Bellwork 10/21 What does 1 mole of Eagle football equal? What kind of conversions use Avogadro’s number? How many moles of selenium are in 5.20 x atoms of selenium? How many atoms of molybdenum are in 6.35 moles of molybdenum?

Word Wall Mole (mol) Avogadro’s number

Chapter 3 Part II where things get fun around here!

Is it practical to measure each grain of sand? How else might you measure or quantify the sand?

Let’s try it… Paper clips…the triple beam balance… And YOU! Please make groups of 3 or 4. You need a handout and a sample of paperclips. You’ll have to share the balances.

Sand isn’t the only thing too small to count… Atoms are too!

Learning Targets: Review dimensional analysis to convert units. Describe how Avogadro’s number is related to a mole of any substance. Calculate the mass of a mole of any substance.

We live in a quantitative world. Quantities that answer “how much” or “how many”. Like the grade you got on your last test… or how many times you heard your favorite song… Chemistry is a quantitative science. Chemists need to know how many milligrams of elements or compounds combine to make fertilizer or paint… Pharmacists measure chemicals in medicine…

How do you measure matter? Songs on your playlist? Touchdowns? What about gasoline? Bananas or potatoes? Cough medicine? Soda?

Some units always indicate a specific number of items. A pair always means… A dozen always means… A baker’s dozen means… But think about apples.

Apples can be measured different ways… At a fruit stand… usually by count, right? (5 for $4) At Kroger… usually by weight/mass. ($1.95 a kg) At an orchard… by volume. ($12.00 a bushel) Each of these measurements can be equated to a dozen apples.

By count: 1 dozen apples = 12 apples By mass: 1 dozen apples = 2.0 kg apples By volume: 1 dozen apples = 0.20 bushel apples

The mole… 13

The mole is a measuring unit. In chemistry, we do calculations using a measuring unit called a mole. The mole is an SI unit (remember this one?!) that measures the amount of a substance. Just like a dozen… or a bushel… or a pair. 14

The mole can be related to the number of particles (a count), the mass, and the volume of an element or a compound just as a dozen was related to these three units for apples.

Let’s try some conversions with apples. 1.What is the mass of 90 average sized apples? Use the conversion factor : 1 dozen apples = 2.0 kg apples Number of apples  dozens  mass of apples

Analyze, Calculate… Evaluate Does the result make sense? Because a dozen apples has a mass of 2.0 kg and 90 apples is less than 10 dozen apples, the mass should be less than 20 kg of apples. (10 doz x 2.0 kg/doz) Try the practice problems in your notes.

Atoms are very, very, very small. Because they’re so darn small, it just isn’t practical to count them. Like our paper clips! But different… in many ways. Not like the paper clips much at all, actually… However! We can do something similar to counting paper clips… We can use a term that represents a specified number of particles. Voila! We need The Mole…

Dozen = 12 Pair = 2 The Mole (mol): A unit to count numbers of particles Ream of paper Baker’s dozen GrossFortnightGoogolByte

Mole = x Dozen = 12 Pair = 2 The Mole (mol): A unit to count numbers of particles Baker’s dozen Gross Donkey power FortnightGoogol

The mole is a counting unit… The mole is the SI unit for amount of substance. It’s abbreviation is mol.

Just as a dozen eggs represents 12 eggs, a mole (mol) of a substance represents x particles of that substance. This is Avogadro’s number. It is an experimentally determined number (based on Carbon-12, again!). It’s called Avogadro’s number in honor of Amedeo Avogadro di Quarengna ( ).

A mole (mol) of a substance represents x particles of that substance. A mole of carbon atoms is x10 23 carbon atoms. A mole of chemistry teachers is x10 23 chemistry teachers. 25

1 mole of M&Ms… 26

27 It's a lot easier to write the word 'mole' than to write 6.022x10 23 anytime you want to refer to a large number of things! Basically, that's why this particular unit was invented.

Just how big is that?! To get a sense of how large Avogadro’s number is, consider the following: If every person living on Earth (6.8 billion people) worked to count the atoms in one mole of an element, and if each person counted continuously at a rate of one atom per second, it would take about 3 million years for all the atoms to be counted.

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Total Recall: How do we put powers of 10 in our calculator in Chemistry class?

Conversions with Avogadro’s Number We use Avogadro’s number to find the number of atoms of an element or compound in moles Or To find the amount of an element or compound in moles from the number of atoms. Moles  atoms or atoms  moles 32

Example-1 with an element: How many moles of magnesium are in 1.25 x atoms of magnesium? Atoms  moles 1 mol Mg = x atoms of Mg

Let’s work some in small groups Textbook pg. 82 Check the sample problem then work #1 – 3. We’ll check them in large group.

