4Atomic Theory Atoms are the smallest particles of elements. Atoms were first proposed by Democritus over 2000 years ago.The idea of atoms was reintroduced in 1803 by John Dalton.
5Dalton’s Atomic Theory Atoms are tiny, discrete particlesAtoms are indestructibleAtoms of the same element have the same mass and propertiesAtoms combine in simple whole-number ratiosAtoms in different ratios produce different compounds.
6Dalton’s Atomic Theory Atoms are tiny, discrete particlesAtoms are indestructibleAtoms of the same element have the same mass and propertiesAtoms combine in simple whole-number ratiosAtoms in different ratios produce different compounds.We know that parts of Dalton’s atomic theory are no longer valid in today’s modern Quantum Mechanical model of the atom.
7Dalton’s Atomic Theory Atoms are tiny, discrete particlesAtoms are indestructibleAtoms of the same element have the same mass and propertiesWe know that atoms are made up of smaller particles, and that there are slight differences between atoms of the same element - isotopes.
8William CrookesUsed spectroscopy to discover thallium and used vacuums to measure its mass.Invented the radiometer.Improved vacuum systems.Used by Edison to make light bulbs.
9William Crookes What we now call the cathode ray tube. The Crookes’ Tube
10William CrookesUsed the cathode ray tube to to study electric fields in a vacuum and discovered rays, …which were called “cathode rays” by Goldstein,since they came from the cathode, or negative electrode.
11William CrookesThe shadow of the Maltese cross indicates that cathode rays travel in straight lines and can be stopped by a solid object.
12William CrookesHe found that the cathode rays could be deflected by a magnet.This suggested that the cathode rays might be a stream of electrically charged particles.
13Cathode Ray Tube + Cathode Anode Direction of cathode rays High voltage
14Cathode Ray Tube + Cathode Anode Direction of cathode rays Magnet High voltage
15to discover the electron. Cathode Ray TubeUsed by J. J. Thomson …to discover the electron.CathodeAnode+High voltage
16J.J. Thomson and Cathode Rays Attracted to positive electrodeThought might be atomsHad same charge to mass ratio regardless of metal in the cathodeThe particle was much less massive than the lightest element – HParticle must be common to all matter, a subatomic particle
17J.J. Thomson and Cathode Rays In 1897 J. J. Thomson found that cathode rays are a basic building block of matter.He had discovered the electron.
18J.J. Thomson and Cathode Rays The term “electron” comes from George Stoney’s term for the “minimum electrical charge”.Thomson concluded that this particle was the carrier of the minimum electrical charge and so the particle was later called an “electron”.
19J.J. Thomson and Cathode Rays Even though Crookes and others observed cathode rays, Thomson is credited with the discovery of the electron because he recognized that it was a fundamental particle of nature as well as a sub-atomic particle.
20J.J. Thomson and Cathode Rays Measured the charge to mass ratio, and found …… that if this “minimum charge” was equal to the charge on a hydrogen ion, then the mass of the electron would be 1/1837th the mass of a hydrogen atom.
21J.J. Thomson and Cathode Rays If that were the case, then the electron would be much smaller than the smallest atom ..…showing for the first time that matter is made up of particles smaller than atoms.Thomson tried to measure the fundamental charge on the electron.
22Robert A. MillikanRobert A. Millikan, an American physicist, set out to determine the charge on an electron.From 1909 through 1910, he performed what is now called the “Oil Drop Experiment”.
23Robert A. MillikanAtomizerHighVoltageTelescopeCast iron pot
24Robert A. Millikan Atomizer Parallel charged plates High Oil Drop VoltageOil DropTelescopeCast iron pot
25Robert A. MillikanRadiation stripped electrons from the oil droplets. The charged droplets fell between two electrically charged plates. By adjusting the voltage, he could change the rate of fall or rise of a single oil drop. After observing hundreds of drops, he calculated the charge on a single electron.
26Charges on drops are multiples of Robert A. MillikanCharges on drops are multiples of1.602 x coulombs.
27Robert A. Millikan 9.109 x 10-28 gram The fundamental charge on an electron is x coulombs.With J. J. Thomson’s charge to mass ratio, and Millikan’s charge on the electron, we are able to compute the mass of an electron:9.109 x gram
28Ernest RutherfordHe is to the atom what Darwin is to evolution, Newton to mechanics, Faraday to electricity and Einstein to relativity.John Campbell
29Ernest RutherfordHe moved from New Zealand to Cambridge University in England (1895) where he pioneered the detection of electromagnetic waves, but was lured away by J.J. Thomson on work that would lead to the discovery of the electron. The invention of radio communications went to Marconi, instead. He later switched to working with radioactivity (1896) and discovered alpha and beta rays. He went to Montreal to teach at McGill University (1898) where he continued his work on radioactivity with Frederick Soddy, and others ( ). He moved back to back to England to teach at Manchester (1907). He received the Nobel prize in chemistry in 1908 for his work on radioactivity in Canada.
