Download Beanium Lab Make Up

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Beanium Lab Makeup Worksheet: Atomic Structure
Average Atomic Mass Problems
Average atomic mass: the weighted average of the masses of all the isotopes of that element. A weighted average reflects both the
mass and the abundance of the isotopes as they occur in nature.
Isotope
Atomic mass
abundance (%)
H-1
1.0078amu
99.985%
H-2
2.0141amu
0.015%
H-3
3.0160amu
negligible
The average atomic mass of hydrogen is 1.0079amu. Multiply each atomic mass by the percent abundance and add them up.
(1.0078amu)(.99985) + (2.0141amu)(0.00015) = 1.0079amu
Fill in the missing information. Calculate the average atomic mass of each element (show work).
1. Carbon
Nuclear
Symbol-Mass # % Abundance Mass of Atom
# protons
# electrons
# neutrons
Symbol
12
C-12
98.93%
12.00amu
C
6
C-13
1.07%
13.00amu
negligible
14.00amu
6
8
Average Atomic Mass of Carbon=____________
2. Potassium
Symbol-Mass #
% Abundance
Mass of Atom
K-39
93.26%
38.96amu
# protons
# electrons
# neutrons
Nuclear
Symbol
39
K
19
K-40
0.01%
39.96amu
6.73%
40.96amu
Average Atomic Mass of Carbon=____________
19
22
3. Nitrogen
Symbol-Mass #
% Abundance
Mass of Atom
N-14
99.632%
14.00amu
0.0368%
15.00amu
# protons
# electrons
7
# neutrons
Nuclear
Symbol
8
Average Atomic Mass of Carbon=____________
4. Chlorine
Symbol-Mass #
% Abundance
Mass of Atom
Cl-35
75.78%
34.97amu
24.22%
36.97amu
# protons
# electrons
17
# neutrons
Nuclear
Symbol
20
Average Atomic Mass of Carbon=____________
5. Oxygen
Symbol-Mass #
% Abundance
Mass of Atom
O-16
99.757%
15.99amu
O-17
0.038%
16.99amu
O-18
0.205%
18.00amu
Average Atomic Mass of Carbon=____________
# protons
# electrons
# neutrons
Nuclear
Symbol
6. Silver
Symbol-Mass #
% Abundance
Mass of Atom
Ag-107
51.839%
106.91amu
48.161%
108.90amu
# protons
# electrons
47
# neutrons
Nuclear
Symbol
62
Average Atomic Mass of Carbon=____________
7. Copper
Symbol-Mass #
% Abundance
Mass of Atom
Cu-63
69.17%
62.93amu
Cu-65
30.83%
64.93amu
# protons
# electrons
# neutrons
Nuclear
Symbol
Average Atomic Mass of Carbon=____________
9. Element Z has 2 natural isotopes. One isotope has a of 15.0amu and has a relative abundance of 30%. The
other isotope has a mass of 16.0amu and has a relative abundance of 70%. Estimate the average atomic mass for
this element to one decimal place.
10. Three isotopes of argon occur in nature – Ar-36, Ar-38, Ar-40. Calculate the average atomic mass of argon
to two decimal places, given the following relative atomic masses and abundances of each of the isotopes: Ar36 (35.97amu; 0.337%), Ar-38 (37.96amu; 0.063%), and Ar-40 (39.96amu; 99.600%).
11. Naturally occurring boron is 80.20% boron-11 (atomic mass = 11.01amu) and 19.80% of some other
isotopic form of boron. What must the atomic mass of this second isotope be in order to account for the
10.81amu average atomic mass of boron?