Name: KEY
Per:
Date:
Chemistry
Study Guide
Study Guide for Unit 2 Exam, part II: Atoms
Format: Multiple choice, free response. You will need a pencil and a calculator. A periodic table will be handed
out. The spaces below are for you to write down notes, definitions, etc.
Learning Targets:
2D) describe atomic structure to compare and contrast atoms of the same element and atoms of different elements
2E) predict and explain which isotope of an element is the most abundant; calculate the average atomic mass of
an element.
2F) compare and contrast nuclear radiation types and write balanced nuclear equations to represent alpha, beta
and electron capture processes; use atomic structure to predict if a nucleus is stable or will undergo alpha
decay, beta decay or electron capture.
2G) explain and interpret graphic representations of half-life, calculate quantity using rate tables and known halflives
2H) compare and contrast the processes of fission and fusion, including their potential as future energy sources
Vocabulary: atom, subatomic particles, protons, neutrons, electrons, nucleus, electron cloud, element, atomic
number (Z), mass number (A), isotope, atomic mass, average atomic mass, atomic mass unit (amu), relative
abundance, percent abundance, weighted average, radioisotopes, radioactivity, ionizing radiation, nonionizing radiation, alpha radiation/decay & alpha particles, beta radiation/decay & beta particles,
positron emission, electron capture, gamma radiation, transmutation, band of stability, half-life, fission,
fusion
Unit 2: Stars and Atoms
1
Practice problems (review problems in the notes as well; not everything on the exam is covered here.)
1. The Z number of silver-108 is 47.
2. The A number of silver-108 is 108.
3. Silver-108 has 47 protons, 61 neutrons, and 47 electrons.
4. Write silver-108 in nuclear notation (isotope notation).
𝟏𝟎𝟖
𝟒𝟕𝑨𝒈
5. Calculate the atomic weight of chlorine based on the following data.
Chlorine-35: 34.969 amu, 75.77%
34.969 x 0.7577 = 26.50
Chlorine-37, 36.966 amu, 24.23%
36.966 x 0.2423 = 8.957
26.50 + 8.957 = 35.46 amu
(matches with 35.45 on periodic table)
6. Using only your periodic table, what is likely the most abundant isotope of phosphorus? phosphorus-31
Draw and label a Bohr model of this isotope. Label and list the number of the subatomic particles.
blue circles are electrons.
7. Write a balanced nuclear equation for each of the following processes.
a. Cobalt-65 emits beta particles.
#$
!"Co
→
'
%&e
+ #$
!(Ni
b. Bismuth-185 undergoes positron emission.
&($
()Bi
→
'
*&e
+ &($
(!Pb
c. Iodine-118 captures an electron.
&&(
$)I
d.
+ %&'e ⟶
&&(
$!Te
Francium-220 undergoes alpha decay and releases gamma radiation.
!&#
+
8. Write a clai !!'
("Fr → !He + ($Atm, evidence, reasoning paragraph (at least 3 sentences) where you
predict the decay process of scandium-48. Your answer must include a balanced nuclear equation.
Scandium-48 likely undergoes beta decay.
Scandium’s average atomic weight is 44.96, which is smaller than 48. So scandium-48 has too many
neutrons. Some neutrons need to turn into protons, which occurs in beta decay.
48
0 48
21Sc→ -1e+ 22Ti
Titanium’s average atomic weight is 47.87, so titanium-48 is probably stable, therefore beta decay is
plausible for scandium-48.
Unit 2: Stars and Atoms
2
9. What type of decay will curium-243 undergo? Write a claim, evidence, reasoning paragraph (at least 3
sentences) Your answer must include a balanced nuclear equation.
Claim: Curium-243 will likely undergo alpha decay.
Evidence: Curium atoms have 96 protons, which is more than 82, the maximum amount of protons that can
be stabilized by neutrons.
!+)
,#Cu
→ +!He +
!),
,+Pu
Reasoning: Atoms with more than 82 protons tend to undergo alpha decay because alpha decay decreases
both protons and neutrons, which will eventually return the atom to the band of stability. Because curium243 has more than 82 protons, it may undergo alpha decay.
(Another option is beta decay; many heavy atoms with more than 1.5 neutrons for every proton undergo
beta decay, and curium-243 has a neutron-to-proton ratio of 1.53 (too many neutrons)).
10. A scientist has a 400. g sample of the radioisotope, phosphorus-32. The half-life of phosphorus-32 is 14.3
days. What mass of the original sample will remain after 71.5 days?
71.5 days / 14.3 days = 5 half lives
400. g/ 2/ 2/ 2/ 2/ 2 = 12.5 g P-32
OR:
half-lives
0
1
2
3
4
5
time (days)
0
14.3
28.6
42.9
57.2
71.5
amount (grams)
400.
200.
100.
50.0
25.0
12.5
12.5 g P-32
11. After 3.90 minutes, a sample of barium-122 has decreased to 25.0% of its original mass. What is the halflife of barium-122?
100%/2 = 50%
50% / 2 = 25%
2 half lives have passed.
3.90/2 = 1.95 minutes
12. A certain radioisotope has a half-life of 12.0 hours. What percentage of a sample will remain after 2.00
days?
2.00 days = 48.0 hours
48.0 hours/12.0 hours = 4 half lives
100/2/2/2/2 = 6.25% remaining
13. In 2-3 complete sentences, describe one application of nuclear chemistry.
See notes.
14. In 2-3 complete sentences, describe a different application of nuclear chemistry.
See notes.
Unit 2: Stars and Atoms
3