1. Atomic Mass and The Mole

2. Topic: AMU’s & Atomic Mass
Unit: The Mole and Atomic Mass
Topic: AMU’s & Atomic Mass
Objectives: Day 1 of 3
To learn how we define 1 amu (atomic mass unit)
To learn how we derive atomic mass from amu (atomic mass unit)
To learn how atomic mass is calculated using the average natural abundance of isotopes

3. Quickwrite Answer one of the questions below 1-2 sentences:
1 light year (the distance light travels in a year) is equal to 9.5 trillion kilometers!!!!!!!!!! Why do you think we measure distances to nearby stars in light years and not kilometers?????
Consider the reaction below, In order to make one molecule of CO2 (g), each carbon atom needs how many molecules of oxygen gas????
C(s) O2 (g)  CO2 (g)

4. 1 Atom reacts with 1 Molecule to yield 1 Molecule
Atomic Mass
The balanced Chemical equation for the reaction of solid carbon and gaseous oxygen to form gaseous carbon dioxide is as follows:
Now suppose you have a small pile of carbon, and you want to know how many oxygen molecules are required to convert all this carbon into carbon dioxide
The balanced equation tells us that one oxygen molecule (O2) is required for each carbon atom (C)
C(s) O2 (g)  CO2 (g)
1 Atom reacts with 1 Molecule to yield 1 Molecule

5. 1 Atom reacts with 1 Molecule to yield 1 Molecule
Atomic Mass
To determine the number of oxygen molecules required, we must know how many carbon atoms are present in the pile of carbon
But individual atoms are to small to see
We can easily count things like jelly beans and pennies, but atoms are far too small to be counted
C(s) O2 (g)  CO2 (g)
1 Atom reacts with 1 Molecule to yield 1 Molecule

6. Atomic Mass The mass of one proton in a carbon atom is
1.66 x grams
You can’t exactly put a carbon proton on a scale and weigh it
To simplify things, and to avoid using very small complex numbers like 1.66 x grams, scientists have defined a unit of mass called the atomic mass unit or amu for short
1 amu = 1.66 x grams or 1/12 the mass of a carbon atom

7. Atomic Mass
The mass of one carbon proton is equal to 1 amu or 1.66 x grams
Neutrons and protons weigh the same and electrons virtually have no mass or weight
So how many protons and neutrons does carbon have?
That’s right, 12, so carbon has 12 atomic mass units
Or, we say carbon has an average atomic mass of amu

8. What is Atomic Mass Unit (amu)?
A unit of mass equal to _____the mass of a carbon atom
1 amu = 1/12 the mass of a ______ atom or 1.66 x grams
It is a way to _______ the mass of a proton or ________
1/12
Answer Bank
average
1/12
simplify
Carbon
abundance
neutron
carbon
simplify
neutron

9. Atomic Mass A hydrogen atom is composed of one proton or 1 amu
Remember, neutrons and protons weigh the same and electrons virtually have no mass or weight
A helium has 2 protons and 2 neutrons
What is the average atomic mass for Helium?
That’s right, 4!

10. What is the average atomic mass for some common elements?
Hydrogen
1.008
Helium
4.00
Carbon
12.01
Nitrogen
14.01
Oxygen
16.00
Aluminum
26.98
Sodium
22.99

11. Atomic Mass The average atomic mass for carbon is 12.01 amu
Where does the 0.01 come from?
0.01 is the percent abundance in nature of the carbon isotopes
For example, if we weighed 12 grams of carbon, 0.01 percent is the amount of Carbon 14 and carbon 13 isotopes that exist in nature

12. Atomic Mass
Atomic Mass is the weighted average mass of the atoms in a naturally occurring element
It is based on AMU’s and the natural abundance of an elements isotopes

13. What is atomic mass?
The weighted _______ mass of the atoms in a naturally occurring element
It is based on AMU’s and the natural _________ of an elements isotopes
average
Answer Bank
average
1/12
simplify
Carbon
abundance
neutron
abundance

14. Mass of 100 natural carbon atoms = 100 atoms
Atomic Mass
Now that we know the average mass of a carbon atom, we can count carbon atoms by weighing samples of natural carbon
For example, let’s say you want to count out 100 carbon atoms
Because amu is the average atomic mass,
Mass of 100 natural carbon atoms = 100 atoms
12.01 amu
1 carbon atom
= 1,201 amu

