CHEMISTRY 108 – Help Sheet #2
Prepared by Kelly Jetzer – Fall, 2014 – Chemistry Learning Center
http://www.chem.wisc.edu/areas/clc (Resource page)
Nuggets: ionizing radiation, ionic compounds, free radicals,half-life, fission, neutron
activation, transuranium elements
Ionizing Radiation- Radiation with enough energy to ionize the medium through which it passes. Alpha,
beta, gamma and x-rays are ionizing radiation.
When ionizing radiation interacts with water, the following reactions can occur:
H2O ! [H2O•]
+
+ e
-
[H2O•]+ + H2O ! H3O+
+ HO•
Note that the dots in the reactions above represent unpaired electrons. A species which contains an
unpaired electron is called a free radical. (See below for more info on free radicals.)
Ionic compound- compound that contains ionic bonds. Ionic compounds are usually compounds
between a metal and a nonmetal. They are held together by the electrostatic attractions between the
differently charged ions. When writing the formula of an ionic compound, the positive ion goes first.
Cation- (pronounced cat-ion)- positively charged ion, usually monatomic metal ions, formed when a metal
atom loses one or more electrons. A common polyatomic cation is ammonium (NH4+).
Anion- (pronounced an-ion)- Negatively charged ions, commonly formed when a nonmetal atom gains
one or more electrons. Common polyatomic anions include:
Nitrate (NO3-1) Sulfate (SO4-2) Carbonate (CO3-2) Bicarbonate (HCO3-1) Hydroxide (OH-1)
Metals typically occur in nature as either the metal oxide, the metal sulfide, or the metal carbonate.
Free Radical- molecular species that has an unpaired electron (symbolized by a dot). Free radicals are
highly reactive. Thy can form due to ionizing radiation. Most of the damage associated with ionizing
radiation is due to free radicals.
Cancer can be caused by exposure to ionizing radiation, which damages DNA. Sometimes, this leads to
rapid replication of the damaged cell, causing a tumor. Cancer is most likely in rapidly dividing cells, such
as sex cells, hair cells, or bone marrow.
Half-life- time it takes for half of a sample of a specific isotope to decay. A sample decays to below 1% of
its original content in 7 half lives. At this point it is considered “gone.”
Number of half-lives
% of sample remaining
% of sample decayed
0
100
0
1
50
50
2
25
75
3
12.5
87.5
4
6.25
93.75
5
3.13
96.87
6
1.56
98.44
7
0.78
99.22
Emission- nucleus releases ionizing radiation to become more stable
Fission- nucleus splits into two other nuclei in response to being hit by a high energy neutron. Only some
unstable nuclei are able to do this. Fission doesn’t start on its own, but once it does, a chain reaction is
possible (if a “critical mass of the isotope is present). Most fission products are themselves radioactive.
235
***The fissionable isotope of uranium is U***
One possible fission reaction for
235
U:
235
92U
+
1
0n
!
138
56Ba
+
95
36Kr
+3
1
0n
+ energy!
Neutron activation- changing a stable nucleus into an unstable nucleus by the addition of one or more
neutrons.
Transuranium elements- Elements past uranium (have atomic number greater than 92). Created by
238
neutron activation of
U followed by beta decay.
238
1
239
239
0
92U + 0n ! [
92U] !
93Np + -1e
Critical mass- mass of fissile element necessary to sustain a chain reaction
Fission products- Nuclei (usually radioactive) left behind after fission, along with neutrons, and a lot of
energy
Fallout- radioactive nuclei left behind after a nuclear blast (uncontrolled fission). Some of them (such as
Iodine-131 and Strontium-90) readily bioaccumulate, leading to cancer.