30Ernest RutherfordIn 1907, he and a student, Hans Geiger, developed what would later become the “Geiger counter”. While at McGill, Rutherford discovered that after alpha rays passed through a thin film of mica, the image formed on a photographic plate was “fuzzy”. He and Geiger began a project to investigate the scattering of alpha particles by thin films. Rutherford later gave Ernest Marsden, an undergraduate, his own research project which was to look for evidence of the backscatter of alphas (1909). To their surprise, Marsden found that some alpha particles were scattered backwards from thin films of lead, platinum, tin, silver, copper, iron, aluminum, and gold.
31Ernest RutherfordRutherford remarked that it was like firing a navel gun at a piece of tissue paper and the shell bouncing back and hitting you. By 1910, Hans Geiger had finished his research on the forward scattering of alpha particles but he could not reconcile it with Marsden’s observations of the backscatter of alphas. The problem was passed on to Rutherford, who came up with the answer, and the astounding results were published in 1911.
32Ernest RutherfordRutherford had discovered a new piece to the atomic puzzle, the nucleus. According to Rutherford, the positively charged alpha particles were encountering a tiny, positively charged particle within the atoms of the metal and were being repelled. The atoms themselves appeared to mostly empty space. It was the repulsion of two positively charged particles which caused the scattering observed by Geiger and Marsden. Rutherford had found that atoms are mostly empty space with a small, dense, positively charged nucleus.
33Alpha scattering Apparatus for investigating alpha scattering. What some textbook authors call the “gold foil experiment.”
34+ Alpha scattering a source Most of the alpha particles pass through undeflected.
35+ Alpha scattering a source Some positive alpha particles are repelled by the small, dense, positively charged nucleus.+
36+ Alpha scattering a source Some positive alpha particles are repelled by the small, dense, positively charged nucleus.+
37Alpha scatteringAlpha particles are repelled by a small, dense, positively charged nucleus.Almost all the mass of an atom is in the nucleus. Atoms are mostly empty space.Electrons are located outside the nucleus.Published results in 1911.
38Ernest Rutherford N + a O + H Rutherford, during the First World War, worked on developing SONAR and submarine detection, but still found time to tinker with alpha radiation. In 1917 he bombarded nitrogen gas with alpha particles and discovered that oxygen and hydrogen were produced. Rutherford had resorted to alchemy and accomplished the first transmutation of one element into another. He had also indirectly discovered the proton.N + a O + H
39Ernest Rutherford N + a O + H We now know… 7 protons 1 proton
40Ernest RutherfordRutherford concluded that the nucleus must contain the positively charged protons in a number equal to the negative charge from the electrons, but this did not account for all of the mass of the atom. He, along with James Chadwick, rejected the idea that there must be additional protons and electrons in the nucleus, and concluded that there must be a neutral particle in the nucleus that accounted for the additional mass. In 1932, Chadwick confirmed the existence of the neutron.
42Demonstrations with radioactivity Investigate the properties ofAlpha, Beta and GammaRadiation
43Geiger-Mueller Tube Counter Wire (+ side of circuit) 2435Wire (+ side of circuit)Metal shield (- side)Low pressure Ar gasMica window (fragile)
44Geiger-Mueller Tube Rays leave the source Some hit the GM tube Most do nothingOne ray may cause a discharge…Sourceand the detector clicks
45Geiger-Mueller Tube Filled with low pressure argon gas About 1% efficiencyAbout 1 in 100 rays causes an electric spark between the case and the wireEach spark registers as a count or click on the counter
46Radioactivity a helium nuclei b electrons g Alpha particlesBeta particlesGamma raysabghelium nucleielectronshigh energy electromagnetic energy - similar to light, but higher in energy.
47Radioactivity Alpha particles An unstable nucleus splits to form a more stable nucleus an an alpha particle.An alpha particle is the nucleus of a helium atom.Two protons and two neutrons.Has a +2 charge.
48Radioactivity Beta particles Ejected from the nucleus when a neutron decays.A beta particle is identical to an electronHas a -1 charge.