15. Atomic Mass
Now let’s assume that when we weigh the pile of natural carbon mentioned earlier, the result is 3.00 x 1020 amu
How many carbon atoms are present?
We know that carbon has an average atomic mass of amu, so we can compute the carbon atoms using the following conversion factor
1 carbon atom = amu or
1 carbon atom
12.01 amu
3.00 x 1020 amu
1 carbon atom
= 2.50 x 1019
carbon atoms
12.01 amu

16. Practice:
Calculate the mass or weight in amu of a sample of aluminum that contains 75 atoms
75 aluminum atoms
26.98 amu
= 2,024 amu
1 aluminum atom

17. Practice:
How many aluminum atoms are present in a sample of aluminum that has a mass of 2,024 amu?
2,024 amu
1 aluminum atom
= 75 atoms
26.98 amu

18. Summarize: Why do scientist’s use AMU’s and light years???
What is the mass, in AMU of one nitrogen atom???
1 amu = 1/12 the mass of a _____ nucleus or _________ grams
______ _____ is the weighted average mass of the atoms in a naturally occurring element
It is based on AMU’s and the natural ______ of elemental isotopes

19. Unit: The Mole and Atomic Mass
Topic: The Mole
Objectives: Day 2 of 3
To understand the quantity of a mole
To understand the huge quantity of Avogadro’s number
To understand the mole mass relationship

20. Quickwrite Answer one of the questions below 1-2 sentences:
Your pencil uses graphite (pure carbon) to write with; how many atoms do you think are in 12 grams of graphite or carbon????????
How many items make up a dozen????? How many items make up a half dozen???? How many items are in two dozen??

21. The Mole
In the previous section we used atomic mass units for mass, but these are extremely small units
In a laboratory, the gram is the preferred and more convenient unit for mass
Remember our sample of carbon?
It weighs gram
But how many atoms are in a sample of carbon that weighs grams?

22. The Mole Lets look at the periodic table
What is the atomic mass of carbon?
That’s right, 12.01
A sample of carbon with a mass of has x1023 atoms!
The number of atoms present in grams of carbon is called the mole

23. Number of Atoms Present Average Atomic Mass in grams
How many
atoms does
1.008 grams of
hydrogen contain?
Element
Number of Atoms Present
Average Atomic Mass in grams
Hydrogen
6.022 x1023
1.008
Helium
4.00
Carbon
12.01
Nitrogen
14.01
Oxygen
16.00
Aluminum
26.98
Sodium
22.99
How many
atoms does
14.01 grams of
nitrogen contain?
The point is,
a sample
Of any element
that weighs
A number of
grams equal
To the average
atomic mass of
that element
contains
6.022 x1023 atoms!
How many
atoms does
4.00 grams of
helium contain?
How many
atoms does
12.01 grams of
carbon contain?
6.022 x1023
6.022 x1023
6.022 x1023
6.022 x1023

24. What is a Mole?
The _____ of a substance that contains __________ particles of a substance
It is also the number equal to the amount of carbon atoms in _____ grams of carbon
amount
Answer Bank
12.01
Atoms 24
Amount
6.022 x 1023(2)
6.022 x 1023
12.01

25. The Mole
As it turns out, one mole of anything contains x1023 units of that substance
Just as a dozen eggs is 12 eggs, a mole of eggs is x1023 eggs
The mole is an incredibly large number to imagine - 602,000,000,000,000,000,000,000!!!!!!!!!!!!!!!!!
We use scientific notation to simply this number
We call this unbelievably large number Avogadro’s number

26. The Mole If I have a dozen eggs how many eggs do I have?
If I have 2 dozen eggs, how many eggs do I have?
If I have a mole of eggs, how many eggs do I have?
If I have a 2 mole of eggs, how many eggs do I have? 2 (6.022 x 1023)

27. What is Avogadro’s Number?
The amount of _____ in 1 mole of a substance which is ________
Just as two dozen is (2) x (12), or ____eggs, a mole of atoms is equal to (2) x (6.022 x 1023 ) atoms
atoms
Answer Bank
12.01
Atoms 24
Amount
6.022 x 1023(2)
6.022 x 1023 24

28. The Mole
Consider the following sample of hydrogen atoms below (symbolized by red dots) which contains one mole (6.022 x 1023) of hydrogen atoms
Now consider another sample in which the number of hydrogen atoms is unknown
Sample A = grams
Sample B = grams

