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PA
Problem Set 3
Due Tuesday Oct 15th
The Structure and History of the Atom
Early Theories of Matter: Remember to USE YOUR TEXTBOOK for more information
Conceptual questions
1) What are the major components of Democritus’s Atomic Philosophy?
2) What is wrong with Democritus’s ideas?
3) What are the 5 major components of Dalton’s Atomic Theory?
4) What is wrong with Dalton’s Atomic Theory?
5) What is correct in Dalton’s Atomic Theory?
Practice Questions
6) True False Questions – determine if the following statements are true or false
according to Democritus’s ideas about atoms.
A. Atoms are divisible.
B. Atoms are hard dense spheres
C. Changes in matter are due to the changes in atoms.
7) True False Questions – determine if the following statements are true or false
according Dalton’s Atomic Theory
A. All matter is made of small particles called atoms.
B. Atoms are divisible.
C. Atoms of the same element are identical
D. Atoms can be separated, combined or rearranged
Extension Questions
8) What is a Scanning Tunneling Microscope? Briefly describe what it does and why it
is an important tool for scientists.
9) Why do you think Dalton’s Atomic theory is still taught in school, even though it is
over 200 years old?
Sub-Atomic Particles and the Nuclear Atom: text book
Conceptual Questions
10) The cathode ray tube was used to discover the electron. Re-Draw the diagram from
your notes and include what the ray looks like when the + end of a magnet is brought
near the ray.
11) What conclusion did Thomson draw from his observations?
12) Rutherford used radioactive material to fire positively charged particles at thin sheets
of metal.
A. What is the name of those particles?
B. What is the composition of those particles?
13) Create a diagram of Rutherford’s Gold Foil Experiment. Be sure to include the
following details: the alpha particles, the radioactive polonium, the zinc sulfide lining,
the gold foil, and these three locations of hits: the most hits, some hits, and only a
few hits.
14) What were Rutherford’s two observations from his famous experiment?
15) What were the two conclusions that correspond to the Rutherford’s two observations?
Be sure to connect each conclusion with the appropriate observation.
Practice Questions
16) Who determined that electrons exist?
17) Who determined the mass of an electron?
18) What is the mass of an electron? A proton? A neutron?
19) Who determined that the nucleus of an atom exists?
20) Who determined the charge of nucleus?
21) What is the charge of the nucleus?
22) Who determined that neutrons exist?
Extension Questions
23) Draw three historical pictures of an atom if we could take a picture of it…be as
detailed as possible
A. Dalton’s Perspective
B. Thomson and Millikan’s Perspective
C. Rutherford and Chadwick’s Perspective
24) Why do you think we are starting with the atom in chemistry class?
25) Propose a reason for a neutron to be ever so slightly more massive than a proton.
26) Diagram one of the experiments on the atom on one page of blank paper. Make it
colorful, big, label it… these will be posted in the room as we progress through our
study of the atom.
How Atoms Differ: USE YOUR TEXTBOOK!!!
Conceptual Questions
27) Define the following terms
A. Atomic number
c. Average Atomic Mass
B. Isotope
d. Percent Abundance
28) How are isotopes of the same element alike?
29) How are isotopes of the same element different?
30) What sub-atomic particle(s) identify/(ies) an element?
31) What sub-atomic particle(s) determine(s) the isotope of an element?
32) Use the data below to calculate the average atomic weight for compound X. Then use
your periodic table to identify element X.
Isotope 1 = 90. 00 %, 39 a.m.u.
Isotope 2 = 9.000 %, 40 a.m.u.
Isotope 3 = 1.000 %, 41 a.m.u.
33) One of the stable isotopes of tins is tin-119. The atomic number of tin is 50. How
many protons, neutrons and electrons are in one atom of this isotope of tin?
34) What is the atomic mass of an isotope of potassium that has 21 neutrons?
Practice Questions
35) Fill in this table for each atom or ion. You may write on the Problem Set… rather
than re-draw the table in your responses.
Isotope
Symbol
# p+ #e - #no
Atomic
Mass
Charge
Name
Number
Number
Tin - 118
118
50
Sn
68
19
19
18
F -1
0
40
10
-1
7
-3
9
10
tellurium – 128
52
128
Extension Questions
36) List the steps needed to calculate the average atomic mass if you are given the
relative abundance and mass of each isotope known to exist.
37) Nitrogen has two naturally occurring isotopes: nitrogen-14 and nitrogen-15. The
average atomic mass of nitrogen is 14.0007 amu. Which isotope is more abundant?
Explain.
Answers to Practice Problems –
Remember that learning from our mistakes is how science (and our understanding of the
world around us) has improved over time!
6) a. false b. true c. false
7) a. true b. false c. true d. true
16) J. J. Thomson
17) Robert Millikan
18) e- = 9.1 x 10-28 grams
p+ =1.67 x 10-24grams
no = 1.675 x 10-24 grams
19) Ernest Rutherford
20) Ernest Rutherford
21) Positive
22) Chadwick
35)
Isotope
Name
tin - 118
Symbol
118
Sn
40
K +1
19
# p+
#e -
#no
50
50
19
Mass
Number
118
Charge
68
Atomic
Number
50
18
21
19
40
+1
9
10
10
9
19
-1
7
10
7
7
14
-3
52
52
76
52
128
0
0
50
Potassium-40
Fluorine -19
19
F -1
9
Nitrogen -14
14
7
N
128
tellurium - 128
52
-3
Te