49Radioactivity Gamma rays Emitted by an unstable nucleus as it becomes more stableElectromagnetic energy with short wavelengths and high energy.Has no charge.
50Radioactivity - comes from the natural decay of unstable atoms. - can be detected by photographic film, scintillation detector or a Geiger counter.- is “ionizing radiation”. Causes cell damage and mutations – cancer.- is protected against by shielding and distance.
51E Mass number /Atomic number A Z Mass number protons + neutronsProtons in nucleusEAMass numberZSymbol of ElementAtomic number
52U Mass number /Atomic number 235 92 Mass number protons + neutronsProtons in nucleusU235Mass number92Symbol of ElementAtomic number
53RadioactivityAlpha (a) particles are the nuclei of helium atoms and have the symbol 2He4.What is the atomic number of an a particle?2 He4
54RadioactivityAlpha (a) particles are the nuclei of helium atoms and have the symbol 2He4.What is the mass number of an a particle?2 He4
55RadioactivityAlpha (a) particles are the nuclei of helium atoms and have the symbol 2He4.4How many times heavier is an alpha particle than a hydrogen atom?
56RadioactivityBeta (b) particles are high speed electrons ejected from the nuclei of atoms and have the symbol -1e0.What is the mass number of a b particle?-1e0
57RadioactivityBeta (b) particles are high speed electrons ejected from the nuclei of atoms and have the symbol -1e0.No protons or neutrons in an electron.-1e0
58RadioactivityBeta (b) particles are high speed electrons ejected from the nuclei of atoms and have the symbol -1e0.What is the difference between a b particle and a “regular” electron?None
59Radioactivity Location Beta (b) particles are high speed electrons ejected from the nuclei of atoms and have the symbol -1e0.What is the difference between a b particle and a “regular” electron?Location
60RadioactivityGamma (g) rays are high energy electromagnetic waves, not particles.No protons, neutrons or electrons.Gamma rays have short wavelengths, high energies and travel at the speed of light.
61Gamma rays have short wavelengths Increasing energy… and high energies.
62What is the effect of an electric field on a, b, g ? Alpha, Beta, GammaElectric field from electrically charged platesWhat is the effect of an electric field on a, b, g ?Radioactive Source
63Alpha, Beta, Gamma b g a - - - - - - - - - Radioactive Source Electric field from electrically charged platesbgaRadioactive Source
64Alpha, Beta, Gamma b Are a, b and g rays deflected by magnetic fields? Electric field from electrically charged platesbAre a, b and g rays deflected by magnetic fields?gaRadioactive Source
68Radiation ProjectCreate a table listing information for each of the three kinds of radiation:Alpha, beta and gamma
69Properties to include in your table: Greek lettersymbolactually isatomic numbermass numberrelative massrelative. chargepenetrating abilityshielding
70Stop! Complete the chart on notebook paper, then continue. Nuclear Properties TablePropertyAlphaBetaGammaGreek LetterSymbolActually is…Atomic numberMass numberRelative massRelative chargePenetratingShieldingStop!Complete the chart on notebook paper, then continue.
80Nuclear Properties Table PropertyAlphaBetaGammaGreek LetterabgSymbol2He4-1e0NAActually is…He nucleuselectronEM energyAtomic number2-1Mass number4Relative mass1/1837Relative charge+2PenetratingLowMediumHighShielding2.5 cm of air;anything elseMetal, plastic or woodLead or concrete
81Protection from radiation Shielding 2. DistanceHow do you protect yourself from …AlphaBetaGamma2.5 cm of air, paper, skinaluminum, lead, other metals, wood, plastic, etc.up to a foot or two of lead, many feet of concrete
82There are some kinds of radiation you can not protect your self from.
83Radiation Gamma rays and high energy cosmic particles from space. But there is one kind of radiation hazard that you can protect against.
84That hazard comes from the uranium beneath your feet. Uranium in the ground decays according to …
85The uranium decay series Uranium-238 decays through many steps to make stable lead-206
86The uranium decay series Radon isthe only gas in the series.
87Hazards from radonSince radon is the only gas in the decay series of uranium ……it can work its way up through the ground and into your basements and crawl spaces.You breathe radon into your lungs.
88Hazards from radon And when radon is in your lungs… …it can decay and release an alpha particle ……which travels only a short distance before it is absorbed by your lungs, and transfers its energy.
89Hazards from radonThis ionizing radiation in your lungs can cause lung cancer.Smoking cigarettes and breathing radon really increases your chances of getting lung cancer.