29. The Mole We know sample A has 6.022 x1023 hydrogen atoms
But how many atoms are in sample B?
We know the mass is grams
Sample A = grams
Sample B = grams

30. The Mole Let’s consider what we know
We know that 1 mol of hydrogen atoms has a mass of grams
Sample B has a mass of grams which is exactly half the mass of a mole of hydrogen atoms
Sample A = grams
Sample B = grams

31. The Mole Let’s consider what we know
We know that 1 mol of hydrogen atoms has a mass of grams
Sample B has a mass of grams which is exactly half the mass of a mole of hydrogen atoms
Sample A = grams
Sample B = grams

32. Our conversion factor is:
The Mole
Our conversion factor is:
1mol hydrogen
1.008 grams
Let’s do the math!
0.500 grams of hydrogen
1 mol hydrogen
We know we
have grams
of hydrogen
= mol
of hydrogen
in sample B
1.008 grams of hydrogen
Sample A = grams
Sample B = grams

33. Our conversion factor is:
The Mole
Our conversion factor is:
6.022 x1023
1 mol
Now that we have moles, we can compute the number of atoms by using our conversion factor
0.496 mol of hydrogen
6.022 x1023 hydrogen atoms
We solved for moles
In the last example
= 2.99 x1023
hydrogen atoms
in sample B
1 mol of hydrogen
Sample A = grams
Contains x1023 Atoms
Sample B = grams
Contains ???? Atoms

34. Practice: Your chicken laid 562 eggs. How many dozen eggs do you have?

35. Practice: How many moles are in a 42 gram sample of aluminum?
42 grams Al
1 mol aluminum
= 1.56 mol
of Aluminum
26.98 grams Al

36. Practice: How many atoms are in 1.56 mol of aluminum? = 9.39 x1023
moles
number of atoms
1.56 mol Al
6.022 x1023 Al atoms
= 9.39 x1023
Aluminum Atoms
1 mol Al

37. Practice: Calculate the mass of 1.56 mol of Aluminum: = 42 grams
moles
grams
1.56 mol Al
26.98 grams Al
= 42 grams
Aluminum
1 mol Al

38. Practice: How many atoms are in a 18 gram sample of carbon?
moles
number of atoms
18 grams C
1 mol C
6.022 x1023 C atoms
= 9.07 x1023
Carbon Atoms
1 mol C
12.01 grams C

39. Summarize: If I have a _____of something I have_______ particles
Avogadro number is ___________
A mole of carbon atoms weighs(mass) ______grams and contains ______ atoms
2 moles of carbons atoms weighs _____ grams
Review: An ______ is atom with a different amount of neutron than protons

40. Topic: Molar Mass/Molecular Weight
Unit: The Mole and Atomic Mass
Topic: Molar Mass/Molecular Weight
Objectives: Day 3 of 3
To learn how to calculate Molar Mass
To learn how to convert between moles and grams
To learn how to calculate % composition

41. Quickwrite Answer one of the questions below 1-2 sentences:
Let’s say you want to find the weight of your dog, which is too big to stand on your bathroom scale; how could you find his weight???
Together, you and your dog weigh 100 kilograms, you know that you weigh 75 kilograms, what percent by weight does your dog weigh????

42. Molar Mass/Molecular Weight
A chemical compound such as methane (CH4) is a collection of atoms
Methane contains 1 carbon atom and 4 hydrogen atoms
But how do we calculate the mass of one mol of methane?
In other words, what is the mass of x1023 C methane molecules?

43. Molar Mass/Molecular Weight
Because each methane molecule (CH4) contains one carbon atom and 4 hydrogen atoms, 1 mol (CH4) molecules consists of 1 mol carbon atoms and 4 mol of hydrogen atoms
So the mass of 1 mol of (CH4) is equal to:
Mass of 1 mol of carbon (C) = 1 x 12.01g = g
Mass of 4 mol of hydrogen (H) = 4 x = 4.032g
_______
Mass of 1 mol of (CH4) = g

44. 1 CH4 molecule 1 C atom 4 hydrogen atoms 10 CH4 molecule
10 C atoms hydrogen atoms
1 mol of C atoms
(6.022 x1023 C atoms)
1 mol of CH4 molecules
(6.022 x1023 CH4 molecules)
4 mol of H atoms
4 (6.022 x1023 H atoms)

