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Problem Set 2a
Chapters 4 and 25
The Structure of the Atom and Nuclear Chemistry
Due Tuesday October 5th
 Your work is to be done on separate sheets of paper.
 All of the papers should be stapled together in the upper left hand corner with this
question sheet at the back of the packet.
 Each of your responses should be numbered the same way as it appears on this packet.
 Do each Conceptual Question. (70% of grade based upon correct answers)
 Try the practice questions until you get the hang of them.(0%) answers on the back
 Try each extension question (30% for trying them)
 Pen or pencil is acceptable. Please no red pens, I’ll / we’ll use those for corrections
 Work together… but don’t copy each other. Copying doesn’t help you learn the material
 Start early… end early… figure out what you already know as soon as you can, and
figure out what you need to know as soon as you can.
You should read chapters 4 and 25 as we progress through this unit.
Chapter 4 The Structure of the Atom
Chapter 25 Nuclear Chemistry
4-1 Early Theories of Matter
4-2 Subatomic Particles
4-3 How Atoms Differ
4-4 Radioactive Decay
25-1 Nuclear Radiation
25-2 Radioactive Decay
25-3 Transmutation
25-4 Fission and Fusion
25-5 Science and Radiation
Section 4-1Early Theories of Matter
Conceptual questions
1) What is still correct with Democritus’s Atomic theory?
2) What is wrong with Democritus’s Atomic Theory?
3) What is still correct with Dalton’s Atomic Theory?
4) What is wrong with Dalton’s Atomic Theory?
Practice Questions
5) True False Questions – determine if the following statements are true or false
according to Democritus’s ideas about atomos.
a.
b.
c.
d.
Atomos are divisible.
Atomos are hard dense spheres
Atomos have varying density – they are heterogeneous.
Changes in matter are due to the changes in atomos.
6) True False Questions – determine if the following statements are true or false
according Dalton’s Atomic Theory
a.
b.
c.
d.
All matter is made of small particles called atoms.
Atoms are divisible.
Atoms of the same element are identical
Atoms can be separated, combined or rearranged
Extension Questions
7) What is a Scanning Tunneling Microscope? Describe what it does and why it is
an important tool for scientists.
8) Why is Dalton’s Atomic theory still taught in school, even though it is over
200 years old?
Section 4-2: Sub-Atomic Particles and the Nuclear Atom
Conceptual Questions
9) The cathode ray tube was used to discover the electron. Re-Draw the diagram
from your notes (or page 92) and include what the ray looks like when the + end
of a magnet is brought near the ray.
10) What conclusion did Thomson draw about the make up of atoms from his
observations of the cathode ray tube?
11) 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?
12) 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.
13) What were Rutherford’s two observations from his famous experiment?
14) What were the two conclusions that correspond to the Rutherford’s two
observations? Connect each conclusion with the appropriate observation.
Practice Questions
15) Who determined that electrons exist?
16) Who determined the mass of an electron?
17) What is the mass of an electron?
18) Who determined that the nucleus of an atom exists?
19) Who determined the charge of nucleus?
20) What is the charge of the nucleus?
21) Who determined that neutrons exist?
22) What is the mass of a proton?
23) What is the mass of a neutron?
Extension Questions
24) 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
25) Propose a reason for a neutron to be ever so slightly more massive than a proton.
Section 4-3 How Atoms Differ
Conceptual Questions
26) Define the following terms
a. Atomic number
b. Isotope
c. Average Atomic Mass
d. Percent Abundance
27) How are isotopes of the same element alike?
28) How are isotopes of the same element different?
29) What sub-atomic particle(s) identify/(ies) an element?
30) What sub-atomic particle(s) determine(s) the isotope of an element?
31) 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.
32) 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?
33) What is the atomic mass of an isotope of potassium that has 21 neutrons?
Practice Questions
34) How many protons in every atom of calcium?
35) How many neutrons in an atom of lithium-7?
36) How many electrons in every atom of magnesium?
37) How many protons, neutrons and electrons are there in an atom of barium-136?
38) 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
118
Tin - 118
68
0
50
Sn
19
19
18
F -1
40
10
-1
7
-3
9
10
52
128
tellurium - 128
Extension Questions
39) 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.