90Protecting against radon Get a test kit to see if there is a problem. Charcoal canisters, which are sent off for analysis.Abatement:Seal places where gas gets in.Ventilation – bring in fresh air.
91Atomic Theory We know that atoms are mostly empty space. We know that atoms are made up of protons, neutrons and electrons.Protons and neutrons are located in a small, dense, positively charged nucleus.
92Atomic TheoryWe know atoms are mostly empty space and that protons and neutrons are located in a small, dense, positively charged nucleus because of Rutherford’s explanation of Geiger and Marsden’s work in alpha scattering (gold foil experiment ).
93Atomic TheoryWe know that electrons are outside the nucleus in an “electron cloud”.Electrons exist in specific energy levels, which explains the line spectra of the elements.Started with the Bohr model.
94Atomic Theory We now use the Quantum Mechanical Model of the atom. Quantum Theory describes the nature of electrons and their interactions with the electrons of other atoms in chemical reactions.
95Atomic TheoryThe subatomic particles that make up atoms have known properties like mass and electrical charge.Our understanding came through the efforts of a number of scientists like Thomson, Millikan, Rutherford, and Chadwick.
96U Mass number /Atomic number 235 92 Mass number protons + neutronsProtons in nucleusU235Mass number92Symbol of ElementAtomic number
97n H e Subatomic particles What do the numbers represent? proton 1protonelectronH1neutrone-1What do the numbers represent?
98Fill in the chart with the correct information. PropertyProtonNeutronElectronSymbolsLocationRel. massMass (amu)Mass (g)Rel. chargeCharge (C)Fill in the chart with the correct information.
99Proton Neutron Electron PropertyProtonNeutronElectronSymbolsp+ and 1H1n0 and 0n1e- and -1e0LocationRel. massMass (amu)Mass (g)Rel. chargeCharge (C)
100Proton Neutron Electron PropertyProtonNeutronElectronSymbolsp+ and 1H1n0 and 0n1e- and -1e0Locationnucleuscloud outside nucleusRel. massMass (amu)Mass (g)Rel. chargeCharge (C)
101Proton Neutron Electron PropertyProtonNeutronElectronSymbolsp+ and 1H1n0 and 0n1e- and -1e0Locationnucleuscloud outside nucleusRel. mass11/1837Mass (amu)Mass (g)Rel. chargeCharge (C)
102Proton Neutron Electron PropertyProtonNeutronElectronSymbolsp+ and 1H1n0 and 0n1e- and -1e0Locationnucleuscloud outside nucleusRel. mass11/1837Mass (amu)amuamuamuMass (g)Rel. chargeCharge (C)
103Proton Neutron Electron PropertyProtonNeutronElectronSymbolsp+ and 1H1n0 and 0n1e- and -1e0Locationnucleuscloud outside nucleusRel. mass11/1837Mass (amu)amuamuamuMass (g)1.673x10-241.675x10-249.11x10-29Rel. chargeCharge (C)
104Proton Neutron Electron PropertyProtonNeutronElectronSymbolsp+ and 1H1n0 and 0n1e- and -1e0Locationnucleuscloud outside nucleusRel. mass11/1837Mass (amu)amuamuamuMass (g)1.673x10-241.675x10-249.11x10-29Rel. charge+1-1Charge (C)
105Proton Neutron Electron PropertyProtonNeutronElectronSymbolsp+ and 1H1n0 and 0n1e- and -1e0Locationnucleuscloud outside nucleusRel. mass11/1837Mass (amu)amuamuamuMass (g)1.673x10-241.675x10-249.11x10-29Rel. charge+1-1Charge (C)+1.6x10-19 C-1.6x10-19 C
106Subatomic particles Protons and neutrons are located in the nucleus. Protons and neutrons have almost the same mass. Neutrons heavier.Electrons are outside the nucleus and much lighter than proton or neutron.Protons and electrons have the same charge but opposite polarity.Neutrons have no charge.
107Subatomic particlesProtons and neutrons are each made of smaller particles called quarks.Quarks are elementary particles just like electrons. They are not composed of smaller particles.There are six kinds of quarks:“up”, “down”, “top”, “bottom”, “charm” and “strange”.
108Subatomic particlesProtons are composed of two “up quarks” and one “down quark”.Neutrons are composed of two “down quarks” and one “up quark”.Quarks are held together to make protons and neutrons by the strong force, the strongest of the four fundamental forces in nature. Gravity, electromagnetism, weak and strong.
