Chapter 10 Nuclear Chemistry Section 10.1 Radioactivity Section 10.4 Fission and Fusion

Chapter 10 Nuclear Chapter 10 Nuclear ChemistryChemistry

Section 10.1 RadioactivitySection 10.1 Radioactivity

Section 10.4 Fission and FusionSection 10.4 Fission and Fusion


Nuclear DecayNuclear Decay Antoine Henri Becqueral (1852-1908)-discovery Antoine Henri Becqueral (1852-1908)-discovery

of radioactivityof radioactivity Radioactivity-the process in which an unstable Radioactivity-the process in which an unstable

atomic nucleus emits charged particles and atomic nucleus emits charged particles and energyenergy

Any atom containing an unstable nucleus is a Any atom containing an unstable nucleus is a radioactive isotope aka. radioisotoperadioactive isotope aka. radioisotope


Nuclear DecayNuclear Decay Becquerel-used uranium-238 in his experimentBecquerel-used uranium-238 in his experiment Radioisotopes spontaneously change into other Radioisotopes spontaneously change into other

isotopes over time.isotopes over time. When composition of a radioisotope When composition of a radioisotope

changes=undergoes nuclear decaychanges=undergoes nuclear decay Key Concept: During nuclear decay, atoms of Key Concept: During nuclear decay, atoms of

one element can change into atoms of a one element can change into atoms of a different element altogether.different element altogether.

Section 10.1 Radioactivity Section 10.1 Radioactivity

Types of Nuclear RadiationTypes of Nuclear Radiation Radioactive substances can be detected by Radioactive substances can be detected by

measuring the nuclear radiation they give off.measuring the nuclear radiation they give off. Nuclear radiation-charged particles and energy Nuclear radiation-charged particles and energy

that are emitted from the nuclei of radioisotopesthat are emitted from the nuclei of radioisotopes Key Concept: Common types of nuclear Key Concept: Common types of nuclear

radiation include radiation include alpha particlesalpha particles, , beta particlesbeta particles, , and and gamma raysgamma rays..


Types of Nuclear Radiation: Alpha DecayTypes of Nuclear Radiation: Alpha Decay Uranium-238 decays=emits Uranium-238 decays=emits alpha particlesalpha particles Def.-a positively charged particle made up of two Def.-a positively charged particle made up of two

protons and two neutronsprotons and two neutrons ( (the same as a helium the same as a helium nucleusnucleus))

Symbol for alpha particle 4/2 He; subscript(2) is Symbol for alpha particle 4/2 He; subscript(2) is the atomic number; superscript(4) is the mass the atomic number; superscript(4) is the mass number (#protons + #neutrons)number (#protons + #neutrons)

Also notated by Greek letter Also notated by Greek letter αα


Types of Nuclear Radiation: Alpha DecayTypes of Nuclear Radiation: Alpha Decay Refers to nuclear decay that releases alpha particlesRefers to nuclear decay that releases alpha particles Is an example of a nuclear reactionIs an example of a nuclear reaction Nuclear reactions can be expressed as equations.Nuclear reactions can be expressed as equations. 238/92 U 238/92 U → → 234/90 Th + 4/2 He234/90 Th + 4/2 He Alpha decay: Alpha decay: product isotope has two fewer protons and product isotope has two fewer protons and

two fewer neutrons than the reactant isotopetwo fewer neutrons than the reactant isotope Alpha particles: Alpha particles: least penetrating and only travel a few least penetrating and only travel a few

centimeters in the aircentimeters in the air


Types of Nuclear Radiation: Beta DecayTypes of Nuclear Radiation: Beta Decay Thorium-234 decays=releases negatively Thorium-234 decays=releases negatively

charged radiationcharged radiation ( (beta particlesbeta particles)) Def.-an electron emitted by an unstable nucleusDef.-an electron emitted by an unstable nucleus Nuclear equations written: 0/-1 e or Nuclear equations written: 0/-1 e or ββ Atomic number is -1 because of negative chargeAtomic number is -1 because of negative charge Very little mass (1/1836)=mass number is 0Very little mass (1/1836)=mass number is 0

Section 10.1 RadioactivitySection 10.1 Radioactivity Types of Nuclear Radiation: Beta DecayTypes of Nuclear Radiation: Beta Decay

How can an atom’s nucleus, which is positively charged, How can an atom’s nucleus, which is positively charged, emit a negatively charged particle?emit a negatively charged particle?

