 atoms of Carbon
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How we measure moles

• Do you know how to measure out 3 moles of sugar
  or salt or water?
• The mole is a counting unit, so we would have to
  count out 6.02x1023 particles of each substance.
  (no thank you)
• There are 2 ways we can use to measure out a
  number of moles of a substance.
• Measure it in grams (a mass)
• Or measure it in liters (a volume)

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Using mass to measure moles

• One of the units we can use to measure out a
  particular amount of moles is to weigh it out in
  grams?
• The only problem with this method is that 1 mol
  of books will weigh more than 1 mol of pencils,
  since each book is heavier.
• What if 1 mol of pencils weighs 500Gtons and 1
  mol of books weighs 1x106Gtons.
• How much would 3.0 mols of pencils and 3 mols of
  books weigh?
• 500 Gtons 3 mols 1500 Gtons pencils
• 1x106 Gtons 3 mols 3x106 Gtons

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Using mass to measure moles

• To be able to measure out 1 mol of a substance we
  would need access to the known mass in grams of 1
  mol of any substance in question
• We would need a data table that provided all of
  these masses since every substance involved would
  have its own mass.
• Remember, we dont use the mole to count anything
  but atoms, molecules, etc.
• So we need a table that provides the mass 1 mole
  would weigh for every combination of atoms known
  to man.

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Using mass to measure moles

• It just so happens that the periodic table
  provides us with some of that information.
• The masses of each atom on the table is the
  equivalent to the mass of 1 mole of that atom
• Every type of atom known to humankind is on that
  table.
• The mass on the periodic table is called the
  molar mass (units of g/mol), because it
  represents the mass of 1 mol of that atom
• 1 mole of Mg atoms weighs 24.305 g
• 1 mole of C atoms weighs 12.011 g

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Using mass to measure moles

• That works well for atoms off of the periodic
  table, but how do we deal the molar masses of
  molecules and compounds?
• Each of those compounds and molecules is composed
  of a combination of atoms
• We have the molar masses for all of the atoms on
  the periodic table
• We need to be able to add up the total weight of
  all of the atoms in the compound or molecule
  given its formula.
• For ex, what is the molar mass of H2O?

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• We just add the molar masses of each of the atoms
  that make up the molecule
• From the PT, we find that the molar mass of 1
  mole of Hydrogen atoms is 1.0079 g.
• We have 2 Hydrogen atoms per molecule of H2O, so
  our Hydrogen atoms total 2 1.0079 g or 2.0158
  g per mole
• The mass of 1 mole of oxygen atoms is 15.999 g.
• We have only 1 atom of oxygen per mole-cule of
  H2O so our total mass of oxygen is 1 15.999 g
  or just 15.999 g per mol
• Therefore 1 mole of H2O molecs would weigh,
  2.0158g15.999g 18.0148g

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Ex 2 Calculating molar masses using chemical
formulas
What is the mass of 1 mole of C6H12O6?

• The overall mass of 1 mole of C6H12O6 will be the
  molar mass of 6 Carbons the molar mass of 12
  Hydrogens the molar mass of 6 Oxygens.

6 Carbons
12.011 g
6
72.066 g
12 Hydrogens
1.0079 g
12
12.095 g
6 Oxygens
15.999 g
6
95. 994 g
180.16 g/mole
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• Even though for compounds and molecules we have
  to calculate a molar mass using the periodic
  table, they are considered given or known values.
• We can use these molar masses in calculations in
  which we are either give moles and asked for its
  mass equivalent or given mass and asked for its
  mole equivalent.
• If we are given an element we just use the mass
  from the periodic table
• If we are given a formula instead we just
  calculate the molar mass of the molecule using
  the masses from the periodic table.

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Using the mole in calculations 4

• How much would
• 9.45 moles of N2O3 weigh?

1 mole N2O3
9.45 moles N2O3
2(14.007g)3(15.999g)
X g N2O3
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Using the mole in calculations 4

• How much would
• 9.45 moles of N2O3 weigh?

1 mole N2O3
9.45 moles N2O3
76.011g N2O3
X g N2O3
(1mole N2O3)(X g N2O3)
(9.45 moles N2O3)(76.011g N2O3)
(1mol N2O3)(X) (718 g mols N2O3)
X 718 grams of N2O3
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Using the mole in calculations 5
We have 92.2g of FeO, how many moles is the
equivalent of the given mass?
1 mole FeO
X mols FeO
1(55.847g)1(15.999g)
92.2 g FeO
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Using the mole in calculations 5

• We have 92.2g of FeO, how many moles is the
  equivalent of the given mass?

(71.846g FeO)(X mols FeO)
(1 mole FeO)(92.2 g FeO)
(71.846gFeO)(X) (92.2 gmols FeO)
X 1.28 moles of FeO
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Using volume to measure moles

• The other unit we can use to measure out mols is
  to measure a gas in Liters
• There is a standard volume that 1 mol of any gas
  will occupy called molar volume.
• If we had 1 mol of Ne and 1 mol of CO2 they would
  each contain 6.02x1023 particles, and occupy the
  same volume under standard conditions (0C, 1
  atm).
• At STP or standard temp press 1 mol of any gas
  occupies 22.4 Liters of space
• 1 mol of He 22.4 L of space
• 1 mol of N2 22.4 L of space

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Using the mole in calculations 6

• What volume, in Liters, would .500 mols
  of CO gas occupy at STP?

Remember 1 mol CO 22.4 L CO
1 mole CO
.500 mol CO
22.4 L CO
X L CO
(1mol CO)(X L CO) (.500 mol CO)(22.4 L CO
X 12.2 L of CO
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Using the mole in calculations 7

• If you have a 35.67g piece of Chromium
  metal on your car, how many atoms of
  Chromium are in this piece of metal?

• You are given mass and asked for number of
  particles
• Lets get some strategy

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• Its going to take us 2 conversions, we just need
  to follow the arrows

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• 1st we must convert our given mass of Chromium to
  moles of Chromium
• So we need to use the periodic table to calculate
  the mass of 1 mole of Chromium

1 mole Cr
X mol Cr
51.996g Cr
35.67g Cr
(51.996gCr)(X mol Cr)
(35.67gCr)(1 mol Cr)
X .6860 mol Cr
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• 2nd we must convert our newly found moles of Cr
  to atoms of Cr
• So we need to remember that 1 mole of anything
  there are 6.02x1023 particles

X atoms Cr
6.02x1023 atoms Cr
1 mole Cr
.6860 mol Cr
(1 mol Cr)(X atoms Cr)
(6.02x1023 atoms Cr) (.6860 mol Cr)
X 4.13x1023 atoms Cr