110Isotopes ……of the same element have the same number of protons and electrons but different numbers of neutrons.Therefore, isotopes of the same element have different masses.
111Isotopes … …don’t have to be radioactive. Some isotopes are unstable and decay, releasing alpha or beta particles, or gamma rays.But, there are many stable isotopes that don’t decay.
112Isotopes … …have different mass numbers but the same atomic number. Atomic number - the number of protons in the nucleus of an atom.Mass number - the sum of the protons and neutrons in the nucleus.
113E Symbols for Isotopes A is the symbol for mass number A Z Symbol of ElementEZAtomic numberZ is the symbol for atomic number
114U Symbols for Isotopes 235 92 An isotope of uranium Mass number Symbol of ElementU92Atomic numberAn isotope of uranium
115U Symbols for Isotopes An isotope of uranium Mass number 235 92 This form solves the word processor dilemma.U23592Symbol of ElementAtomic numberAn isotope of uranium
116U-235 Symbols for Isotopes Z = 92 How do you know the atomic number? Symbol of ElementFind U in the periodic table.Z = 92U-235Mass numberHow do you know the atomic number?
117Some elements have several Isotopes Lead has four naturally occurring isotopes, Pb-204, Pb-206, Pb-207, and Pb-208; but there are 23 man-made isotopes of lead.
118Some elements have several Isotopes Bismuth has only one naturally occurring isotope, Bi-209, but there are 22 man-made isotopes of bismuth.
119Finding the number of Protons, Neutrons, and Electrons The atomic number is the number of protons in the nucleus.The number of electrons in a neutral atom equals the number of protons.
120Finding the number of Protons, Neutrons, and Electrons The number of neutrons is the difference between the mass number and the atomic number.neutrons = A - Z
121Finding the number of Protons, Neutrons, and Electrons Look at the periodic table and find the element by using the symbol.Z = 92protons = 92electrons = 92A = 235protons + neutrons = 235
122Finding the number of Protons, Neutrons, and Electrons How many neutrons are in a U-235 atom?Z = 92protons = 92electrons = 92A = 235protons + neutrons = 235
123Finding the number of Protons, Neutrons, and Electrons How many neutrons are in a U-235 atom?Z = 92protons = 92electrons = 92235 – 92 = 143 neutrons
124Q. Find the number of neutrons in the Ba-137 isotope. Finding the number of Protons, Neutrons, and ElectronsQ. Find the number of neutrons in the Ba-137 isotope.In the Ba-137 isotope …… Z = 56 and A = 137137 – 56 = 81 neutrons
125Copy the following table on notebook paper, and fill in the blanks. Finding the number of Protons, Neutrons, and ElectronsCopy the following table on notebook paper, and fill in the blanks.
126Element Symbol Z A #p #n #e Zinc 66 In 68 85 38 82 210 Rn 136 35 47 Finding the number of Protons, Neutrons, and ElectronsElementSymbolZA#p#n#eZinc66In68853882210Rn1363547
127Complete the table, then go on. Finding the number of Protons, Neutrons, and ElectronsStop!Complete the table, then go on.ElementSymbolZA#p#n#eZinc66In68853882210Rn1363547
128Element Symbol Z A #p #n #e Zinc 66 In 68 85 38 82 210 Rn 136 35 47 Finding the number of Protons, Neutrons, and ElectronsElementSymbolZA#p#n#eZinc66In68853882210Rn1363547
129Element Symbol Z A #p #n #e Zinc Zn 30 66 36 In 68 85 38 82 210 Rn 136 Finding the number of Protons, Neutrons, and ElectronsElementSymbolZA#p#n#eZincZn306636In68853882210Rn1363547
130Element Symbol Z A #p #n #e Zinc Zn 30 66 36 Indium In 49 117 68 85 38 Finding the number of Protons, Neutrons, and ElectronsElementSymbolZA#p#n#eZincZn306636IndiumIn4911768853882210Rn1363547
131Element Symbol Z A #p #n #e Zinc Zn 30 66 36 Indium In 49 117 68 Finding the number of Protons, Neutrons, and ElectronsElementSymbolZA#p#n#eZincZn306636IndiumIn4911768StrontiumSr38854782210Rn13635
132Element Symbol Z A #p #n #e Zinc Zn 30 66 36 Indium In 49 117 68 Finding the number of Protons, Neutrons, and ElectronsElementSymbolZA#p#n#eZincZn306636IndiumIn4911768StrontiumSr388547LeadPb82210128Rn13635
133Element Symbol Z A #p #n #e Zinc Zn 30 66 36 Indium In 49 117 68 Finding the number of Protons, Neutrons, and ElectronsElementSymbolZA#p#n#eZincZn306636IndiumIn4911768StrontiumSr388547LeadPb82210128RadonRn8622213635
134Element Symbol Z A #p #n #e Zinc Zn 30 66 36 Indium In 49 117 68 Finding the number of Protons, Neutrons, and ElectronsElementSymbolZA#p#n#eZincZn306636IndiumIn4911768StrontiumSr388547LeadPb82210128RadonRn86222136BromineBr35
135Atomic mass is the weighted average of all the isotopes of an element Boron has two isotopes:B % amuB % amu0.198 x x =10.81 amu
136Atomic mass is the weighted average of all the isotopes of an element Determine the atomic mass of silicon:Si % amuSi % amuSi % amux x x =amu
137Atomic mass is the weighted average of all the isotopes of an element Consider the two isotopes of chlorine. Which isotope is more abundant?Cl - 35 ??.?? % amuCl - 37 ??.?? % amuThe average atomic mass is amu.