Example with a compound: To determine how many atoms are in a mole of a compound, we have to look at the chemical formula of the compound. Each molecule of CO 2 has 3 atoms. A mole of CO 2 has 3 times Avogadro’s number of CO 2 molecules. A molecule of CO has _____ atoms and _____ times Avogadro’s number of CO molecules.

Let’s practice counting atoms… How many atoms are there in each compound: 1 molecule of NO 2 1 molecule of O 3 1 molecule C 8 H 8 O 4 1 molecule of C 12 H 22 O 11 = And just for fun… how many oxygen atoms are in each compound?

To find the number of atoms in a compound, you must determine the number of atoms that comprise the compound and multiply that number by Avogadro’s number.

Example 2: How many atoms are in 2.12 mol of propane (C 3 H 8 )? Moles  molecules  atoms

Now let’s practice in small group. There are practice problems in your notes. Work them in small groups and we’ll check them in large group.

What about going the other way? Example 3: How many moles are there in 4.65 x molecules of NO 2 ? MOL  atoms  mol

Show me!

Micro World atoms and molecules Macro World grams

The mole (mol) is the amount of a substance that contains as many particles as there are atoms in exactly grams of 12 C 1 mol = x Avogadro’s number (N A ) Molar mass is the mass of 1 mole of in grams eggs shoes cats

The answer is that moles give us a consistent method to convert between atoms/molecules and grams. It's simply a convenient unit to use when performing calculations. 45

Molar mass 1 mole 12 C atoms = x atoms = g 1 12 C atom = amu For any element atomic mass (amu) = molar mass (grams) atomic mass (amu) = molar mass (grams)

47 One Mole of: C S Cu Fe Hg

The molar mass of He is 4.00 g/mol. To find how many g of He there are in 2 moles of He, multiply by the molar mass mol He x 4.00 g He = 8.00 g He 1 mol He

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The abbreviation for mole is mol. Molar mass is the weight of one mole of a chemical compound. Molar mass is usually written in units g/mol. 51

Section 3 Counting Atoms Sample Problem B What is the mass in grams of 3.50 mol of the element copper, Cu? Chapter 3

Section 3 Counting Atoms Relating Mass to Numbers of Atoms, continued Sample Problem B Solution, continued The molar mass of copper from the periodic table is rounded to g/mol. Chapter 3

Section 3 Counting Atoms Relating Mass to Numbers of Atoms, continued Sample Problem C A chemist produced 11.9 g of aluminum, Al. How many moles of aluminum were produced? Chapter 3

Section 3 Counting Atoms Relating Mass to Numbers of Atoms, continued Sample Problem C Solution Given: 11.9 g Al Unknown: amount of Al in moles Solution: Chapter 3 The molar mass of aluminum from the periodic table is rounded to g/mol.

Section 3 Counting Atoms Relating Mass to Numbers of Atoms, continued Sample Problem D How many moles of silver, Ag, are in 3.01  atoms of silver? Chapter 3

Section 3 Counting Atoms Relating Mass to Numbers of Atoms, continued Sample Problem D Solution Given: 3.01 × atoms of Ag Unknown: amount of Ag in moles Solution: Chapter 3

Section 3 Counting Atoms Relating Mass to Numbers of Atoms, continued Sample Problem E What is the mass in grams of 1.20  10 8 atoms of copper, Cu? Chapter 3

Section 3 Counting Atoms Sample Problem E Solution Given: 1.20 × 10 8 atoms of Cu Unknown: mass of Cu in grams Solution: Relating Mass to Numbers of Atoms, continued Chapter 3 The molar mass of copper from the periodic table is rounded to g/mol.

60 In chemistry there are many different concepts of mass… We need to talk about 3 of them.

First, atomic mass… Isotopes are atoms of the same element (and so with the same number of p+ and e-) but with different masses due to having different numbers of n 0. Right? 61

The mass of an atom is incredibly small and it doesn’t make sense to use units like grams to measure it… It’s easier to measure it in atomic mass units. 62

Scientists like a standard… Scientists set up a scale of atomic mass, one atom was arbitrarily chosen as the standard. Carbon-12 Chemists use this standard to compare units of atomic mass. It’s a relative scale… relative to C

Atomic mass unit It is defined as the mass equal to 1/12 th the mass of one C-12 atom. Or amu… (our textbook uses just plain “u”) 64

By definition: 1 atom 12 C “weighs” 12 amu On this scale 1 H = amu 16 O = amu 16 O = amu Atomic mass is the mass of an atom in atomic mass units (amu)

Micro World atoms and molecules Macro World grams

The answer is that moles give us a consistent method to convert between atoms/molecules and grams. It's simply a convenient unit to use when performing calculations. 67

The mole (mol) is the amount of a substance that contains as many particles as there are atoms in exactly grams of 12 C 1 mol = x Avogadro’s number (N A ) Molar mass is the mass of 1 mole of in grams eggs shoes cats

69 A mole of carbon atoms is 6.02x10 23 carbon atoms. A mole of chemistry teachers is 6.02x10 23 chemistry teachers.

1 mole of M&Ms… 70

71 It's a lot easier to write the word 'mole' than to write '6.02x10 23 ’ anytime you want to refer to a large number of things! Basically, that's why this particular unit was invented.