40) 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.
Section 4-4: Radioactive Decay
Conceptual Questions
41) State the law of conservation of mass.
42) Why are atoms unstable?
43) How do unstable atoms gain stability?
44) A radioactive element having atomic number 82 and atomic mass 214 loses a beta
0
particle, –1. What is the resulting particle?
45) What type of decay is the reaction below, and what isotope completes this nuclear
equation?
27
2
4
Al
+
H

13
1
2He + ?
Practice Questions
46) Complete this chart on the three types of radioactive decay
Type
Symbol
Mass (amu)
Alpha
Beta
Gamma
Charge
238
47) If the radioactive atom 92U emits an alpha particle, the atom remaining is
represented by
(A)
238
92U
(B)
236
92Th
(C)
234
92U
(D)
234
234
90Th
(E) 91Pa
48) What term completes this equation?
30
14Si
4
(A)2He
2
1
(B)1H
32
0
+ ?  16S + –1e
0
(C)1H
(D) –1e
214
49) What particle is emitted when lead–214, 82Pb, undergoes natural radioactive
214
decay to bismuth–214, 83Bi?
4
(A)
an alpha particle, 2He
(B)
a beta particle, –1e
0
1
(C)
a proton, 1H
(D)
a neutron, 0n
1
Extension Question
50) Recently Alexander Valterovich Litvinenko was poisoned by radioactive
polonium-210.
a. Research who he was and why he was poisoned.
b. Find out what polonium-210 does to people.
c. Write the nuclear reaction of polonium-210 decaying into lead-206 via an
alpha decay.
Chapter 25 Nuclear Chemistry Read Chapter 25
After having read through chapter 25, respond to these conceptual questions.
51) Define the following terms:
a. critical mass
d.fusion
g.radioisotope
b.decay
e. half life
c. fission
f. transmutation
52) Make (or find) a graphical timeline of the development of modern atomic theory
with at least 10 important dates and/or discoveries.
After having read through chapter 25, respond to these practice questions.
53) Which type of radiation has a +2 charge?
a. Alpha
b. beta
c. gamma
d. neutron
54) Which type of radiation generates the highest energy – is the “hardest” to block?
a. Alpha
b. beta
c. gamma
d. neutron
55) Finish the following nuclear reactions. Tell if they are alpha or beta decays.
a.
b.
238
234
92
90
19
9
U
Th + ____
19
F  ___+ 10 Ne
c. 222
86
d.
4
Rn  ___ + 2He
210
85
0
At  ___ +-1
56) What element was the first synthesized by scientists (namely) Ernest Rutherford?
57) How many grams of sample are left after 20 minutes if 100 grams start decaying
with a half life of 5 minutes?
58) How long will it take 100 grams of radioactive sample to decay so that only 6.25
grams remain and the samples half life is 3 days?
59) How long is the half life of an isotope if 2.0 grams of sample remain from a 64
gram sample after 30 years?
After having read through chapter 25, respond to these extension questions.
60) Element number 96 is named Curium. Do you think Marie and Pierre Curie did
enough in the advancement of science to have an element named after them?
Explain.
61) Thorium-231 is a radioactive isotope. It decays in ten steps to form lead-207.
The ten steps are:. Write this decay series starting
with 231Th and progressing to 207Pb. Show each step individually.
Answers to Practice Problems
5) a Atomos are divisible.false – atomos are indivisible spheres
5b. Atomos are hard dense spheres true, they are according to Democritus
5c. Atomos have varying density – they are heterogeneous.false- they are homogeneous
5d. Changes in matter are due to the changes in atomos. False –atomos do not change
6a. All matter is made of small particles called atoms. true, it is!