A neutron decomposes into a proton and an electron.A neutron decomposes into a proton and an electron. The proton stays trapped in the nucleus; the electron is The proton stays trapped in the nucleus; the electron is

releasedreleased 234/90 Th 234/90 Th →→ 234/91 Pa + 0/-1 e 234/91 Pa + 0/-1 e The product isotope has 1 proton more and 1 neutron The product isotope has 1 proton more and 1 neutron

fewer than the reactant isotope.fewer than the reactant isotope. Mass numbers of isotopes are the same b/c the beta Mass numbers of isotopes are the same b/c the beta

particle emitted basically has no mass.particle emitted basically has no mass. Beta particles: smaller mass, move at faster speed and Beta particles: smaller mass, move at faster speed and

penetrate more than alpha particlespenetrate more than alpha particles


Types of Nuclear Radiation: Gamma DecayTypes of Nuclear Radiation: Gamma Decay Nuclear radiation does not always consist of Nuclear radiation does not always consist of

charged particlescharged particles.. Gamma ray-a penetrating ray of energy emitted Gamma ray-a penetrating ray of energy emitted

by an unstable nucleusby an unstable nucleus Gamma radiation: has no charge and no massGamma radiation: has no charge and no mass ****Travel through space at the speed of lightTravel through space at the speed of light


Types of Nuclear Radiation: Gamma DecayTypes of Nuclear Radiation: Gamma Decay Gamma Decay: the atomic number and mass Gamma Decay: the atomic number and mass

number of the atom number of the atom remain the sameremain the same ****The energy of the nucleus decreasesThe energy of the nucleus decreases Often accompanies alpha or beta decay.Often accompanies alpha or beta decay. Abbreviated: Abbreviated: γγ Much more penetrating than alpha or beta Much more penetrating than alpha or beta

particlesparticles Takes several centimeters of lead or meters of Takes several centimeters of lead or meters of

concrete to stop gamma radiationconcrete to stop gamma radiation

Penetrating Powers of Nuclear RadiationPenetrating Powers of Nuclear RadiationFigure 4

Section 10.1


Effects of Nuclear RadiationEffects of Nuclear Radiation We are exposed to nuclear radiation daily.We are exposed to nuclear radiation daily. Background radiation-nuclear radiation that Background radiation-nuclear radiation that

occurs naturally in the environmentoccurs naturally in the environment Radioisotopes in air, water, rocks, plants and Radioisotopes in air, water, rocks, plants and

animals contribute to background radiation.animals contribute to background radiation. Cosmic rays (streams of charged particles) from Cosmic rays (streams of charged particles) from

outer spaceouter space Background radiation levels, in general, are low Background radiation levels, in general, are low

enough to be safe.enough to be safe.


Effects of Nuclear RadiationEffects of Nuclear Radiation Nuclear radiation goes over background Nuclear radiation goes over background

levels=damage cells and tissues of the bodylevels=damage cells and tissues of the body Key Concept: Nuclear radiation can ionize Key Concept: Nuclear radiation can ionize

atoms.atoms. Cells exposed=bonds holding DNA molecules Cells exposed=bonds holding DNA molecules

and proteins together may break=cells may not and proteins together may break=cells may not function properlyfunction properly

Alpha particles, Beta particles and Gamma rays Alpha particles, Beta particles and Gamma rays are all forms of ionizing radiation.are all forms of ionizing radiation.


