Average Atomic Mass. carbon atom (12 amu) Measuring Atomic Mass Unit is the Atomic Mass Unit (amu)...
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Transcript of Average Atomic Mass. carbon atom (12 amu) Measuring Atomic Mass Unit is the Atomic Mass Unit (amu)...
![Page 1: Average Atomic Mass. carbon atom (12 amu) Measuring Atomic Mass Unit is the Atomic Mass Unit (amu) One twelfth the mass of a carbon-12 atom. Each isotope.](https://reader035.fdocuments.us/reader035/viewer/2022081506/56649e185503460f94b03f12/html5/thumbnails/1.jpg)
Average Atomic Mass
![Page 2: Average Atomic Mass. carbon atom (12 amu) Measuring Atomic Mass Unit is the Atomic Mass Unit (amu) One twelfth the mass of a carbon-12 atom. Each isotope.](https://reader035.fdocuments.us/reader035/viewer/2022081506/56649e185503460f94b03f12/html5/thumbnails/2.jpg)
Isotopes• Atoms of the same element with
different numbers of neutrons.
• Isotopes have the same number of protons, so the atomic number is the same. The atomic mass is different because the neutrons are different.
• Different isotopes of the same element are identified by their atomic mass. (IE: Carbon-12, Carbon-14)
![Page 3: Average Atomic Mass. carbon atom (12 amu) Measuring Atomic Mass Unit is the Atomic Mass Unit (amu) One twelfth the mass of a carbon-12 atom. Each isotope.](https://reader035.fdocuments.us/reader035/viewer/2022081506/56649e185503460f94b03f12/html5/thumbnails/3.jpg)
Isotopes
• Because of the existence of isotopes, the mass of a collection of atoms has an average value.
• Average mass = ATOMIC WEIGHT
![Page 4: Average Atomic Mass. carbon atom (12 amu) Measuring Atomic Mass Unit is the Atomic Mass Unit (amu) One twelfth the mass of a carbon-12 atom. Each isotope.](https://reader035.fdocuments.us/reader035/viewer/2022081506/56649e185503460f94b03f12/html5/thumbnails/4.jpg)
Example
• Boron is 20% B-10 and 80% B-11. • That is, B-11 is 80 percent abundant on
earth.
• For boron atomic weight= 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu
![Page 5: Average Atomic Mass. carbon atom (12 amu) Measuring Atomic Mass Unit is the Atomic Mass Unit (amu) One twelfth the mass of a carbon-12 atom. Each isotope.](https://reader035.fdocuments.us/reader035/viewer/2022081506/56649e185503460f94b03f12/html5/thumbnails/5.jpg)
Average Atomic Mass
• weighted average of all isotopes• on the Periodic Table• round to 2 decimal places
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Avg.AtomicMass
= (mass)(%) + (mass)(%)
100
![Page 6: Average Atomic Mass. carbon atom (12 amu) Measuring Atomic Mass Unit is the Atomic Mass Unit (amu) One twelfth the mass of a carbon-12 atom. Each isotope.](https://reader035.fdocuments.us/reader035/viewer/2022081506/56649e185503460f94b03f12/html5/thumbnails/6.jpg)
Average Atomic Mass
• EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O.
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Avg.AtomicMass
= (16)(99.76) + (17)(0.04) + (18)(0.20)
100= 16.00
amu
![Page 7: Average Atomic Mass. carbon atom (12 amu) Measuring Atomic Mass Unit is the Atomic Mass Unit (amu) One twelfth the mass of a carbon-12 atom. Each isotope.](https://reader035.fdocuments.us/reader035/viewer/2022081506/56649e185503460f94b03f12/html5/thumbnails/7.jpg)
Average Atomic Mass
• EX: Find chlorine’s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37.