Iodine-131 - a radioisotope of iodine that causes thyroid cancer. Can be prevented by stable iodine
supplementation before exposure to I-131. Iodine-131 is used to treat Graves Disease,
CHEMISTRY 108 – Practice Questions Week 2
Prepared by Kelly Jetzer – Fall, 2014 – Chemistry Learning Center
http://www.chem.wisc.edu/areas/clc (Resource page)
1. Name the 4 types of ionizing radiation. Describe each of them, and tell how a nucleus changes if it undergoes decay (Be specific for each type of ionizing radiation). Give a symbol for each of the three most damaging types of ionizing radiation. 2. Iodine-­‐131 is a beta emitter, with an accompanying gamma ray. A) Write the balanced equation for the decay of iodine-­‐131. B) Explain how iodine-­‐131 is used to treat Graves disease (a thyroid condition). C) The half-­‐life of iodine-­‐131 is 8 days. How long must you avoid a person who received a dose of iodine-­‐131? Explain. (Your explanation should include some math!) 3. The first step of U-­‐238’s radioactive decay series is the alpha decay of U-­‐238. A) Write the equation for this decay. B) The half-­‐life of U-­‐238 is 4.5 billion years. If I have a 100g sample of U-­‐238, how much of it will remain after 13.5 billion years? C) Could 214Po possibly be the end product of the 238U decay series? How do you know? 4. Write the chemical formula for each of the following compounds: a) calcium chloride________________ b) sodium sulfate______________ c) aluminum sulfide_______________ d) potassium nitrate ______________ e) magnesium hydroxide ____________ e) ammonium carbonate _____________ 5. Write two equations that show how ionizing radiation interacts with molecules. Circle the free radicals in each equation. 6. After 96 days, the activity of a sample of 234Th drops to 6.25% of its original activity. Calculate the half-­‐
life of 234Th. Show your work. CHEMISTRY 108 – Practice Questions Week 2 - KEY
Prepared by Kelly Jetzer – Fall, 2014 – Chemistry Learning Center
http://www.chem.wisc.edu/areas/clc (Resource page)
1. Name the 4 types of ionizing radiation. Describe each of them, and tell how a nucleus changes if it undergoes decay (Be specific for each type of ionizing radiation). Give a symbol for each of the three most damaging types of ionizing radiation. Alpha: a Helium-­‐4 nucleus (42He), atomic # ↓2, mass # ↓4 Beta: a high speed electron emitted from nucleus (0-­‐1e), atomic #↑1 Gamma: VERY energetic electromagnetic radiation (00ɣ), no change in atomic# or mass# X-­‐ray: high energy electromagnetic radiation – not associated with nuclear decay 2. Iodine-­‐131 is a beta emitter, with an accompanying gamma ray. A) Write the balanced equation for the decay of iodine-­‐131. 131
131
0
0
53I ! 54Xe + -­‐1e + 0ɣ B) Explain how iodine-­‐131 is used to treat Graves disease (a thyroid condition). Graves disease involves an overactive thyroid. The patient receives doses of I-­‐131, which is incorporated into the thyroid, where it undergoes decay, emitting radiation, which destroys some of the overactive thyroid tissue. C) The half-­‐life of iodine-­‐131 is 8 days. How long must you avoid a person who received a dose of iodine-­‐
131? Explain. (Your explanation should include some math!) It’s gone after 7 half-­‐lives. 8*7= 56 days 3. The first step of U-­‐238’s radioactive decay series is the alpha decay of U-­‐238. A) Write the equation for this decay. 238
234
4
92U ! 90Th + 2He B) The half-­‐life of U-­‐238 is 4.5 billion years. If I have a 100g sample of U-­‐238, how much of it will remain after 13.5 billion years? 13.5 billion years = 3 half-­‐lives. After 3 half-­‐lives, 12.5% remains. 12.5 g C) Could 214Po possibly be the end product of the 238U decay series? How do you know? No. All isotopes of elements beyond atomic# 83 are radioactive, so 214Po can’t be stable. 206Pb is the end product of the 238U decay series. 4. Write the chemical formula for each of the following compounds: a) calcium chloride____CaCl2___ b) sodium sulfate____Na2SO4__________ c) aluminum sulfide__Al2S3_________ d) potassium nitrate ____KNO3__________ e) magnesium hydroxide __Mg(OH)2___ e) ammonium carbonate _(NH4)2CO3______ 5. Write two equations that show how ionizing radiation interacts with molecules. Circle the free radicals in each equation. H2O ! [H2O•]+ + e[H2O•]+ + H2O ! H3O+
+ HO•
6. After 96 days, the activity of a sample of 234Th drops to 6.25% of its original activity. Calculate the half-­‐life of 234
Th. Show your work. It takes 4 half-­‐lives for the activity to drop to 6.25%. If 96 days = 4 half-­‐lives, then t1/2= 24 days