Name: Regents Chemistry: Mr. Palermo Notes: Unit 14 Nuclear Chemistry www.mrpalermo.com
Name: KEY IDEAS: Stability of isotopes is based in the ratio of neutrons and protons in its nucleus. Although most nuclei are stable, some are unstable and spontaneously decay, emitting radiation. (3.1o) Each radioactive isotope has a specific mode and rate of decay (half-life). (4.4a) A change in the nucleus of an atom that converts it from one element to another is called transmutation. This can occur naturally or can be induced by the bombardment of the nucleus by high-energy particles. (5.3a) Spontaneous decay can involve the release of alpha particles, beta particles, positrons, and/or gamma radiation from the nucleus of an unstable isotope. These emissions differ in mass, charge, ionizing power, and penetrating power. (3.1p) Nuclear reactions include natural and artificial transmutation, fission, and fusion. (4.4b) There are benefits and risks associated with fission and fusion reactions. (4.4f) Nuclear reactions can be represented by equations that include symbols which represent atomic nuclei (with the mass number and atomic number), subatomic particles (with mass number and charge), and/or emissions such as gamma radiation. (4.4c). Energy released in a nuclear reaction (fission or fusion) comes from the fractional amount of mass converted into energy. Nuclear changes convert matter into energy. (5.3b) Energy released during nuclear reactions is much greater than the energy released during chemical reactions. (5.3c) There are inherent risks associated with radioactivity and the use of radioactive isotopes. Risks can include biological exposure, long-term storage and disposal, and nuclear accidents. (4.4e) Radioactive isotopes have many beneficial uses. Radioactive isotopes are used in medicine and industrial chemistry, e.g., radioactive dating, tracing chemical and biological processes, industrial measurement, nuclear power, and detection and treatment of disease. (4.4d) www.mrpalermo.com
UNIT 14: NUCLEAR CHEMISTRY WWW.MRP AL ERMO.C O M LESSON 14.1 NUCLEAR CHEMISTRY WWW.MRP AL ERMO.C O M Objective: By the end of this video you should be able to: Atomic Notation: Identify the type of nuclear decay mode Construct nuclear equations for alpha, beta and positron decay Determine the penetrating power of each emission Subtract atomic number from mass number to find the NEUTRONS ISOTOPES: Same element different number of neutrons Radioactive Decay Stability of Nuclei In the simplest terms, an unstable (radioactive) nucleus of an atom breaks apart into smaller parts. Transmutation: Occurs when the unstable element (radioactive) decays into new element. ALWAYS TURNS INTO A MORE STABLE ELEMENT Large Atoms - Elements with an atomic number greater than 83 are naturally unstable (radioactive.) Small atoms - When an atom s mass is not its typical mass on the periodic table - C-13 & C-14 1
RADIOACTIVITY Is due to the proton-neutron ratio. The band of stability refers to atoms that are stable due to stable proton-neutron ratios. Table O- Types of Decay (Radiation) Natural Transmutation When nuclei of unstable atoms emit radiation (Table O) naturally & form a new substance Number on the upper left is the mass Number on the lower left is the charge REMEMBER.DON T BREAK THE LAW - The Laws of Conservation of Mass & Charge - in a nuclear reaction, Mass & Charge must be conserved Table N: Decay Modes for Selected Nuclides RADIOACTIVITY- BETA DECAY Atoms above the belt have too many neutrons and will beta decay due to this. The beta particle is an electron created when a neutron decays. 131 I 1 or 1 e 131 53 54 Xe + e 1 2
Example: Beta decay: 234 Th undergoes beta decay 234 Th e + 234 Pa 9-1 91 The total mass on the left must equal the total mass on the right (234 = + 234) The total charge on the left must equal the total charge on the right (9 = -1 + 91) Example Construct the nuclear decay equation for Carbon-14 (remember that mass and charge must be conserved) Check your understanding Can you identify the type of nuclear decay mode Can you construct nuclear equations for beta and decay RADIOACTIVITY- POSITRON EMISSION Atoms below this belt have too many protons and positron decay. e +1 or +1 The positron is the opposite of a beta particle. 5 + 1 e 11 11 6 C B Example: Positron emission: 37 K undergoes positron decay Example: 37 K e + 37 Ar 19 +1 18 Construct the nuclear decay equation for Calcium-37 (remember that mass and charge must be conserved) The total of the mass numbers on the left must equal the total on the right (37 = + 37) The total charge on the left must equal the total charge on the right (19 = 1 + 18) 3
