Unit 11: Nuclear Chemistry - PowerPoint Presentation

Unit 11: Nuclear ChemistryTopic 1: Natural Radioactivity Objective: Identify the 4 modes of decay, use Table N and O to identify natural radioactive decay and write nuclear equations, identify the similarities and differences between physical, chemical, and nuclear reactions, identify what transmutation is

I. Natural Radioactivity and Stability Nuclear Stability: the larger (more massive) a nucleus is, the harder it is for it to stay togetherWhen a nucleus is ______________________, it gives off decay particles and changes ________________________. This is known as ___________________________Atoms with an atomic number of 1 through 83 have at least one stable isotope, but… ________________________________________________________ radioactive from one element to another Natural decay or natural transmutation All isotopes of elements above 84 are more reactive and are natural radioisotopes

II. Four Modes of Decay Natural Radioactivity: _________________________________ of the _________________ of an atom, with the emission of _________________________________ Modes of Decay (See Table ______) spontaneous disintegration nucleus Particles and/or energy O

II. Four Modes of Decay Type of Decay Symbol Charge Mass Penetration Strength

II. Four Modes of Decay Transmutations: Penetration: When a nucleus decays into a new and different nucleus (also called radioactive decay) How far into a material the radioactive particle will go

III. Nuclear Equations Types of Reactions:Physical Reaction: H2O (s)  H2O (l) Same? Different?   Chemical Reaction: 2H 2 (g) + O2(g)  2H2 O (l) Same? Different?Nuclear Reaction: 16 7N 0-1e + 16 8 O Same? Different? Compound & mass (and charge) Phases (s  l) Mass and # of same atoms (and charge) compounds Mass and chargeelements

III. Nuclear Equations Natural Transmutations (Decay) always has only ___________________________________Use Table ____ to identify the type of decay for specific nuclide Use Table ____ to identify notation of each decay mode One reactant and two products N O

III. Nuclear Equations Show the natural radioactivity decay of:Francium – 220 2. Gold – 198 3. Neon – 19

III. Nuclear Equations Show the natural radioactivity decay of:4. Iodine– 131 5. Uranium– 223 Potassium – 37 How do you balance with nuclear equations? Sum of charges and mass numbers are balanced

Unit 11: Nuclear ChemistryTopic 2: Half-Life Objective: Solve various half-life problems based on given data.

IV. Half-Life Problems Half-Life: the period of time that must go by for half of the nuclei in the sample to undergo decay.During a half-life period: half of the radioactive nuclei in a sample decays _________________________The half-life of many radioactive isotopes can be found on Table_____ Solving half-life problems strategies: 1. Identify what nuclide (isotope) is the problem asking for? (go to table N if necessary) 2. What is the half-life of the nuclide? 3. How much time has passed? How many half lives does this represent? How many cuts in half were there?4. Cut mass in half the required number of times to a new, more stable nuclei N

IV. Half-Life Problems Examples:1. What mass of I-131 remains 32 days after a 100 gram sample is obtained?2. What fraction of 1 gram sample of carbon – 14 would remain after 17,190 years?

IV. Half-Life Problems Examples:3. Analysis of charred wood at a prehistoric campsite reveals that it contains 1/4 of the amount of carbon-14 that is found in living tissues. How old is the campsite? 4. The half-life of Rn-222 (a carcinogenic house pollutant) is 3.8 days. If today your basement contains 20 grams of Rn-222, how much will remain after 19 days, assuming no more leaks in?

IV. Half-Life Problems Examples:5. The half-life of Tc-99m* (used to locate brain tumors) is 6.0 hours. If 10. Micrograms are left after 24 hours, how much Tc-99m was administered? 6. A radioactive sample is placed next to a Geiger counter and monitored. In 20.0 hours, the counter’s reading goes from 500 counts/minute to 125 counts/minute. How long is the half-life?

IV. Half-Life Problems Examples:7. The oldest rocks on Earth have been found to contain 25% of their original mass of U-238. What is the age of these rocks?

Unit 11: Nuclear ChemistryTopic 3: Artificial Transmutations Objective: Write artificial transmutation reactions, identify the similarities and differences between artificial/natural decay, and identify the similarities and differences fission/fusion reactions.

V. Artificial Transmutations   Remember when writing/ balancing nuclear reactions: The sum of the charges and mass numbers must be equal on both sides Example 1: 9 4 Be + _____  12 6 C + 10 nExample 2: 2713Al + 42 He  1 0 n + _____ “man made” reaction caused by hitting a nucleus with a high-energy particle, such as a neutron or alpha particle 4 2 He 31 15 P

V. Artificial Transmutations  PRACTICE 1 – 5 on the front of Worksheet 3

V. Artificial Transmutations   Similarities and Differences between Natural Transmutations and Artificial Transmutations Unique to Natural Decay Common to Both Unique to Artificial Transmutation - Single UNSTABLE reactant decays into a decay particle and new, more stable nucleus - STABLE nucleus and particle bullet collide to produce NEW products - Mass and charge conserved - Both form new elements- Both produce energySmaller amountLarger amount

VI. Fission and Fusion Fission -     Example: (ANIMATION ) - SPLITTING of a nucleus into smaller atom(s), neutrons, and ENERGY (EXOTHERMIC) - Commonly used isotopes are Uranium-235 and Plutonium-239 235 92 U + 1 0 n  92 36 Kr + 141 56Ba + 3 10n + ENERGY

VI. Fission and Fusion Fusion-     Example: ( ANIMATION ) - Occurs when atoms COMBINE to produce a nucleus of GREATER mass and ENERGY (EXOTHERMIC) - Gives off MUCH more energy than fission 3 1 H + 2 1 H  4 2 He + 10n + ENERGY

VII. Where does Energy come from? Both reactions sacrifice nuclear mass to form energy (E= mc2) the “missing mass” in a nuclear reaction is called the mass defect and is the energy released in the reaction VIDEO How are nuclear power plant works?

V. Artificial Transmutations   Similarities and Differences between Nuclear Fission and Fusion (WRITE SMALL) Unique to Nuclear Fission Common to Both Unique to Nuclear Fusion - SPLITS nucleus to SMALLER particles - Artificial transmutation - Used to produce electricity in powerplants - Produces radioactive waste - COMBINES two small nuclei together to form a LARGER one - Used by stars - Produces essentially no radioactive waste Both generate energy the same way (Convert mass  energy)Less energy more energy

Unit 11: Nuclear ChemistryTopic 4: Uses and Dangers of Radioisotopes Objective: Understand the benefits and risks of nuclear reactions, identify specific uses of common isotopes

Uses/benefits of Radioisotopes - Dating : Carbon – 14 (C-14) is measured in dead organism to find out when it was last alive based on its ½ life Medical : Certain radioisotopes are useful because they contain SHORT HALF LIVES and are QUICKLY REMOVED from the body Iodine – 131 – used to detect and treat thyroid cancer Cobalt – 60 – emits gamma rays that can kill cancer Technetium 99 – detects cancerous tumors

Radiation Risks(WRITE SMALL) - Large amounts of radiation given off by isotopes can cause serious illness and death and environmental damage. Nuclear Power Plant : decay products have LONG half-lives and are difficult to store and dispose of accidents can release harmful radioactive waste into air and water Chernobyl, Ukraine (1986)