Last Name _________________________ First Name __________________ Period ____ Date_______
4.2 Atomic Calculations- Notation and Average Atomic Mass
Nuclear Symbols and Hyphen Notation tell us the Symbol of the Element, the number of protons and the Mass Number (
Protons + Neutrons). You will need your Periodic Table to complete this worksheet.
PART A - Convert the following between Nuclear Symbols and Hyphen Notation.
Nuclear
Symbol
Hyphen
Notation
17
8𝑂
15
7𝑁
41
19𝐾
22
10𝑁 𝑒
36
17𝐶𝑙
O- 17
N- 15
K - 41
Ne-22
Cl - 36
PART B - Find or calculate the number of protons, electrons and neutrons in each of the following neutral atoms:
Symbol
17
22
35
8𝑂
Protons
8
Neutrons
17 – 8 = 9
17𝐶𝑙
K - 41
17
19
35 – 17 = 18
41 – 19 = 22
10𝑁 𝑒
Cl - 36
10
17
22 – 10 = 12
36 – 17 = 19
Calculating Average Atomic Mass from Abundance of Isotopes and their Mass
Please See Examples on the Website
Calculate the Average Atomic Masses as stated below.
1. K has 2 abundant isotopes. They are K – 39 (abundance is 93.12%) and the remainder is K – 41 .
a. Calculate the % that is K -41. (You should know how to do this)
100% - 93.12 % = 6.88%
a. Calculate the Average Atomic Mass using the table given (39.14 amu)
%
0.9312
0.0688
Mass
Subtotal
K-39
39
36.3168
K-41
41
2.8208
Total -> 39.1376
2. The natural abundance of Boron isotopes is : 19.9 % B-10 and 80.1% B – 11 Calculate the atomic mass of boron.
Create a table as shown in the example above. Include units with your numbers. (10.81 amu)
B-10
B-11
%
0.199
0.801
Mass
10
11
Total ->
Subtotal
1.99
8.811
10.801
3. The natural abundance of Gallium isotopes is : 60.11 % Ga-69 and 39.89% Ga – 71. Calculate the atomic mass of
Gallium. . Include units with your numbers. (69.8 amu)
Ga - 69
Ga - 71
%
0.6011
0.3989
Mass
69
71
Total ->
Subtotal
41.4759
28.3219
69.7978
HERE ARE SOME MORE COMPLEX
4.
Mass #
24
25
26
%
0.7899
0.1
0.1101
Total ->
18.9576
2.5
2.8626
24.3202
5.
Mass
27.97693
28.9765
29.97377
%
0.9223
0.0467
0.031
Total ->
25.80312
1.353202
0.929187
28.08551
OPTIONAL QUESTION
EXTRA CREDIT = 2 POINTS ON YOUR UNIT TEST. Complete the calculation of the
Average Atomic Mass for Molybdenum (data shown to the right) in and Excel Spread
sheet. To receive the credit you must:
 Include your name
 Hand in on time (late submissions will not be accepted for any credit)
 Print out the calculation
 Print out the equations/formulas used in excel (To view eq/form CTRL ~)
 Submit a copy by email
Mass
92
94
95
96
97
98
100
%
0.1484
0.0925
0.1592
0.1668
0.0955
0.2413
0.0963
Total ->
13.6528
8.695
15.124
16.0128
9.2635
23.6474
9.63
96.0255
EQUATIONS
Mass
92
94
95
96
97
98
100
%
0.1484
0.0925
0.1592
0.1668
0.0955
0.2413
0.0963
Total ->
=D3*E3
=D4*E4
=D5*E5
=D6*E6
=D7*E7
=D8*E8
=D9*E9
=SUM(F3:F9)
6. CONCEPTUAL QUESTION - Silver has an atomic mass of 107.868 amu. Does any atom of any isotope of silver have a
mass of 107.868 amu? Explain why.
The atomic mass represents the average of all abundant masses present. It is possible but unlikely that it will be equal to
the mass of any isotope, just like it is unlikely that a class average will be the grade for any one student.
7. HERE IS A MORE CHALLENGING QUESTION REQUIRING SOME ALGEBRA
The atomic mass of Cu is 63.540 amu. It is composed of two isotopes, Cu-63 and Cu-65, with atomic masses of 62.930
and 64.928. What is the % abundance of these isotopes?
HINT 1 : IF you calculate one, you will know the other.
HINT 2: What is the relation between the two % abundances?
HINT 3: Use the following Equation: Atomic Mass = (% Cu-63 x mass Cu-63) + (% Cu-65 x mass Cu-65)
Since the total % Abundance = 100% an equation between the two can be written as
X + Y = 100 , assign X = % Abundance of Cu-63 and Y = % Abundance of Cu-65
So Y = 100 – X
63.540 = (63 X) + (65 Y) but this has two unknowns so it cant be solved. Yes, it can if Y = 100 – X is used as
follows:
63.540 = (63 X) + (65(1.00-X)) now solve for X
63.540 = 63X + 65-65X
Now collect the X terms and constants:
Now collect the constants: -1.46 = -2X
63.540 = 65-2X
Divide both sides by -2 which gives the value of X
𝑿=
The other percent 100 – 73 = 27%
Solution: Cu – 65 is 27% & Cu – 63 is 73%
−𝟏. 𝟒𝟔
=. 𝟕𝟑
−𝟐