400 Chemistry Problems
Atomic Structure
1. What is the smallest particle of an element?
2. What did Democritus believe about atoms? Were all of his ideas correct
(explain)?
3. Who disagreed with Democritus? What did he believe? Was he correct
(explain)?
4. What did John Dalton believe about atoms?
5. Which of Dalton’s ideas are known to be true today? Which ones are not?
6. What did J.J. Thomson believe about atoms? Were all of his ideas correct
(explain)?
7. Describe Rutherford’s gold foil experiment. What did it teach us about atoms?
8. What were Bohr’s ideas about atoms? Were all of his ideas correct (explain)?
9. What is the basic idea behind the quantum mechanical model used for atoms
today?
10. Name the three particles that make up the atom. For each one, give its relative
charge and relative mass.
11. How do you determine how many protons, neutrons, and electrons are in an atom
of an element?
12. How many protons does potassium have?
13. How many protons would the element directly to the right of strontium have?
Explain.
14. Fill in the table below for atoms of the following elements:
Name
Symbol Atomic Atomic Mass
Number Number Number
Number Mass
Number of
of
of
Protons Neutrons Electrons
Carbon
Hydrogen
Manganese
Iron
Cobalt
Chlorine
Silver
Xenon
Chromium
Sodium
15. Which element has no neutrons?
16. How many electrons does boron have?
17. What is nitrogen’s atomic number?
18. Which element has an atomic number of 35?
19. What is the chemical symbol of the element with an atomic number of 77?
20. Which element has 78 protons?
21. Which element has 12 electrons?
22. How many protons does the element in #21 have?
23. What is the name of the element with 89 electrons?
24. What is the symbol of the element with 34 protons?
25. Which element has an atomic mass of 63.546?
26. What is the mass number for the element in #25?
27. Which element has a mass number of 127?
28. How many protons, neutrons, and electrons does the element in #27 have?
29. What is an ion?
30. What makes an ion have a positive charge?
31. What makes an ion have a negative charge?
32. What is the difference between an anion and a cation?
33. How are anions formed? How are cations formed?
34. What is an isotope?
35. Why is the mass of an isotope different than that of a normal atom?
36. Fill in the table below for atoms, ions, and isotopes of various elements.
Symbol
What is
Atomic
Atomic
Mass
Number Number Number
it?
number
mass
number
of
of
of
(neutral
protons
neutrons electrons
atom,
ion, or
isotope)
Ar
Neutral
atom
K+1
Ion
-2
S
Ion
234
U
Isotope
N/A
14
C
N/A
Ne
106
Ag
N/A
-3
P
Cl-1
Sr+2
Al+3
Mg
104
Ru
N/A
37. Write down the atomic masses for N, S, Cl, and Zn.
38. If the atomic mass is due to the number of protons and neutrons (which we know
exist only as whole numbers) and the numbers you listed in #37 are not whole
numbers, does this suggest a problem or that something else is going on that we
don’t yet understand?
39. Consider the following problem. A teacher is calculating grades. She has told the
students that tests will count for 40% of the grade, quizzes for 20%, homework
for 20%, and labs for 20%. Jamel has a test average of 87, a quiz average of 82, a
homework average of 90, and a lab average of 79. How will the teacher calculate
his grade? See if you can calculate Jamel’s grade.
40. How might the problem of atomic masses be related to the way the teacher
calculates grades?
Note: On the average atomic mass problems that follow, DO NOT round! Show
work!
41. Find the average atomic mass of carbon if it consists of 2 isotopes (Carbon-12
with an atomic mass of 12 amu and 98.89% abundance and Carbon-13 with an
atomic mass of 13.0034 amu and 1.11% abundance.
42. Find the average atomic mass of iodine if it consists of 80% iodine-127, 17%
iodine-126, and 3% iodine-128.
43. Calculate the average atomic mass of gold if half (i.e., 50%) of the gold found in
nature has a mass of 197 amu and half has a mass of 198 amu.
44. Calculate the average atomic mass of iron if 15% of the iron found in nature is
55
Fe and 85% of the iron found in nature is 56Fe.
45. Find the average atomic mass of hydrogen given the following isotopic masses
and natural percents of abundance: 99% 1H, 0.8% 2H, and 0.2% 3H.
46. Calculate the average atomic mass of nitrogen given the following isotopic
masses and natural percents of abundance: nitrogen-14 (95%), nitrogen-15 (3%),
and nitrogen-16 (2%).
47. Rubidium has two common isotopes, 85Rb and 87Rb. If the abundance of 85Rb is
72.2%, and the abundance of 87Rb is 27.8%, what is the average atomic mass of
rubidium?
48. Uranium has three common isotopes. If the abundance of 234U is 0.01%, the
abundance of 235U is 0.71%, and the abundance of 238U is 99.28%, what is the
average atomic mass of uranium?
49. Titanium has five common isotopes with the percents of abundance listed as
follows: Titanium-46 (8.0%), Titanium-47 (7.8%), Titanium-48 (73.4%),
Titanium-49 (5.5%), and Titanium-50 (5.3%). What is the average atomic mass
of titanium?
50. Oxygen has 3 isotopes: Oxygen-16 with a percent abundance of 99.759%,
Oxygen-17 with a percent abundance of 0.037%, and Oxygen-18 with a percent
abundance of 0.204%. Calculate its average atomic mass.
51. Find the average atomic mass of sulfur if 95.00% is 32S, 0.76% is 33S, 4.22% is
34
S, and 0.014% is 36S.
52. Given the following isotopes and average atomic masses, find the natural percent
abundance of each isotope:
a. Hydrogen-1 and hydrogen-2, average mass = 1.0079 amu
b. Helium-3 and helium-4, average mass = 4.0026 amu
c. Carbon-12 and carbon-13, average mass = 12.011 amu
d. Nitrogen-14 and nitrogen-15, average mass = 14.007 amu
e. Chlorine-35 and chlorine-37, average mass = 35.453 amu
For additional practice:
Relevant sections in book are 2.1-2.5
Additional practice problems can be found on p. 76 (43-50)