Can you identify the type of nuclear decay mode Can you construct nuclear equations for positron decay Radioactivity- Alpha decay Atoms with 82 or more protons alpha decay (too many protons and neutrons) Alpha particles are weak due to their mass. Alpha particles are the helium nuclei. 4 He 4 2 or 2 α 238 92 U 234 4 9 Th + 2 He Example: Alpha decay: 238 U undergoes alpha decay 238 U 4 He + 234 Th 92 2 9 The total mass on the left must equal the total mass on the right (238 = 4 + 234) The total charge on the left must equal the total charge on the right (92 = 2 + 9) Example: Complete the example problems below showing ALPHA DECAY (remember, CHARGE and MASS must be conserved!) Can you identify the type of nuclear decay mode Can you construct nuclear equations for alpha decay Radioactivity- Gamma decay Strongest particle. Accompanies most decay. Usually not written due to the fact that it cannot change the mass or charge of any of the species. 4
Penetrating Power Most penetrating power Least penetrating power Radiation is charged: Can be separated by a magnetic field Can you determine the penetrating power of each emission You must be able to: Differentiate between artificial and natural transmutation Identify the type of nuclear decay mode Construct nuclear equations for alpha, beta and positron decay Determine the penetrating power of each emission LESSON 14.2 HALF LIVES WWW.MRP AL ERMO.C O M 5
Objective: By the end of this lesson you should be able to: HALF-LIFE Calculate given two of the three variables the: amount remaining the fraction remaining the half life number of half lives the original mass of a radioactive isotope Time elapsed Half Life: is the time it takes for ½ of the atoms of a radioisotope to decay. Calculating Half Life After one half life 5% or ½ the radioactive element is still present. After two half lives 25% or 1/4 the radioactive element is still present. After three half lives 12.5% or 1/8 the radioactive element is still present. This continues forever, the number will never be zero. The half lives are listed on Table N. Table N- Half life Time The SHORTER THE HALF LIFE of an isotope the LESS STABLE it is. The LONGER THE HALF LIFE of an isotope the MORE STABLE it is. 6
Example: Amount Remaining If a sample of I-131 has an original mass of 52.g what mass will remain after 4 days? HALF LIFE PROBLEMS Example: Amount Remaining If a sample of I-131 has an original mass of 64.g what mass will remain after 32 days? 1. Determine the number of half lives that have taken place using table N Total 2. Cut original mass in half by the # of half lives (Mass) 64 32 16 8 4 Time elapsed Half life time from Table N 4g of I-131 remain = 32 8 = 4 Cut in half 4 times Practice If a sample of Cs-137 has an original mass of 52.g what mass will remain after 15 years? 52. 26. 13. 6.5 3.25 1.63 1 2 3 4 5 After 15 years, 1.63g of Cs-137 remain Total Time elapsed = 15 Half life time from Table N 3 = 5 Cut in half 5 times (# of Half Lives) Example: Fraction Remaining If a sample of Cs-137 has an original mass of 52.g what fraction will remain after 15 years? Practice If a sample of Fe-53 has an original mass of 52.g what fraction will remain after 25.5 minutes? Same set up but you Half the fractions instead of the mass Total Time elapsed = 15 Half life time from Table N 3 = 5 Cut in half 5 times Same set up but you Half the fractions Total Time elapsed = 25.5 = 3 Half life time from Table N 8.51 Cut in half 3 times 1 1/2 1/4 1/8 1/16 1/32 1 2 3 4 5 1 1/2 1/4 1/8 1 2 3 After 15 years, 1/32 of Cs-137 remain After 25.5 minutes, 1/8 of Fe-53 remains 7
Example: Number of half-lives Can you calculate given two of the three variables the: - amount remaining - the fraction remaining How many half-life periods will it take for 5 grams of Tc-99 to decay to 6.25g? Find the number of half lives by halving the original mass until you get to the final mass 5. 25. 12.5 6.25 1 2 3 It takes 3 half-life periods for TC-99 to decay to 6.25 grams Practice: Example: half-life How many half-life periods will it take for 1 grams of I-131 to decay to 25g? Find the number of half lives by halving the original mass until you get to the final mass 1 5 25 1 2 What is the half-life of a 5 gram sample of a radioactive element if 125 grams remains after 2 hours? 1. Find the number of half lives by halving the original mass until you get to the final mass 5 25 125 1 2 = 2 half life periods 2. Divide the total time elapsed by the number of half life periods you calculated in step 1. It takes 2 half-life periods for I-131 to decay to 25g Total Time elapsed Half life time from Table N = 2 x = 2 Half life periods 2/2 = 1 hours Practice Check your understanding What is the half-life of a 5 gram sample of a radioactive element if 125 grams remains after 2 hours? 1. Find the number of half lives by halving the original mass until you get to the final mass 5 25 125 1 2 = 2 half life periods Can you calculate given two of the three variables the: - the half life - number of half lives 2. Divide the total time elapsed by the number of half life periods you calculated in step 1. Total Time elapsed Half life time from Table N = 2 x = 2 Half life periods 2/2 = 1 hours 8