The abbreviation for mole is mol. Molar mass is the weight of one mole of a chemical compound. Molar mass is usually written in units g/mol. 72

Molar mass 1 mole 12 C atoms = x atoms = g 1 12 C atom = amu For any element atomic mass (amu) = molar mass (grams) atomic mass (amu) = molar mass (grams)

74 One Mole of: C S Cu Fe Hg

The molar mass of He is 4.00 g/mol. To find how many g of He there are in 2 moles of He, multiply by the molar mass mol He x 4.00 g He = 8.00 g He 1 mol He

Conversions with Avogadro’s Number We use Avogadro’s number to find the number of atoms of an element in moles Or To find the amount of an element in moles from the number of atoms. 76

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Section 3 Counting Atoms Sample Problem B What is the mass in grams of 3.50 mol of the element copper, Cu? Chapter 3

Section 3 Counting Atoms Relating Mass to Numbers of Atoms, continued Sample Problem B Solution, continued The molar mass of copper from the periodic table is rounded to g/mol. Chapter 3

Section 3 Counting Atoms Relating Mass to Numbers of Atoms, continued Sample Problem C A chemist produced 11.9 g of aluminum, Al. How many moles of aluminum were produced? Chapter 3

Section 3 Counting Atoms Relating Mass to Numbers of Atoms, continued Sample Problem C Solution Given: 11.9 g Al Unknown: amount of Al in moles Solution: Chapter 3 The molar mass of aluminum from the periodic table is rounded to g/mol.

Section 3 Counting Atoms Relating Mass to Numbers of Atoms, continued Sample Problem D How many moles of silver, Ag, are in 3.01  atoms of silver? Chapter 3

84 (uranium compound) Types of radioactivity uranium compound

(uranium compound) Types of radioactivity

The Bohr Model of the Atom Niels Bohr (1922 Nobel Prize in Physics)

Thus one mole of ethyl alcohol, C 2 H 6 O, weighs g. One mole of water weighs g. If we mix g of ethyl alcohol with g of water, we can be assured that the mixture contains 1 molecule of ethyl alcohol per molecule of water. Further, we will know that there are 2 atoms of C and 8 atoms of H per each 2 atoms of O. Thus the mole allows us to weigh convenient amounts of material containing known numbers of atoms; i.e., it allows us to count atoms. 87

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YV1s YV1s Molar eclipse of the heart XP0 91

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93 In chemistry there are many different concepts of mass… We need to talk about 3 of them.

First, atomic mass… Isotopes are atoms of the same element (and so with the same number of p+ and e-) but with different masses due to having different numbers of n 0. Right? 94

The mass of an atom is incredibly small and it doesn’t make sense to use units like grams to measure it… It’s easier to measure it in atomic mass units. 95

Scientists like a standard… Scientists set up a scale of atomic mass, one atom was arbitrarily chosen as the standard. Carbon-12 Chemists use this standard to compare units of atomic mass. It’s a relative scale… relative to C

Atomic mass unit It is defined as the mass equal to 1/12 th the mass of one C-12 atom. Or amu… (our textbook uses just plain “u”) 97

By definition: 1 atom 12 C “weighs” 12 amu On this scale 1 H = amu 16 O = amu 16 O = amu Atomic mass is the mass of an atom in atomic mass units (amu)

Compare that to average atomic mass The average atomic mass of an element is the weighted average of the masses of its isotopes on this scale… Just like how your grades are weighted. 99

Average atomic mass This is the number you see on the periodic table. 100

Average atomic mass We have to consider that most elements occur naturally as a mixture of isotopes. Scientists determine the average mass of a sample of an element’s isotopes by determining the percentages of each of the isotopes and then giving the proper weight to each value. (Just like your grades!) 101

Dozen = 12 Pair = 2 The Mole (mol): A unit to count numbers of particles Ream of paper Baker’s dozen GrossFortnightGoogolByte

Mole = x Dozen = 12 Pair = 2 The Mole (mol): A unit to count numbers of particles Baker’s dozen Gross Donkey power FortnightGoogol

Elements rarely occur as only one isotope. They exist as mixtures of different isotopes of various masses. This way, the less common isotopes are accounted for. 104