45. What is molar mass or molecular weight?
It is the mass in grams of one _____
of a substance or compound
It is found by _______ the atomic
________that make up a compound
or molecule
Ex: methane
Mass of 1 mol of carbon (C) = 1 x 12.01g = g
Mass of 4 mol of hydrogen (H) = 4 x = 4.032g
mole
Answer Bank
Total
Percent
Element
adding
mole
masses
adding
masses
_______
Mass of 1 mol of (CH4) = g

46. Practice: Calculate the molar mass of sulfur dioxide:
Mass of 1 mol of sulfur (S) = 1 x g = g
Mass of 2 mol of oxygen (O) = 2 x g = g
_______
Mass of 1 mol of (SO2) = g

47. Mass of 1 mol of (CaCO3): = 100.09 g
Practice:
A sample of calcium carbonate (chalk) contains 4.86 mol. What is the mass in grams of this sample:
First calculate the molar mass of CaCO3:
Mass of 1 mol of Calcium (Ca)=1 x g = g
Mass of 1 mol of Carbon (C) =1x g = g
Mass of 3 mol of Oxygen (O) =3 x g = g
_______
Mass of 1 mol of (CaCO3): = g
4.86 mol CaCO3
= 486 grams CaCO3
grams CaCO3
1 mol CaCO3

48. Practice:
A sample of water weighs grams. How many water molecules are in a sample of water that weighs grams?
gms H2O
1 mol of H2O
6.022 x1023 H2O molecules
=6.87 x 1023
molecules
1 mol H2O
gms H2O

49. Percent Composition
Chemists often need to know a chemical’s composition in terms of the masses of it’s elements
We can obtain this information from the formula of the compound by comparing the mass of each element present in 1 mol of the compound to the total mass of 1 mol of the compound

50. Mass of the element present in 1 mol of compound
Percent Composition
The mass fraction for each element is calculated as follows:
Mass
for a given =
element
Mass of the element present in 1 mol of compound
Mass of 1 mol of compound

51. Mass of 1 mol of C2H6O ethanol = 46.07 g = molar mass
For example, lets consider ethanol (C2H6O):
We calculate the mass of each element present and the molar mass of ethanol as follows:
Mass of C = 2 mol C
= g C x100 = % C
46.07 g C2H6O
12.01 grams C
1 mol C
Mass of H = 6 mol H
= g H x100 = 13.13% H
46.07 g C2H6O
1.008 grams H
1 mol H
Mass of O = 1 mol O
= g O x 100 = 34.73% O
46.07 g C2H6O
16.00 grams O
1 mol O
Mass of 1 mol of C2H6O ethanol = g = molar mass

52. The mass percent of carbon in ethanol can be computed by comparing the mass of carbon in 1 mol of ethanol with the total mass of 1 mol of ethanol and multiplying the result by 100%
Mass % of C =
24.02 g x 100% = 52.14%
= g
Mass of C in 1 mol C2H6O
Mass of 1 mol C2H6O
6.048 g x 100% = 13.13%
= g
Mass of H in 1 mol C2H6O
Mass of 1 mol C2H6O
Mass % of H =
Mass % of O =
16.00 g x 100% = 34.73%
= g
Mass of O in 1 mol C2H6O
Mass of 1 mol C2H6O

53. Percent Composition
To review, by weight, ethanol contains 52.14% carbon, 13.13% hydrogen, and 34.73% Oxygen
Or, 52.14% % % = 100%

54. What is Mass Percent?
The ________by mass of an ________ in a compound or molecule
Mass % is calculated by comparing the mass of a single element to the _____ mass (molar mass) of the compound
percent
Answer Bank
Total
Percent
Element
adding
mole
masses
element
total

55. Practice:
Find the weight percent of oxygen in water H2O:

56. Practice: First calculate the molar mass of H2O:
A sample of water weighs grams. How many moles of water are in grams of water?
Mass of 2 mol of hydrogen (H)= 2 x g = g
Mass of 1 mol of oxygen (O) = 1 x g = g
_______
Mass of 1 mol of (H2O): = g
grams H2O
= 1.14 mol H2O
1 mol of H2O
grams H2O

57. Summarize: _____ _____is the mass in grams of one mole of a substance
To calculate Molar mass, you would add up the ____ ______for each element that make up a molecule
The percent by mass of an element in a compound is called it’s ______ ______
Calculate the percentage of nitrogen in nitrogen dioxide NO2