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Avg.AtomicMass
= (35)(8) + (37)(2)
100= 35.40 amu
![Page 8: Average Atomic Mass. carbon atom (12 amu) Measuring Atomic Mass Unit is the Atomic Mass Unit (amu) One twelfth the mass of a carbon-12 atom. Each isotope.](https://reader035.fdocuments.us/reader035/viewer/2022081506/56649e185503460f94b03f12/html5/thumbnails/8.jpg)
100
90
80
70
60
50
40
30
20
10
034 35 36 37
Ab
un
dan
ce
Mass
Mass spectrum of chlorine. Elemental chlorine (Cl2) contains only two isotopes: 34.97 amu (75.53%) and 36.97 (24.47%)
AAM = (34.97 amu)(0.7553) + (36.97 amu)(0.2447)
AAM = (26.412841 amu) + (9.046559 amu)
AAM = 35.4594 amu
Cl-35
Cl-37
Cl35.4594
17
![Page 9: Average Atomic Mass. carbon atom (12 amu) Measuring Atomic Mass Unit is the Atomic Mass Unit (amu) One twelfth the mass of a carbon-12 atom. Each isotope.](https://reader035.fdocuments.us/reader035/viewer/2022081506/56649e185503460f94b03f12/html5/thumbnails/9.jpg)
Mass Spectrum for Mercury
196 197 198 199 200 201 202 203 204
Mass numberMass number
Rel
ativ
e n
umb
er o
f at
oms
Rel
ativ
e n
umb
er o
f at
oms
30
25
20
15
10
5
196 199 201 204
198 200 202
Mass spectrum of mercury vaporMass spectrum of mercury vapor
The percent natural abundances The percent natural abundances for mercury isotopes are:for mercury isotopes are:
Hg-196 0.146%Hg-196 0.146% Hg-198 10.02%Hg-198 10.02% Hg-199 16.84%Hg-199 16.84% Hg-200 23.13%Hg-200 23.13% Hg-201 13.22%Hg-201 13.22% Hg-202 29.80%Hg-202 29.80% Hg-204 6.85%Hg-204 6.85%
(The photographic record has been converted to a scale of relative number of atoms)
![Page 10: Average Atomic Mass. carbon atom (12 amu) Measuring Atomic Mass Unit is the Atomic Mass Unit (amu) One twelfth the mass of a carbon-12 atom. Each isotope.](https://reader035.fdocuments.us/reader035/viewer/2022081506/56649e185503460f94b03f12/html5/thumbnails/10.jpg)
The percent natural abundances The percent natural abundances for mercury isotopes are:for mercury isotopes are:
Hg-196 0.146%Hg-196 0.146% Hg-198 10.02%Hg-198 10.02% Hg-199 16.84%Hg-199 16.84% Hg-200 23.13%Hg-200 23.13% Hg-201 13.22%Hg-201 13.22% Hg-202 29.80%Hg-202 29.80% Hg-204 6.85%Hg-204 6.85%
(0.00146)(196) + (0.1002)(198) + (0.1684)(199) + (0.2313)(200) + (0.1322)(201) + (0.2980)(202) + (0.0685)(204) = x
0.28616 + 19.8396 + 33.5116 + 46.2600 + 26.5722 + 60.1960 + 13.974 = x
x = 200.63956 amu
Hg200.59
80
(% "A")(mass "A") + (% "B")(mass "B") + (% "C")(mass "C") + (% "D")(mass "D") + (% "E")(mass "E") + (% F)(mass F) + (% G)(mass G) = AAM
ABCDEFG
![Page 11: Average Atomic Mass. carbon atom (12 amu) Measuring Atomic Mass Unit is the Atomic Mass Unit (amu) One twelfth the mass of a carbon-12 atom. Each isotope.](https://reader035.fdocuments.us/reader035/viewer/2022081506/56649e185503460f94b03f12/html5/thumbnails/11.jpg)
Mass spectrums reflect the abundance of naturally occurring isotopes.
Hydrogen
Carbon
Nitrogen
Oxygen
Sulfur
Chlorine
Bromine
1H = 99.985% 2H = 0.015%
12C = 98.90% 13C = 1.10%
14N = 99.63% 15N = 0.37%
16O = 99.762% 17O = 0.038% 18O = 0.200%
32S = 95.02% 33S = 0.75%
34S = 4.21% 36S = 0.02%
35Cl = 75.77% 37Cl = 24.23%
79Br = 50.69% 81Br = 49.31%
Natural Abundance of Common Elements
![Page 12: Average Atomic Mass. carbon atom (12 amu) Measuring Atomic Mass Unit is the Atomic Mass Unit (amu) One twelfth the mass of a carbon-12 atom. Each isotope.](https://reader035.fdocuments.us/reader035/viewer/2022081506/56649e185503460f94b03f12/html5/thumbnails/12.jpg)
Atomic Mass
Calculate the atomic mass of copper if copper has two isotopes. 69.1% has a mass of 62.93 amu and the rest has a mass of 64.93 amu.
... )B"" )(massB"" (% )A"" )(massA"" (% (AAM) massatomic Average
Copper for amu 63.548 A.A.M.
amu 20.06337 amu 43.48463 A.A.M.
amu) .93(0.309)(64 amu) .93(0.691)(62 A.A.M.
Cu29
63.548
IsotopeIsotopePercentPercent
AbundanceAbundanceMassMass
Cu-63 69.1 62.93
Cu-65 64.93
43.48463
20.0633730.9
63.548