Nuclear Chemistry Structure and Stability of Nuclei, Fission, Fusion, and Radiation.
Post on 28-Dec-2015
Nuclear ChemistryStructure and Stability of Nuclei, Fission, Fusion, and Radiation
Standards11. Nuclear processes are those in which an atomic nucleus changes, including radioactive decay of naturally occurring and human-made isotopes, nuclear fission, and nuclear fusion. As a basis for understanding this concept:a. Students know protons and neutrons in the nucleus are held together by nuclear forces that overcome the electromagnetic repulsion between the protons.
11. b. Students know the energy release per gram of material is much larger in nuclear fusion or fission reactions than in chemical reactions. The change in mass (calculated by E = mc2 ) is small but significant in nuclear reactions.
11. c. Students know some naturally occurring isotopes of elements are radioactive, as are isotopes formed in nuclear reactions.
11. d. Students know the three most common forms of radioactive decay (alpha, beta, and gamma) and know how the nucleus changes in each type of decay.
11. e. Students know alpha, beta, and gamma radiation produce different amounts and kinds of damage in matter and have different penetrations.
11. f.* Students know how to calculate the amount of a radioactive substance remaining after an integral number of half-lives have passed.
11. g.* Students know protons and neutrons have substructures and consist of particles called quarks.
Nuclear Chemistryhas to do with an atoms nucleusplural of nucleus = nucleiWhats a nucleus? Lets reviewAn atoms nucleus contains almost all of an atoms mass, but takes up very little of its volume. Subatomic Particlesthe particles that make up an atomProtons high mass, positive charge. Found in nucleus.
Neutrons high mass, no charge. Found in nucleus.
Electrons low mass, negative charge. Found orbiting around nucleus. (abbreviated e ) Comparison of Masses
ElectronAn AtomSize of atomSize of nucleus2 protons = He = heliumBasic Electrical Charge Laws+ and : Attract(pull together)
and : Repel(push away)
+ and + : Repel(push away) Like charges repel and Opposites attractSo why dont the protons in the nucleus fly apart? nuclear forceelectrostatic forceis stronger over short distancesis stronger over long distancesKey11NaSodium22.99Atomic NumberNumber of ProtonsNumber of Electrons (when atom is neutrally charged)Property unique to each elementKeyAverage atomic mass*Weighted Average number of Protons and Neutrons (approximately)NaSodium22.9911IsotopesWhen atoms have the same number of protons, but different numbers of neutrons, they are called isotopes. Examples: Carbon-14 has 6 protons and 8 neutrons.Carbon-12 has 6 protons and 6 neutrons.
Carbon-14 is found more often in living organisms than in non-living matter. It also undergoes radioactive decay which is why it is used for fossil dating.
IsotopesMore Examples: Uranium-238 has 92 protons and 146 neutrons.Uranium-235 has 92 protons and 143 neutrons.
Uranium-235 is more rare in nature than Uranium-238, but it also undergoes nuclear chain reactions more easily, which is why small amounts of Uranium-235 are used in nuclear weapons and nuclear power plants.
Some isotopes are more stable than others. Which isotope is more abundant?Neon-20Neon-22How many neutrons in each? Neon-20Neon-22
22 10 = 12 neutrons20 10 = 10 neutrons
Which isotope is more abundant?Bromine-79Bromine-80How many neutrons in each? Bromine-79Bromine-80
Lead has two isotopes with the following relative amounts: 80% Lead-207 20% Lead-208What would the average atomic mass calculate to be? 0.8(207) + 0.2(208) =207.2
Chlorine has two stable isotopes:Chlorine-35Chlorine-37What are the relative abundances (in %) of each isotope? x(35) + (1-x)(37) = 35.4535x 37x + 37 = 35.45-2x + 37 = 35.45 -2x = -1.55-2x = -1.55x = 0.775??%100 ??% 37 37 -2 -2x1 x
Chlorine has two stable isotopes:Chlorine-35Chlorine-37What are the relative abundances (in %) of each isotope? x(35) + (1-x)(37) = 35.4535x 37x + 37 = 35.45-2x + 37 = 35.45 -2x = -1.55-2x = -1.55x = 0.77577.5%22.5% 37 37 -2 -20.7750.225
So why dont the protons in the nucleus fly apart? nuclear forceelectrostatic forceis stronger over short distancesis stronger over long distances
Sometimes these forces are overcome. Fission a nucleus breaks apart.(ex. atomic bomb, nuclear power plants, radioactive decay)Fusion a nucleus merges with another.(ex. the sun, hydrogen bomb, experimental fusion reactors)
Both fission and fusion release radiation. It is called radiation because it radiates out.Common Types of Radiation (alpha): helium nucleus at high speed. (beta): electron at high speed.