Don’t confuse mass number with average atomic mass. Mass number is the mass of one particular atom. Average atomic mass is the average mass of a group of atoms of the same element that takes into consideration all the isotopes. 105

The average atomic mass of an element depends of both the mass and relative abundance of each of the element’s isotopes. 106

The average atomic mass is the weighted average of all of the naturally occurring isotopes of the element. Isotope Percent Abundance Isotopic Mass, amu 12 C 98.90% C 1.10%

How do we find atomic mass (average atomic mass)? The average atomic mass of an element depends of both the mass and relative abundance of each of the element’s isotopes. 108

Copper consists of 69.15% copper-63, which has an atomic mass of amu, and 30.85% copper-65, which has an atomic mass of amu. Calculate the average atomic mass for Cu.

Calculating average atomic mass Step 1: multiply the atomic mass of each isotope by its relative abundance. Step 2: add the results x amu x amu = amu** *Our textbook is going to round to 2 decimal places. 110

Average Atomic Mass Oxygen has three naturally occurring isotopes in the following proportions: O % ( amu); O % ( amu); O % ( amu). What is the average atomic mass of oxygen?

Let’s take it to 2 decimal places 1) x = ) x = ) x = amu 112

Next up… 113

Atoms are very, very small. For example, 1 atom of H weighs approximately 1.67 x kg. 114

Dozen = 12 Pair = 2 The Mole (mol): A unit to count numbers of particles Ream of paper Baker’s dozen GrossFortnightGoogolByte

Mole = x Dozen = 12 Pair = 2 The Mole (mol): A unit to count numbers of particles Baker’s dozen Gross Donkey power FortnightGoogol

Micro World atoms and molecules Macro World grams

The answer is that moles give us a consistent method to convert between atoms/molecules and grams. It's simply a convenient unit to use when performing calculations. 118

The mole (mol) is the amount of a substance that contains as many particles as there are atoms in exactly grams of 12 C 1 mol = x Avogadro’s number (N A ) Molar mass is the mass of 1 mole of in grams eggs shoes cats

120 A mole of carbon atoms is 6.02x10 23 carbon atoms. A mole of chemistry teachers is 6.02x10 23 chemistry teachers.

1 mole of M&Ms… 121

122 It's a lot easier to write the word 'mole' than to write '6.02x10 23 ’ anytime you want to refer to a large number of things! Basically, that's why this particular unit was invented.

The abbreviation for mole is mol. Molar mass is the weight of one mole of a chemical compound. Molar mass is usually written in units g/mol. 123

Molar mass 1 mole 12 C atoms = x atoms = g 1 12 C atom = amu For any element atomic mass (amu) = molar mass (grams) atomic mass (amu) = molar mass (grams)

125 One Mole of: C S Cu Fe Hg

The molar mass of He is 4.00 g/mol. To find how many g of He there are in 2 moles of He, multiply by the molar mass mol He x 4.00 g He = 8.00 g He 1 mol He

Conversions with Avogadro’s Number We use Avogadro’s number to find the number of atoms of an element in moles Or To find the amount of an element in moles from the number of atoms. 127

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Section 3 Counting Atoms Sample Problem B What is the mass in grams of 3.50 mol of the element copper, Cu? Chapter 3

Section 3 Counting Atoms Relating Mass to Numbers of Atoms, continued Sample Problem B Solution, continued The molar mass of copper from the periodic table is rounded to g/mol. Chapter 3

Section 3 Counting Atoms Relating Mass to Numbers of Atoms, continued Sample Problem C A chemist produced 11.9 g of aluminum, Al. How many moles of aluminum were produced? Chapter 3

Section 3 Counting Atoms Relating Mass to Numbers of Atoms, continued Sample Problem C Solution Given: 11.9 g Al Unknown: amount of Al in moles Solution: Chapter 3 The molar mass of aluminum from the periodic table is rounded to g/mol.

Section 3 Counting Atoms Relating Mass to Numbers of Atoms, continued Sample Problem D How many moles of silver, Ag, are in 3.01  atoms of silver? Chapter 3

135 (uranium compound) Types of radioactivity uranium compound

(uranium compound) Types of radioactivity

The Bohr Model of the Atom Niels Bohr (1922 Nobel Prize in Physics)

Thus one mole of ethyl alcohol, C 2 H 6 O, weighs g. One mole of water weighs g. If we mix g of ethyl alcohol with g of water, we can be assured that the mixture contains 1 molecule of ethyl alcohol per molecule of water. Further, we will know that there are 2 atoms of C and 8 atoms of H per each 2 atoms of O. Thus the mole allows us to weigh convenient amounts of material containing known numbers of atoms; i.e., it allows us to count atoms. 138

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