1. 0:56
0:55
0:54
0:53
0:57
0:58
1:02
1:01
1:00
0:59
0:52
0:51
0:44
0:43
0:42
0:41
0:45
0:46
0:50
0:49
0:48
0:47
1:03
1:04
1:19
1:18
1:17
1:16
1:20
1:21
1:25
1:24
1:23
1:22
1:15
1:14
1:08
1:07
1:06
1:05
1:09
1:10
1:13
1:12
1:11
0:40
0:39
0:09
0:08
0:07
0:06
0:10
0:11
0:15
0:14
0:13
0:12
0:05
0:04
0:00
0:00
0:00
0:00
0:00
0:00
0:03
0:02
0:01
0:00
0:16
0:17
0:32
0:31
0:30
0:29
0:33
0:34
0:38
0:37
0:36
0:35
0:28
0:27
0:21
0:20
0:19
0:18
0:22
0:23
0:26
0:25
0:24
3:00
1:26
2:30
2:29
2:28
2:27
2:31
2:32
2:36
2:35
2:34
2:33
2:26
2:25
2:18
2:17
2:16
2:15
2:19
2:20
2:24
2:23
2:22
2:21
2:37
2:38
2:53
2:52
2:51
2:50
2:54
2:55
2:59
2:58
2:57
2:56
2:49
2:48
2:42
2:41
2:40
2:39
2:43
2:44
2:47
2:46
2:45
1:27
2:14
1:43
1:42
1:41
1:40
1:44
1:45
1:49
1:48
1:47
1:46
1:39
1:38
1:31
1:30
1:29
1:28
1:32
1:33
1:37
1:36
1:35
1:34
2:13
1:50
2:06
2:05
2:04
2:03
2:07
2:08
2:12
2:11
2:10
2:09
1:51
2:02
1:55
1:54
1:53
1:52
2:01
1:56
2:00
1:57
1:59
1:58
Do Now
Three students take a quiz and receive the following grades:
One student scores 95
One student scores 76
One student scores 63
Calculate the average score of the students

2. Atomic masses are calculated in a similar way.
What would the average be if 100 students took the same quiz and received the following grades:
Ninety seven students score 95
One student scores 76
Two students score 63
Atomic masses are calculated in a similar way.

3. Finding a weighted average
Average Atomic Mass
Finding a weighted average

4. Atomic Mass How heavy is an atom of oxygen?
There are different kinds of oxygen atoms.
Average Atomic Mass:
Based on abundance of each element in nature.
Don’t use grams because the numbers would be too small.

5. Atomic Mass Unit is the Atomic Mass Unit (amu)
One twelfth the mass of a carbon-12 atom.
Each isotope has its own atomic mass
we get the average using percent abundance.

6. Calculating Average Atomic Mass
(% as decimal x mass)= # (% as decimal x mass)= # (% as decimal x mass)=+ # #

7. Calculating Average Atomic Mass
You have five rocks, 80% with a mass of 50 g, and 20% with a mass of 60 g. What is the average mass of the rocks?
Average mass = (.80 x 50g)= 40g
(.20 x 60g)=+12g
52g

8. Regents Questions
Calculate the atomic mass of copper if copper has two isotopes. 69.1% has a mass of amu and 30.9% has a mass of amu.

9. Atomic Mass Is not a whole number because it is an average.
This is the reason for decimal numbers on the periodic table.

10. Regents Questions
Magnesium has three isotopes % with a mass of amu, 10.00% with a mass of amu, and the rest with a mass of amu. What is the average atomic mass of magnesium?

11. Bellwork
Carbon has two naturally occurring isotopes % with a mass of 12.00amu and 4.45% with a mass of 14.00amu. What is the average atomic mass of Carbon?