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Chemistry Regents Page 1 of 7Mr. Markic
Chapter 25 - Nuclear Chemistry
The study of ____________ ____________ and their uses in chemistry
Radiation -• The penetrating rays & particles emitted by a radioactive source
Radioactivity -• Process that occurs when nuclei change ____________Radioisotopes -• Atoms containing ____________ ____________
Recall… What are isotopes?o
How do nuclear reactions differ from chemical reactions?
Chemical Reactions• Atoms become stable by ____________or
____________electrons • Rate ____________changed by catalysts,
temperature, pressure, etc. • Mass & charge ____________
Nuclear Reactions• Nuclei become stable by undergoing changes
that ____________of energy • Rate ____________be changed• Charge conserved, mass ___________________
o A ____________small amount of mass is converted into energy
Nuclear Stability• Most nuclei are stable • The stability of a nucleus depends on its neutron to proton
____________• The stable nuclei are in the ‘________________________’
Radioactive Decay• Occurs in atoms with too _______or too _______neutrons • The nucleus will attempt to become more stable by releasing energy
through ______________• Transmutation -
o when the unstable nucleus of one element is ____________ into a stable nucleus of a different element
o Occurs naturally and artificially
Types of Radioactive Decayo Alpha particles, o Beta particles, o Positron emission o Gamma rays,
Chemistry Regents Page 2 of 7Mr. MarkicAlpha Decay – α• Gives off ____________ particles (helium nuclei) • Occurs when the neutron: proton ratio is low• A radioactive element gives off 2 protons and 2 neutrons
o The charge on the nucleus ________________________• Alpha particles do not travel far & are not very penetrating due to their large mass and charge
o Sheet of paper or surface of skin stops them
24094Pu → 236
92U + 42He (α)
o Atomic # - o # of protons -o Mass # -o # of neutrons -
Beta Decay – β• Gives off ____________ particles (electrons)• Occurs when the neutron: proton is high• A neutron breaks apart into a proton, which stays in the nucleus, and an electron which is released
o 10n → 1
1H + 0-1e (β)
o Charge on the nucleus ________________________• More penetrating than α particles
o Can pass through paper, but are stopped by aluminum foil or thin pieces of wood
22888Ra → 228
89Ac + 0-1e (β)
o Atomic # -o # of protons -o Mass # -o # of neutrons -
Positron Emission• Gives off a ____________ (positive electron)• Occur when the neutron: proton is low• A proton breaks apart into a neutron, and a unit of positive charge
o 11p → 1
0n + 0+1e (positron)
o Charge on the nucleus ________________________
2211Na → 22
10Ne + 0+1e
o Atomic # -o # of protons -o Mass # -o # of neutrons -
Chemistry Regents Page 3 of 7Mr. MarkicGamma Decay – γ• Gives off high energy photons called ________________________• _____________________________________________ • Very dangerous - extremely penetrating
o Pass easily through paper, wood, & the human bodyo Some can be stopped by several meters of concrete or several centimeters of lead
24094Pu → 240
94Puo Atomic # -o # of protons -o Mass # -o # of neutrons -o Nucleus changes only in its energy state
Summary of Radiation
Particle Mass Charge Symbol Penetrating Power
Alpha 4 amu 2+ 42He, α Low
Beta 0 amu 1- 0-1
e, β ModeratePositron 0 amu 1+ 0
+1e Moderate
GammaRay
0 amu None γ High
Nuclear Equations• Similar to chemical equations…• Mass and charge must balance on both sides
• 147N + 4
2He → 178O + 1
1H
• By using the concept of conservation of charge and mass number, you can identify a missing particle in an equation.
Sample Exercises1. What product is formed when radium-226 undergoes alpha decay?