138Atomic mass is the weighted average of all the isotopes of an element Consider the two isotopes of chlorine. Which isotope is more abundant?Cl % amuCl % amuThe average atomic mass is amu.
139Atomic mass is the weighted average of all the isotopes of an element Which isotope of neon is more abundant? Ne-20 or Ne-22Ne-20 90%Ne-22 10%
140How are isotopes of the same element alike and different? Number of protons and electronsAtomic numberChemical propertiesDifferent:Number of neutronsMass NumberAtomic mass of the isotopes
141Which of the following is the same for the three isotopes of magnesium? The atomic number of 12The number of protons and electronsThe number of neutronsThe atomic weight of AMUThe reaction with hydrochloric acidThe speed of gaseous Mg atoms
142All three isotopes of magnesium have the same atomic number. Which of the following is the same for the three isotopes of magnesium?The atomic number of 12SameAll three isotopes of magnesium have the same atomic number.
143Which of the following is the same for the three isotopes of magnesium? 2. The number of protons and electronsSameAll isotopes of the same element have the same number of protons in the nucleus, and electrons outside the nucleus.
144Which of the following is the same for the three isotopes of magnesium? 3. The number of neutronsNot the sameThe number of neutrons varies with the isotope. Different isotopes have different numbers of neutrons.
145Not the same Mg-24 23.985 AMU Mg-25 24.986 AMU Mg-26 25.983 AMU Which of the following is the same for the three isotopes of magnesium?4. Atomic weight of AMUNot the sameMg-24 AMUMg-25 AMUMg-26 AMU
146All isotopes of the same element react the same chemically. Which of the following is the same for the three isotopes of magnesium?5. The reaction with HClSameAll isotopes of the same element react the same chemically.The number and arrangement of electrons is the same for each isotope.
147The speeds of atoms depend on mass. Which of the following is the same for the three isotopes of magnesium?6. The speed of gaseous Mg atomsNot the sameThe speeds of atoms depend on mass.Heavier atoms move more slowly, and lighter atoms move faster.
148How did knowing about Graham’s Law allow the United States to win World War II?
149Who were the two guys responsible for winning World War II? Fat Man, and …Little BoyAtomic bombs dropped on Hiroshima and Nagasaki
163Only one element has unique names for its isotopes … Deuterium and tritium are used in nuclear reactors and fusion research.
164Some isotopes are radioactive Radioactive isotopes are called radioisotopes.Radioisotopes can emit alpha, beta or gamma radiation as they decay.
165Man-made IsotopesMan-made isotopes are usually made by bombarding atoms with protons or neutrons.Cobalt-59 occurs naturally. When a neutron “sticks” to the nucleus, cobalt-60 is formed.
166Uses for IsotopesRadioisotopes are used to kill cancer cells. (Co-60, Bi-212)Radioisotopes are used in “imaging” living and nonliving systems.Radioisotopes are used as tracers in chemical reactions.
168What is half life?Half life is the time needed for one half of a radioisotope to decay.Suppose you start with grams of a radioisotope that has a half life of exactly 1 year.
169What is half life? How much will be left after 1 year? Suppose you start with grams of a radioisotope that has a half life of exactly 1 year.
170What is half life? After one year there will be 50.0 g left. After a second year there will be 25.0 g left.Suppose you start with grams of a radioisotope that has a half life of exactly 1 year.
