2Counting AtomsEverything we’ve done so far in chemistry has dealt with individual atoms or moleculesHowever, it isn’t practical to work with 1 atom or 1 molecule or even 1,000,000 atoms or moleclesThey are just too small!Therefore, chemists don’t work with atom or even 1,000,000 atoms, they work with a huge collection of atoms
3Counting AtomsIt is impractical to get caught up into working with 1 atom or 1 atom’s mass.It makes more sense to work with a collection of atoms rather than individuallyScientists were challenged to figure out a way to define a universal collection of particlesAnd which could still be described in terms of a relative mass
4Counting AtomsWe’ve already got the periodic table with masses for each elementSo how many atoms are in that collection (assuming gram masses)That number of atoms would immediately connect all other atoms and give us measurable amountsOxygen:
6Counting AtomsThe number of atoms that are in the gram mass on the PT is called Avogadro’s NumberAnd is defined as 1 moleThe mole becomes a counting unit much like the dozen.1 dozen eggs = 12 eggs1 mole of eggs =602,000,000,000,000,000,000,000eggs
7Counting Atoms 1 mole is always = 6.02 x 1023 items The word “mole” was introduced by Wilhelm Oswald, who derived the term from the word moles meaning a “heap” or “pile.”We are just defining the pile as con-taining 6.02x1023 itemsAny time we are counting how many we have and we want to describe it in terms of moles than…1 mole is always = 6.02 x 1023 items
8Counting AtomsThe mole, whose abbreviation is “mol”, is the SI base unit for measuring amount of a pure substance.It’s used exclusively for counting atoms, molecules, ions, or other things that are extremely smallIt’s the chemist’s six-pack or dozen. Many objects in our everyday lives come in similar counting units.1 ream = 500 sheets of paper1 pair of socks = 2 socks1 cube = 24 cans
9Counting AtomsWe will learn in the near future that when a chemist reasons through a chemical reaction (recipe) they think in terms of X number of mols of this compound reacts with Y number of mols of this compound.So we need to know how to calculate the number of molecules or atoms are involved in that X number of mols
10How many moles is equivalent to 1.355x1024 atoms of Au? Counting AtomsUsing the mole in calculations #1How many moles is equivalent to 1.355x1024 atoms of Au?unit equality:1 mol Au = 6.02 x 1023 atoms Au
11Counting Atoms = 2.251 mol Au The desired conversion is: atoms moles 1 mole Au1.355x1024 atoms Au6.02x1023atoms Au= mol Au
12Counting Atoms Using the mole in calculations #2 How many molecules of carbon dioxide is mols?unit equality:1 mol CO2 = 6.02x1023 molecules of CO2
13Counting Atoms = 2.15x1022 molecules CO2 The desired conversion is: moles atoms6.02x1023molecules CO2mols CO21 mole CO2= 2.15x1022 molecules CO2
14Your Turn: 0.0753 mols of Na to atoms Make the following mole conversions using dimensional analysismols of Na to atoms2.55x1025 molecules of CO2 to mols1.89x1019 molecules of H2O to mols1.25 mols of O2 to molecules
15Counting AtomsNow suppose you want to determine how many atoms are in a mol of a compound or moleculeTo do this you must know how many atoms are involved in the molecule.To determine the number of atoms represented in a molecule requires knowing the chemical formulaEg, each molecule of Carbon Dioxide (CO2) is composed of 3 atoms
16How many atoms of Carbon are in 2.12 mols of Propane (C3H8)? Counting AtomsUsing the mole in calculations #3How many atoms of Carbon are in 2.12 mols of Propane (C3H8)?unit equalities:1 mol C3H8 = 6.02x1023 molecules C3H81 molecule C3H8 = 3 atoms C
18Your Turn: How many atoms of Oxygen are there in 0.118 mols of CO2 Make the following mole conversions using dimensional analysisHow many atoms of Oxygen are there in mols of CO2How many atoms of Oxygen are there in Ca(NO3)2.
19Counting AtomsWe can’t literally count the number of atoms in a sample, but we can count them by massSo, there needs to be a connection between the mass of a sample and the number of moles in that sampleIf we weigh out a particular mass of a substance, that can represent a particular number of molsIf we weighed out g of CarbonIt will represent 1 mole of Carbon and/or 6.02x1023 Carbon atoms
2018.99g F atoms=1 mol F atoms=6.02x10 F atoms Counting AtomsThis allows us to use the mass off of the periodic table to represent the mass of 1 mole (or 6.02x1023 atoms) of that element1 mol of C atoms weighs g1 mol of H atoms weighs g1 mol of W atoms weigh g18.99g F atoms=1 mol F atoms=6.02x10 F atoms23
21Counting AtomsThis new understanding of mass from the periodic table is known as the gram molar mass, or molar mass.Molar Mass = mass of 1 mole of atoms in gramsWe have a list of every possible molar mass for any given element on the periodic tableThis mass can be used as a conversion factor…1 mole = g H, etc.
22Counting Atoms So what if we have a compound instead of an element? How do we figure out the mass of a mole of a compound?This would be called a molecular mass, formula mass, or still can be called a molar massAll we need is the formula for a representative particle of the compound and the periodic table.