2. What element undergoes alpha decay to form lead-208?
3. What product is formed when Mg-27 decays by beta emission?
Chemistry Regents Page 4 of 7Mr. Markic4. 3
1H _____ + 0-1e
5. 93Li 9
4Be + _____
6. 146C 0
-1e + _____
7. 24195Am 4
2He + _____
8. 167N 16
6O + _____
9. What forms when francium-220 decays?
10. What forms when potassium-37 decays?
11. What forms when potassium-42 decays?
12. 63Li + 1
0n 42He + _____
13. 2713Al + 4
2He _____ + 01e
14. 2714Si 0
-1e + _____
15. 21483Bi 4
2He + _____
16. 6629Cu 66
30Zn + _____
17. 23592U 90
38Sr + _____ + 10n + 40
-1e
Half-Life• Time required for ____________ of the nuclei of a radioactive sample to decay into products
• After each half-life, __________of the existing radioactive atoms have decayed into atoms of a new element
Chemistry Regents Page 5 of 7Mr. MarkicTable N• Each element has a characteristic half-life
• Anywhere from a fraction of a second to billions of years
• ½ life is ________________________
Uses for Half-Life• Dating• Nuclear medicine
Half-Life Calculations• No formula; make a ________________________ chart• Always start with time = ____________• If no mass is given, start with ________________________
Sample Problems1. Most chromium atoms are stable, but Cr-51 is an unstable isotope with a half-life of 28 days.
a. What fraction of a sample of Cr-51 will remain after 168 days?
b. If a sample of Cr-51 has an original mass of 52.0g, what mass will remain after 168 days?
2. How much was present originally in a sample of Cr-51 if 0.75mg remains after 168 days?
3. According to Reference Table N, how much of a 100. microgram (μg) sample of nitrogen-16 will remain after 28.52 seconds of decay?
4. In 5.49 seconds, 1.20g of Ar-35 decay to leave only 0.15g. What is the half-life of Ar-35?
5. Na-24 has a half-life of 15 hours. How much Na-24 will remain in an 18.0g sample after 60 hours?
Chemistry Regents Page 6 of 7Mr. Markic6. How many half-lives are required for a radioisotope to decay to 1/32 of its initial value?
7. What fraction of 226Ra will be left after 4797 years?
Artificial Transmutations• Particle Accelerators -
o Collision of a proton or α particle with a target nucleuso Uses magnetic or electrostatic fields to accelerate particles & overcome the repulsive forces
• Neutron Collisions -o Occurs when a neutron collides with a target nucleuso Used to prepare radioactive nuclei from stable nuclei
▫ 23892U + 1
0n → 23992U
▫ 5927Co + 1
0n → 6027Co
▫ 3216S + 1
0n → 3215P + 1
1H
Nuclear Fission• ____________ of the nucleus into smaller fragments
o Occurs when the nucleus is bombarded with ____________
o Uranium-235 and Plutonium-239 are the only fissionable isotopes
________________________________________________
• Releases huge amounts of ____________• Very exothermic
o 1 kg U-235 = 20,000 tons of dynamiteo Atomic bombs & nuclear reactors
Nuclear Reactors• Uses controlled fission• Energy from fission reaction heats the coolant• Heated coolant is used to produce steam• Steam turns a turbine• Turbine drives a generator to produce electricity
Chemistry Regents Page 7 of 7Mr. Markic
Nuclear Fusion• Light nuclei ____________ to produce a nucleus of greater mass• Solar fusion – H nuclei fuse to make He nuclei
________________________________________________
Fusion as an Energy Source• Produces ____________ energy than fission• Occurs only at high temperatures (over 40,000,000ºC) • More appealing than fission because:
o Availability/low cost of light isotopeso Products are generally not ________________________
Detecting Radiation• Radiation ____________ be seen, heard, felt, or smelled• Ionizing radiation -
o radiation with enough energy to knock electrons off atoms of the bombarded substance to produce ions
o Can be detected by Geiger counters, scintillation counters, and film badges
Using Radiation• Medicine -
o Diagnostic toolso Treatment for cancero Help to determine mechanisms for chemical
reactionso Trace movements of atoms in biological
systems
• Radiation in the body should:o Have a ____________ half-lifeo Be ____________ eliminated from the body
Other Uses of Radiation• Tracers -
o Any radioisotope used to follow the path of a substance
o Ex. Used in agriculture to test the effects of herbicides, pesticides, and fertilizers
• Dating -o Using half-lives, ‘age’ of objects can be
determinedo C-14 → C-12: o U-238 → Pb-206:
• Industrial Applications –o Used to measure the thickness or
strength of a material based on radioactive absorption
• Food Irradiation –o Kills insects, bacteria, & moldo Prevents the ‘sprouting’ of fruits &
vegetables