6b. Atoms are divisible. True for Dalton, false for us today, p+, no and e- exist
6c. Atoms of the same element are identical true for Dalton, false for us – isotopes exist
6d. Atoms can be separated, combined or rearranged true – these are reactions
15) Who determined that electrons exist? thomson – cathode rays are electrons
16) Who determined the mass of an electron? Millikan in his oil drop experiement
17) What is the mass of an electron? 9.1 x 10-28 g
18) Who determined that the nucleus of an atom exists? Rutherford and his gold foil
19) Who determined the charge of nucleus? Rutherford and his gold foil
20) What is the charge of the nucleus? Positive
21) Who determined that neutrons exist? Chadwick
22) What is the mass of a proton? 1.67 x 10-24grams
23) What is the mass of a neutron? 1.675 x 10-24 grams
34) How many protons in calcium? Ca’s atomic # is 20, so there are 20 protons
35) How many neutrons in an atom of lithium-7? Li’s atomic # is 3, so there are 3
protons, its mass is 7, so 3 + no = 7 the # of no must be 4.
36) How many electrons in every atom of magnesium? Mg’s atomic number is 12, so
there must be 12 protons and it is an atom, so there must be 12 electrons
37)How many protons, neutrons and electrons are there in an atom of barium-136?
Barium has an atomic number of 56, so there are 56 protons and 56 electrons. Its mass
is 136 so 56 + n = 136 therefore # no is 80
38) – if you have questions on this one make sure you understand number 37 first…
Isotope
Symbol
# p+ #e - #no
Atomic
Mass
Charge
Name
Number
Number
118
tin - 118
68
0
50
50
50
118
Sn
40
K +1
19
50
Potassium-40
19
18
21
19
40
+1
9
10
10
9
19
-1
7
10
7
7
14
-3
52
52
76
52
128
0
Fluorine -19
19
F -1
9
Nitrogen -14
14
7
N
-3
128
tellurium - 128
52
Te
46)Complete this chart on the three types of radioactive decay
Type
Alpha
Beta
Gamma
Symbol



Mass (amu)
4 amu
0 amu
0 amu
Charge
+2
-1
No charge
238
47) If the radioactive atom 92U emits an alpha particle, the atom remaining is
represented by
(A)
238
92U
(B)
236
92Th
(C)
234
92U
(D)
234
90Th
234
(E) 91Pa
The alpha particle is two protons and two neutrons, so the mass will decrease by 4 and
the atomic number by 2… 238-4 = 234 92-2 = 90
30
14Si
48) What term completes this equation?
4
2
(A)2He
1
(B)1H
32
0
+ ?  16S + –1e
0
(C)1H
(D) –1e
The mass must be equal on both sides of the equation 30 + x = 32 + 0 x = 2
The atomic numbers must be equal on both sides 14 + x = 16-1 x =1
214
49) What particle is emitted when lead–214, 82Pb, undergoes natural radioactive
214
decay to bismuth–214, 83Bi?
4
(A)
an alpha particle, 2He
(C)
1
a proton, 1H
0
1
(B)
a beta particle, –1e
(D)
a neutron, 0n
The atomic number increases while the mass remains constant. The beta particle 0-1e
is the only way to show this – remember that this decay is when a neutron turns into a
proton and an electron and the electron is shot out of the nucleus.
53) Which type of radiation has a +2 charge?
a. Alpha (2 p+ and 2 no)
b. beta
c. gamma
d. neutron
54) Which type of radiation generates the highest energy – is the “hardest” to
block?
a. Alpha
b. beta
c. gamma
d. neutron
55) make sure to add the values correctly
234
4
a. 238
92
U
19
0
90
Th + 2He
c. 222
218
86
84
Rn 
alpha
b.
9
19
F  -1  + 10Ne
Beta
4
Po + 2 He
alpha
d.
210
85
210
0
At  86 Rn +- 1 
beta
56) What element was the first synthesized by scientists (namely) Ernest
Rutherford? Oxygen-17 – read your book
57) How many grams of sample are left after 20 minutes if 100 grams start
decaying with a half life of 5 minutes?
100g  50g in 5 min  25g in 10 min  12.5g in 15 min 6.25 g in 20 min
58) How long will it take 100 grams of radioactive sample to decay so that only
6.25 grams remain and the samples half life is 3 days?
100g  in 3 days 50g  25g in 6 days  12.5g in 9 days 6.25 g in 12 days
59) How long is the half life of an isotope if 2.0 grams of sample remain from a
64 gram sample after 30 years?
64g  32g 16 g  8 g 4 g  2 g there are 5 half lives in 30 years, each half life
must be 6 years long.