171What is half life? After one year there will be 50.0 g left. After a second year there will be 25.0 g left.After a third year there will be 12.5 grams left.After a fourth year there will be 6.25 grams left.
172Half life project Pick a mass between 10g and 50g. Decide on a half life – any time.Scale your graph – mass on y-axis and at least six (6) half-lives on the x-axis.Plot the masses after intervals of one half-life.
173Half life project What shape is the graph? When will the mass of the radioisotope fall to zero?When is the radioactivity no longer a problem?What mathematical function describes radioactive decay?
176Half life project A = A0e-kt 10 Exponential decay 5 Activity (counts/min)2.5t1/2t1/2t1/2time
177Half life project10Radiation is “not a problem” when it falls below background level.5Activity (counts/min)background2.5t1/2t1/2t1/2time
178Half life project 400 years Questions: 1. A radioisotope has a half-life of 100 years. How long will it take for the radiation to decrease to 1/16 of its original value?400 years
179Half life project 4 hours Questions: 2. A radioisotope has an activity of 560 counts per minute. After 16 hours the count rate has dropped to 35 counts per minute. What is the half life of the radioisotope?4 hours
187Beta decay Beta decay occurs because of the instability of a neutron. Neutrons are a little more massive than protons; neutrons are neutral.What does this suggest about the composition of neutrons?
188Beta decayScientists used to think that neutrons might be a combination of a proton and an electron.We know that neutrons decay into protons, which stay in the nucleus, and electrons, which are ejected from the nucleus as beta particles.
189Beta decayThe conversion of a neutron to a proton involves the “weak” force. An “up” quark flips to become a “down” quark. When this occurs a high energy electron (beta) and an antineutrino are produced, both of which leave the nucleus.
190Beta decayDecay of a neutron:0n1 1H e0neutronprotonelectronThe electron ejected from the nucleus is a beta particle.
191Beta decayTechnically, the decay of a neutron also involves a neutrino.0n1 1H e n0neutronprotonelectronanti-neutrino
192Beta decay 0n1 1H1 + -1e0 + 0n0 Actually, an anti-neutrino. neutron The word “neutrino” comes from Enrico Fermi, meaning “little neutral one” in Italian.0n1 1H e n0neutronprotonelectronanti-neutrino
193Beta decayA neutrino is a particle with no charge and almost no mass.0n1 1H e n0neutronprotonelectronanti-neutrino
194Beta decayA neutrino carries off some of the energy in the decay of the neutron.0n1 1H e n0neutronprotonelectronanti-neutrino
195Beta decayWhen predicting the products of beta decay we will ignore neutrinos.0n1 1H e n0neutronprotonelectronanti-neutrino
196Beta decay Suddenly a neutron decays! Start with a Li atom with 3 protons and4 neutrons.Beta decaySuddenly aneutron decays!Now thereare 4 protons and 3 neutrons.A beta particle goes zipping out of the nucleus.
197Beta decay A neutron decays to make a proton. The number of neutrons The number of protonsThe mass numberThe atomic numberdecreases by 1increases by 1stays the same.
203Gamma raysGamma radiation is often emitted along with alpha and beta radiation.When a decay event occurs, “extra” energy is sometimes left in the nucleus.
204Gamma raysThe “extra” energy in the decay product is released as gamma radiation. This lowers the energy of the nucleus and makes it more stable.
205Review: decay equations Alpha:Go down two on periodic tableAtomic number decreases by 2Mass number decreases by 4Beta:Go up one on periodic tableAtomic number increases by 1Mass number stays the same
207Did you ever wonder ...Why the nucleus stays together with all those positively charged protons in such a small space?Protons have a positive charge and objects with like charges repel each other.
208Why do they look like this? Each hair has the same charge.
209Did you ever wonder ... Because of the electrostatic repulsion… …the nucleusshouldn’t even exist!
210Did you ever wonder ... The strong force. There must be a force that is stronger than the electrostatic repulsion.The strong force.
211Did you ever wonder ...The strong force is the force that holds the quarks together to make protons and neutrons.The residual strong force extends from the quarks in a proton or neutron to the quarks in an adjacent proton or neutron and holds the nucleus together.
213Here’s a mystery Consider the iron-56 isotope. It has a mass of amu.How many protons, neutrons and electrons?26 protons30 neutrons 26 electrons
214Here’s a mystery But! Protons: 26 x 1.0073 = 26.189 Calculate the mass of the Fe-56 atom in amu from the sum of the parts:Protons: 26 x =Neutrons: 30 x =Electrons: 26 x =Total mass =But!The actual mass is
215Here’s a mysteryThe actual mass of an isotope can be found using a device called a mass spectrometer.The actual mass is
216magnetic field Mass spectrometer magneticfieldMass spectrometer
217Magnetic field makes charged atoms curve. magneticfieldMagnetic field makes charged atoms curve.
