Name
Period 1 2 3 4 5 6 7
Atomic Structure WKST #3
Show all of your work. Round all answers to the hundredths place.
Rules for calculating AVERAGE ATOMIC MASS
1. Convert Percentages into DECIMALS
These percentages are your percent abundance #’s
(Divide by 100)
2. Multiply the percent abundance DECIMALS by its relative atomic mass
3. Add ALL the numbers from STEP 2 together
1. Calculate the average atomic mass of iron if its abundance in nature is 15% iron-55 and 85% iron-56.
2. What is the average atomic mass of silicon if 92.21 % of its atoms have a mass of 27.977 amu,
4.07 % have a mass of 28.976 amu, and 3.09 % have a mass of 29.974 amu?
3. Calculate the average atomic mass for neon if its abundance in nature is 90.5% neon-20,
0.3% neon-21, and 9.2% neon-22.
4. Calculate the average atomic mass of silver if 13 out of 25 atoms are silver-107 and 12 out of 25
atoms are silver-109.
5. Boron has three naturally occurring isotopes: boron-10, boron-11, and boron-12. If the average
atomic mass of boron is 10.811 amu, which isotope is the most abundant? How do you know?
6. Calculate the average atomic mass of chromium.
Isotope
Mass (amu)
Chromium – 50
49.946
Chromium – 52
51.941
Chromium – 53
52.941
Chromium – 54
53.939
Relative Abundance
0.043500
0.83800
0.095000
0.023500
Use your knowledge of subatomic particles to fill in the chart below for each atom or ion.
Name
Symbol
Atomic Mass
#
#
#p+
#n0
#e-
Calcium - 48
_______
___
___
______
______
______
___________
89
39
___
___
______
______
______
___
___
______
______
______
___________
34
16
Y
S
2
___________
_______
10
21
______
______
______
___________
_______
___
___
28
31
______
___________
_______
___
___
31
39
28