1 The Mole

2 Counting Without Counting If you had to count the number of coffee beans in this bag how would you do it? How long would it take?

3 Counting Without Counting If you had to count the number of grains of sand in this bag how would you do it? How long would it take ? How do scientists count atoms or molecules?

4 Let’s try to come up with a way to count the number of beans in a large bag of beans without actually counting them all and without taking a long time. Eventually we want to apply this new method of counting to counting atoms! Any IDEAS?

5 Counting by Weighing Weight of 10 beans _____ g Average weight of one bean _____ g Weight of all beans in bag _____ g Weight of beans in bag _____ (g) 1 bean = _____ beans in a _____ (g) bag Counting by weighing works when the items are all about the same size and mass. The closer the items are to being exactly the same, the more accurate the method is. If the beans were all exactly the same we would only have to weigh one and not take the average of ten!

6 Counting by Weighing What was the key information needed to determine the number of beans in any bag of beans without counting them all? The average mass of ONE bean!

7 Applying “Counting by Weighing” to Atoms How can we use this idea to determine the number of atoms per gram of the element carbon? We need to know the mass of one atom of carbon! We can’t weigh an atom of carbon directly but we do know something about the particles that make up a carbon-12 atom. proton = 1.67 x g Carbon-12 has 6 protons neutron = 1.67 x g Carbon–12 has 6 neutrons electron = too small to count Carbon-12 has 6 electrons (still too small)

8 Mass of one Carbon Atom

9 Applying “Counting by Weighing” to Atoms So one atom of Carbon-12 weighs about 2.0 x g. How many grams of carbon should we use? (like the total mass of an beans bag). Weight for one carbon atom is a result of 12 particles (6p+6n). So let’s use 12 GRAMS of carbon. (Who is this guy?)

How Many Atoms in 12 Grams of Carbon How many atoms do you think are in 12 grams of carbon? Let’s use dimensional analysis (canceling units) to figure it out! 12gC 1 atom C = 6.0 x atoms of carbon 2.0x gC That’s 600,000,000,000,000,000,000,000 atoms!! OK, Why Carbon? 10

11 Oxygen and Hydrogen Were Also Both Used as Mass Standards Physicists used Hydrogen Chemists used Oxygen Because oxygen and hydrogen both have isotopes the scales didn’t agree, but the ratio of two elements was the same. Because oxygen and hydrogen both have isotopes the scales didn’t agree, but the ratio of two elements was the same. Physicists and Chemists compromise to Carbon as the mass standard in Physicists and Chemists compromise to Carbon as the mass standard in Can you believe it took them that long to agree!!

12 The Mole Now let’s go backwards using oxygen with that 6 x number of atoms for 12 grams of carbon 6.0 x atoms 2.68 x g = 16 g oxygen!! oxygen 1 atom oxygen look familiar?

13 The Mole 6.0 x is a pretty special number. It’s called “a mole” 1 “Mole” represents 6.0 x of anything. Like 1 dozen = 12 of anything (Other examples?) One mole of beans is 6.0 x beans. The mole is based on the number of atoms in 12 grams of carbon-12

The Mole Scientists have determined that One Mole = 6.02 x atoms. It’s important in chemistry because its used to convert grams to atoms. Scientists want to react atoms with atoms but they can’t count out atoms directly, they’re too small. Using The Mole scientists can weigh out a number of grams of a chemical and calculate the number of atoms present in that mass! 14

15 “The Mole” (or mol) may come from a shortening of “molecule”. Also the word “mole” is Latin for “heap or pile” Avogadro didn’t coin the term, he wasn’t even the first to recognize how to calculate the number. Loschmidt, a school teacher, was the first to calculate atoms/mole and his work was based on Avogadro’s work. Loschmidt (1865) Avogadro (1811) Avogadro suggested that equal volumes of all gases at the same temperature and pressure contain the same number of molecules.

16 The Mole 6.02 x atoms of carbon-12 is grams, and 6.02 x atoms of oxygen-16 weighs grams … So the mole is clearly related to an element’s atomic mass. Let’s define one mole of any element as equal to the atomic mass (weighted average of isotopes) of that element.

What is a Mole 17 atomic mass of 1 mole of atoms 6.02 x atoms element of any element of any element 1 mole of carbon = 12.01g carbon = 6.02 x atoms C 1 mole of oxygen = 16.00g oxygen = 6.02 x atoms O 1 mole of sodium = 23.00g sodium = 6.02 x atoms Na ==

18 How Big is a Mole (6.02 x ) ? If you count out loud starting with the number "one" at the rate of one count every second, it would take you 1,909,577,942,668,696 years to finish. Using a 2 GHz CPU, it will still take about 2,243,506 years to “count” to 1 mole. One mole of beans would cover the earth 25 miles thick!!

19 Using “The Mole” Once you understand the concept of “The Mole” it’s easy to use. Now that we know the mole REPRESENTS the number of particles we can use the mole directly. Calculate the number of moles in g of copper: g Cu 1 mole Cu = 2.4 moles of Cu g Cu Calculate the number of atoms in 20.4g of carbon: g C 1 mole C 6.02 x atoms C = 1.02x10 24 atoms C g C 1 mole C

20 Bad Mole Jokes

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22 The Original Wack-a-Mole

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A small furry mammal walks into a bar and orders a drink. The bartender says, "Sorry, our maximum occupancy is only 5.99 x We can't serve a mole." 26

"Do you have mole problems? If so, call Avogadro at " 27

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31 More Practice with the Mole How many moles of Zinc are in 50.0g of Zinc metal? How many particles of chlorine gas are there in 20 moles of chlorine gas?

32 More Practice with the Mole How many moles of Zinc are in 50.0g of Zinc metal? 50.0 g Zn 1 mole Zn = Moles Zn g Zn How many molecules of chlorine gas are there in 20 moles of chlorine gas? 20 moles Cl x molecules Cl 2 = 1.2x10 25 Molecules Cl 2 1 mole Cl 2

Even More Practice!! How many moles of NaCl are in 50.0g of sodium chloride? = Moles NaCl Na = 23.00g/mole (atomic mass) Cl = 35.45g/mole (atomic mass) NaCl = g/mole (molar mass) g NaCl mole NaCl g NaCl 0.855