23Counting AtomsFor instance how do we calculate the mass of 1 mole of Ca(OH)2?You can calculate the mass of a mol- ecule of Ca(OH)2 by breaking it up into individual piecesWe can start with Calcium, then 2 O’s, then 2 H’s…until we run out of piecesCa: (1)(40.09 g/mol) =40.09O: (2)(15.99 g/mol) =H: (2)(1.008 g/mol) =74.09 g/mol
246.02x1023 molecules of the compound –weighs 180.1 grams Counting AtomsWhat is the MM of glucose (C6H12O6)?(6C’S)(12.011g/mol) =72.066g/mol(12H’S)(1.008 g/mol) =12.096g/mol(6O’S)(15.99 g/mol) =95.94g/mol180.1g/mol1 mole of C6H12O6 or6.02x1023 molecules of the compound –weighs grams
25Practice Time: C9H20 (NH4)2CO3 Zn(C2H3O2)2 CCl4 Calculate the molar mass of each of the formulasC9H20(NH4)2CO3Zn(C2H3O2)2CCl4
26How many grams are in 9.45 mol of Dinitrogen Trioxide (N2O3) Counting AtomsUsing the molar mass in calculations:How many grams are in 9.45 mol of Dinitrogen Trioxide (N2O3)The only connection to N2O3 and its mass is how much 1 mol of the compound weighs. But, using it as a comparison we can calculate the mass of 9.45 mol.
27Counting Atoms Step 1: Determine the mass of 1 mol of N2O3 (2N’s)(14.01g) =28.02g(3O’s)(15.99g) =47.97g75.99gIf 1 mole of N2O3 weighs 75.99g than how much will 9.45 mols of N2O3 weigh?
28Counting Atoms 75.99 g N2O3 9.45 mol N2O3 1 mol N2O3 =718 g N2O3 Step 2: Convert the given moles to grams using the Molar mass equality.75.99 g N2O39.45 mol N2O31 mol N2O3=718 g N2O3
29Counting Atoms Find the number of moles of 92.2g of Iron (III) Oxide (Fe2O3)The only connection to the mass of Fe2O and how that corresponds to mols is how that 1 mol of the compound weighs a certain # of grams. Using that we can figure out how many moles weigh 92.2 g
30Counting Atoms (2Fe’s)(55.85g) = 111.7g (3O’s)(15.99g) = 47.97g Step 1: Determine the mass of 1 mol of Fe2O3(2Fe’s)(55.85g) =111.7g(3O’s)(15.99g) =47.97g159.67gIf 1 mole of Fe2O3 weighs g than how many mols will weigh 92.2 g of Fe2O3?
31Counting Atoms 1 mol Fe2O3 92.2 g Fe2O3 159.67 g Fe2O3 =.577mol Fe2O3 Step 2: Convert the given mass to mols using the Molar mass equality1 mol Fe2O392.2 g Fe2O3g Fe2O3=.577mol Fe2O3
32Practice Time: Determine the number of mols of CO2 in 454 grams. What is the mass of mols of propane gas, C3H8?How many mols of methane molecules, CH4, are in grams of methane?How many grams does x10-5 mols of Na2CO3 weigh?
33Counting AtomsAnother generality about the mole is that with matter in the gas phase we can develop another equality.Under the same conditions, equal volumes of gases contain equal numbers of particles.1 mol of a gas will occupy the same volume as 1 mol of any other gas under the same conditions.
34Molar Volume of a Gas22.4 L22.4 L1 mole of any gas under the specific conditions of 0°C and 1 atm (STP) will occupy a volume of 22.4 L.6.02x1023molecules of O26.02x1023molecules of CO2
35What volume, in Liters, does 0.60 mol of SO2 gas occupy at STP? Counting AtomsWhat volume, in Liters, does 0.60 mol of SO2 gas occupy at STP?The only connection to the volume of any gas and how that corresponds to mols is that 1 mol of a gas occupies 22.4 Liters of space. Using that we can figure out the volume of 0.60 mols of a gas at STP.
36Counting Atoms 22.4 L SO2 0.60 moles SO2 1 mole SO2 = 13 L SO2 Step 1: Use the equality 1 mol = 22.4 L to do the conversion22.4 L SO20.60 moles SO21 mole SO2= 13 L SO2
37Practice Time:What volume is occupied by mols of nitrogen gas at STP?How many moles of gas would be in 15,000 L of air?
39Counting AtomsAspartame is an artificial sweetener that is 160 times sweeter than sugar when dissolved in water. It is marketed as Nutra-Sweet (C14H18N2O5).What number of molecules are in 5.0 mg of aspartame?What number of atoms of nitrogen are in 1.2 g of aspartame?What is the mass in g of 1 molecule of aspartame?
42Your Turn:What is the mass of 7.21x1021 molecules of silver acetate (AgC2H3O2)?How many grams of neon gas will fill a room with a volume of 4000L at STP?How many molecules are there in g of Cu(NO3)2?Which has the greater mass?a. 9.5x1024 atoms of Cb. 2.1 mol Br2c. 1.86x1022 molecules of CCl4d. 59.5g Hg