topic: iosotopes and avg. atomic mass
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Topic: Iosotopes and Avg. Atomic Mass. Do Now:. Dalton 1766. Atoms (tiny) Atoms of same element are identical * Indestructible * Combine in whole # ratio (H 2 O) In chem rxn . are combined, separated, rearranged *turned out to not be entirely be true. - PowerPoint PPT PresentationTRANSCRIPT
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Topic: Iosotopes and Avg. Atomic Mass
Do Now:
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Dalton1766
Remember #2…well Dalton was correct…
1) Atoms (tiny)2) Atoms of same element
are identical *3) Indestructible *4) Combine in whole # ratio
(H2O)5) In chem rxn. are
combined, separated, rearranged
*turned out to not be entirely be true
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These three hydrogens are found in nature
All H’s have 1 proton H-1: mass # = 1
1-1 = 0 neutrons H-2: mass # = 2
2-1 = 1neutron H-3: mass # = 3
3-1 = 2 neutrons
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Isotopes
atoms of same element with different # neutrons (mass # is
different) # protons stays same! (atomic # is
same)
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Consider U-234, U-235, & U-238
What’s the atomic number of U? How many protons in U? How many neutrons in U-234? How many neutrons in U-235? How many neutrons in U-238? How many electrons in U?
92
92234 – 92 = 142
235 – 92 = 143
238 – 92 = 146
92
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Average Atomic Mass
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Average Atomic Mass
The atomic masses reported in the periodic table represent the weighted average of the masses of the naturally occurring isotopes of that element
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Unit for Avg. Atomic Mass =
Amu (or regents says just u) – atomic mass unit Define as 1/12 the mass of a Carbon-12
atom
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Avg. Atomic Mass of Chlorine (Cl has 2 isotopes)
24.230%Cl-37
75.770%Cl-35
% Abundance
Mass(percent) + mass(percent) +…= avg. atomic mass
35(.75770) + 37(.24230) = 35.453 amu
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NOW YOU TRYAvg. Atomic Mass of Si
92.21% of Si has a mass of 27.97693 amu
4.70% of Si has a mass of 28.97649 amu
3.09% of Si has a mass of 29.97376 amu
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Avg. Atomic Mass of Si
0.9221 X 27.97693 25.7975 amu
0.0470 X 28.97649 1.3619 amu
+ 0.0309 X 29.97376 0.9262 amu
28.0856 amu