Example: Original Mass The half life of Tc-99 (used in brain tumors) is 6 hours. If 1 micrograms are left after 24 hrs, how much was administered to the patient originally? 1. Divide the times to obtain your amount of half life periods Total Time elapsed 24 Half life = = 4 periods Half life time from Table N 6 2. Work backwards and double the mass 4 times 16 8 4 2 1 4 3 2 1 The original mass was 16 micrograms Practice: After 37 hours, 2g remains unchanged from a sample of K-42. How much was in the original sample? Total Time elapsed Half life time from Table N 37 = = 3 12.36 Half life periods 8 4 2 1 3 2 1 The original mass was 8g micrograms Example: Time Elapsed How long will it take for a 4 grams sample of P-32 to decay to 5 grams? MORE EXAMPLES: 1. Find the half lives by dividing the original mass in half until it hits your final mass. 4/2 = 2/2 = 1/2 = 5 3HL 2. Look up the half live on table N and multiple that time by the number of half lives you calculated. 14.3 days * 3 = 42.9 days Can you calculate given two of the three variables the: - the original mass of a radioactive isotope - Time elapsed REMEMBER YOU ONLY HALF MASS YOU NEVER HALF TIME!!!!!! 9
You must be able to: Calculate given two of the three variables the: - amount remaining - the fraction remaining - the half life - number of half lives - the original mass of a radioactive isotope - Time elapsed LESSON 14.3 NUCLEAR FISSION VS FUSION WWW.MRP AL ERMO.C O M Objective: By the end of this video you should be able to: Differentiate between natural and artificial transmutation Distinguish between fusion and fission reactions Compare the advantages and disadvantages of fusion and fission reactions Artificial Transmutation A transmutation that occurs from bombarding a nucleus w/ high energy particles ARTIFICIAL VS NATURAL TRANSMUTATION Artificial Always 2 reactants Not spontaneous Natural Always 1 reactant Spontaneous Can you differentiate between natural and artificial transmutation 1
Nuclear Reactions If you add the actual masses of all the protons, neutrons and electrons in an atom and compare it to the atom s actual mass, mass is lost. This is known as mass deficit. Mass is converted to energy! E=mc 2 The energy holds the subatomic particles together and is called the binding energy. When these reactions occur, small amounts of mass can be created into LARGE amounts of energy. This energy can be harvested in fission and fusion reactors for everyday energy use. FISSION REACTIONS A neutron is shot at a radioactive source which splits producing energy. 1 n + 235 U --> 236 U --> 142 Ba + 91 Kr + 3 1 n + energy 92 92 56 36 If the number of neutrons released is not controlled a chain reaction will occur. This is the type of reaction used in nuclear bombs. Chain Reaction A series of reactions where each reaction is initiated by the energy produced in the previous reaction NOTE: ENERGY is also produced in the above nuclear reaction Fission Reactors The reaction s energy is converted to steam which turns and turbine system, creating electrical energy from nuclear energy. Fission Reactors Fuel rods contain the fissionable radioactive source (critical mass) Control rods can regulate the neutrons absorbed (controlling the chain reaction.) 11
Nuclear power In America, about 2% electricity generated by nuclear fission Imagine: - Nuclear-powered car - Fuel = pencil-sized U-cylinder - Energy = 1 2-gallon tanks of gasoline - Refuel every 1 weeks (about 2 years) FUSION REACTIONS Involves the combining (fusing) of nuclei to produce heavier ones. Ex. 2 H + 3 H 4 He + 1 n Hydrogen atoms combine to form helium in a star. How do they know the Sun is made up of Helium? Observe helium s bright line spectrum from the sun Check your understanding Can you distinguish between fusion and fission reactions FUSION REACTIONS ADVANTAGES Produces more energy Materials more readily available Less waste DISADVANTAGES Too Expensive Can you compare the advantages and disadvantages of fusion and fission reactions Less danger (no chain reaction) 12
You should be able to: Differentiate between natural and artificial transmutation Distinguish between fusion and fission reactions Compare the advantages and disadvantages of fusion and fission reactions LESSON 14.4 BENEFITS & RISKS OF NUCLEAR POWER WWW.MRP AL ERMO.C O M Objective: By the end of this video you should be able to: Identify specific uses of some common radioisotopes Identify the risks/benefits of radioactivity USES OF RADIOACTIVE ISOTOPES DATING MATERIALS Am-241 is used in Smoke detectors Carbon-14 used to date organic remains Uranium used to date rocks 13
MEDICAL APPLICATIONS Must have short half-life and quickly eliminated from body I-131 thyroid (treat hyperthyroidism) Co-6 used to treat cancer Medical Applications: Tc-99 used to detect tumors Can you identify specific uses of some common radioisotopes DANGERS/RISKS OF RADIOACTIVITY Damage to tissue Gene mutation Pollution due to radioactive wastes Accidents from nuclear reactors The fission reaction produces radioactive waste that must be stored. Currently the waste is placed in large lead boxes under ground around the country. FISSION 14
YUCCA MOUNTAIN The Yucca Mountain, in Nevada, is a large long term storage facility for nuclear waste and testing. Can you identify the risks/benefits of radioactivity You should be able to: Identify specific uses of some common radioisotopes Identify the risks/benefits of radioactivity 15