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Welcome to the Periodic Table

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However, atoms & molecules are extremely small ... 1 mole (6.02x1023) of donut holes would cover the earth and would be 5 miles deep. ... – PowerPoint PPT presentation

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Title: Welcome to the Periodic Table


1
THE MOLEUnit 7
2
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

3
  • 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.

4
  • 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)

5
CHEMICAL
REP. PARTICLE
REPRESENTATIVE
SUBTANCE
FORMULA
PARTICLE
IN 1 MOL
6
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

7
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
8
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
9
  • 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

10
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
11
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
12
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
13
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)

14
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

15
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.

16
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

17
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?

18
  • 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

19
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
20
  • 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.

21
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
22
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
23
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
24
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
25
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

26
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
27
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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

32
  • 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
33
  • 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
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