218Here’s a mysteryThe sum of the protons, neutrons and electrons is amu.but,The actual mass is amu.– = amu
219Here’s a mystery– = amuSum of parts: p+, n, e-actual isotope mass?Where is the missing mass?
220Recall Einstein’s famous equation: The solutionRecall Einstein’s famous equation:E = mc2What does it tell us?Matter and energy are equivalent.
221The solution Matter can exist as energy and … … energy can exist as matter.They are both the same “thing”.All calculated from E = mc2
222The solutionThe difference between the mass of the parts (p+, n and e-) and the actual mass is called the “mass defect” and equals the mass of nuclear material that “exists as energy”.
223The solutionThe energy from the missing mass is the binding energy of the nucleus.The binding energy is derived from the strong force which does hold the nucleus together.
224The solutionThe binding energy is the energy required to “take apart” the nucleus to form nothing but individual protons and neutrons.
225Is this binding energy related to nuclear energy?
226Nuclear energyAll nuclear decay is accompanied by a release of energy.Alpha and beta particles have high kinetic energies.Gamma rays are electromagnetic energy.All have enough energy to ionize atoms.
227cancer Nuclear energy An ion is a “charged atom” or group of atoms. Ionization occurs when electrons are removed from atoms by a, b or g radiation.cancerThis can result in damage to your body.
228Nuclear energy Forms of ionizing radiation are: Alpha Beta Gamma X-raysCosmic raysNeutronsPositronsUltraviolet light (UV) can cause cancer, but it is not ionizing radiation.
229There’s even more!Some of the energy that holds the nucleus together is carried away by the alpha, beta and gamma radiation.But there is an even greater release of energy when the atom splits apart …
231Nuclear fissionFission – the splitting of an atom after the nucleus absorbs a neutron.
232Nuclear fission A neutron collides with a nucleus and is absorbed. The mass number of the atom increases and the nucleus becomes unstable.
233Nuclear fissionThe unstable nucleus splits into two or more fission fragments.Plus, two or three neutrons are released along with a great deal of energy.The neutrons strike other atoms causing more fission.
243Nuclear reactor Containment building Reactor core Fuel rods Heat exchangerSteam generatorSteam to turbineFuel rodsWater from cooling lakeWater circulates in the core
244Nuclear reactor Containment building Cadmium control rods – absorb neutronsReactor coreSteam to turbineFuel rodsWater from cooling lakeWater circulates in the core
245Nuclear reactor Containment building The water in the core serves two functions.(1) The water cools the core and carries away heat.(2) Water is a moderator. The water slows the neutrons so that they can cause fission. Fast neutrons do not cause fission.Nuclear reactorReactor coreSteam to turbineFuel rodsWater from cooling lakeWater circulates in the core
246Nuclear reactor Containment building Reactor core Fuel rods Water from cooling lakeWater circulates in the core
247Nuclear reactor Containment building Reactor core Fuel rods Heat exchangerSteam generatorFuel rodsWater from cooling lakeWater circulates in the core
248Nuclear reactor Containment building Reactor core Fuel rods Heat exchangerSteam generatorFuel rodsWater from cooling lakeWater circulates in the core
249Nuclear reactor Containment building Reactor core Fuel rods Heat exchangerSteam generatorSteam to turbineFuel rodsWater from cooling lakeWater circulates in the core
250From nuclear energy to… Heat exchangerSteam generatorTransmission wiresturbinegeneratorSteam to turbineCondensed steamWater from cooling lakeCooling towers or lake
251Electrical energy Heat exchanger Steam generator Transmission wires turbinegeneratorSteam to turbineCondensed steamWater from cooling lakeCooling towers or lake
252Electrical energyThis part of the system is the same regardless of how the steam is produced. The heat can come from nuclear energy or by burning coal, natural gas or fuel oil.Heat exchangerSteam generatorTransmission wiresturbinegeneratorSteam to turbineCondensed steamWater from cooling lakeCooling towers or lake
253Electrical energy In fact, the only purpose of a nuclear reactor is to boil water.
254Pros and consCheap, plentiful power, no CO2, nuclear waste, terrorist attack, running out of oil and coal, on-site storage, breeder reactors, transportation of spent fuel, “not in my backyard”, …