(gamma): high energy photon.
He42e0-100harder to blockSymbolOther Types of Radiationneutron at high speed. Proton (or hydrogen nucleus) at high speed.
+ positron at high speed (the anti-matter version of an electron).
Na2311Na2211atomic massnumber of protonsWe can use conservation of mass and charge to figure out nuclear reactions just like chemical reactions. e0-1Th23490+He42U23892+??????We can use conservation of mass and charge to figure out nuclear reactions just like chemical reactions. e0-1Th23490+He42U23892+???Th23490We can use conservation of mass and charge to figure out nuclear reactions just like chemical reactions. e0-1Th23490+He42U23892+Th23490Pa23491
Half-LifeHalf-life how much time has passed when half of the original amount remains. How much of the original remains after two half-lives? How much after three half-lives?
How much after four half-lives?
or 50 %12 or 25 %14 or 12.5 %18 or 6.25 % 116 Table of Half-LivesIsotope NameSymbolHalf-LifeUranium-23823892U4.51 109 yearsUranium-23523592U7.1 108 yearsCarbon-14146C5,730 yearsStrontium-909038Sr28 yearsCobalt-606027Co5.27 yearsTable of Half-LivesIsotope NameSymbolHalf-LifeThorium-23423490Th24.1 daysProtactinium-23423491Pa6.75 hoursPolonium-21821884Po3.08 minutesRadon-21921986Rn4.00 secondsPolonium-21421484Po1.6 10-4 secondsAs a archaeologist you find a dead rat that contains 0.0009 grams of Carbon-14. A rat that died a year ago has 0.01 grams of Carbon-14. How long ago did the rat die? t = 5,730 years0.0009 g0.01 g= 111.112 116 132 16414181 H.L.2 H.L.3 H.L.4 H.L.5 H.L.6 H.L.As a archaeologist you find a dead rat that contains 0.0009 grams of Carbon-14. A rat that died a year ago has 0.01 grams of Carbon-14. How long ago did the rat die? t = 5,730 years 111.1 116183 H.L.4 H.L.3(5,730) = 4(5,730) =17,190 years 22,920 years 17,190 22,920 years ago Strontium-90 is one of the fallout products from atmospheric testing of nuclear weapons. If there were 50,000 grams of Strontium-90 in the U.S. southwest region when the 1963 testing ban began, how much Strontium-90 currently remains? t = 28 years2013 1963 =12 116 132 16414181 H.L.2 H.L.3 H.L.4 H.L.5 H.L.6 H.L.50 years50 yr28 yr=1.8 half-livesRadioactive Decay FormulasA = A0 e-( )tln (2) t12t =A0 A ln (2)ln ( )t3t =A0 Aln ( ) ln (2)tA0 = original amountA = current amountt = current timet = half-lifeEnergy-Mass EquivalenceSometimes in nuclear change a small amount of the mass disappears. It has been converted to a large amount of energy according to the formula: E = mc2speed of light: c = 3 108 m/senergy = (mass) (speed of light)2J = kg (m/s)2
Fission Nuclear Reaction
4 e in valence shell
Which isotope is more abundant?Lead-207Lead-208How many neutrons in each? Lead-207Lead-208