Effects of Nuclear RadiationEffects of Nuclear Radiation Alpha particles-skin damage similar to a burn; Alpha particles-skin damage similar to a burn;

not serious hazard unless the substance not serious hazard unless the substance emitting the particles is inhaled or eatenemitting the particles is inhaled or eaten

Beta particles-damages tissues in the body more Beta particles-damages tissues in the body more than alpha particlesthan alpha particles

Gamma rays-can penetrate deeply into the Gamma rays-can penetrate deeply into the human body; all organs can be exposed to human body; all organs can be exposed to ionization damageionization damage


Detecting Nuclear RadiationDetecting Nuclear Radiation Scientific instruments can measure nuclear radiation.Scientific instruments can measure nuclear radiation. Key Concept: Devices that are used to detect nuclear Key Concept: Devices that are used to detect nuclear

radiation include radiation include Geiger counters and film badgesGeiger counters and film badges.. Geiger counter-uses gas-filled tube to measure ionizing Geiger counter-uses gas-filled tube to measure ionizing

radiationradiation Nuclear radiation enter the tube, ionizes atoms of the Nuclear radiation enter the tube, ionizes atoms of the

gas, ions produce an electric current (measured)gas, ions produce an electric current (measured) >the amount of nuclear radiation, the >the electric >the amount of nuclear radiation, the >the electric

current produced in the tubecurrent produced in the tube


Detecting Nuclear RadiationDetecting Nuclear Radiation People working near or with radioactive People working near or with radioactive

materials wear film badges to monitor their materials wear film badges to monitor their exposure to nuclear radiation.exposure to nuclear radiation.

Film badge-piece of photographic film wrapped Film badge-piece of photographic film wrapped in paperin paper

Film is developed and replaced with a new one Film is developed and replaced with a new one periodicallyperiodically

Exposure on film shows the amount of radiation Exposure on film shows the amount of radiation the person wearing badge was exposed to the person wearing badge was exposed to


Alternative energy sources may eventually take Alternative energy sources may eventually take the place of fossil fuels (oil and coal)the place of fossil fuels (oil and coal)

Nuclear energy is one that is widely used today.Nuclear energy is one that is widely used today. After discovery of radioactivity, found that atomic After discovery of radioactivity, found that atomic

nuclei have vast amounts of energynuclei have vast amounts of energy Transmutations involved more than just the Transmutations involved more than just the

conversion of one element into another; they conversion of one element into another; they also involved conversion of mass into energyalso involved conversion of mass into energy..

Transmutation-conversion of atoms of one Transmutation-conversion of atoms of one element to atoms of another (Section 10.3)element to atoms of another (Section 10.3)


Nuclear ForcesNuclear Forces What holds the nucleus of an atom together?What holds the nucleus of an atom together? Strong nuclear force-the attractive force that bind Strong nuclear force-the attractive force that bind

protons and neutrons together in the nucleusprotons and neutrons together in the nucleus Does not depend on charge: acts among protons, Does not depend on charge: acts among protons,

among neutrons, and both protons and neutronsamong neutrons, and both protons and neutrons Key Concept: Over very short distances, the strong Key Concept: Over very short distances, the strong

nuclear force is much greater than the electric forces nuclear force is much greater than the electric forces among protons.among protons.

Weakens as protons and neutrons get farther apart.Weakens as protons and neutrons get farther apart.


The Effect of Size on Nuclear ForceThe Effect of Size on Nuclear Force Effect of size of the nucleus on the force is complicated.Effect of size of the nucleus on the force is complicated. More protons and neutrons=more possibilities there are More protons and neutrons=more possibilities there are

for strong nuclear force attractionsfor strong nuclear force attractions As size of nucleus increases, distance between protons As size of nucleus increases, distance between protons

and neutrons increasesand neutrons increases **Strong nuclear forces act over short **Strong nuclear forces act over short

distances=possibilities of many attractions is not realized distances=possibilities of many attractions is not realized in a large nucleusin a large nucleus

Nuclear force felt by proton and neutron in a large Nuclear force felt by proton and neutron in a large nucleus is about the same as the force felt in a small nucleus is about the same as the force felt in a small nucleusnucleus


Unstable NucleiUnstable Nuclei Nucleus becomes unstable (ie. Radioactive) Nucleus becomes unstable (ie. Radioactive)

when the strong nuclear force can no longer when the strong nuclear force can no longer overcome the repulsive electric forces among overcome the repulsive electric forces among protonsprotons

Electric forces increase as nucleus size Electric forces increase as nucleus size increases.increases.


FissionFission Hahn and Strassman (German chemists) 1938Hahn and Strassman (German chemists) 1938 Series of transmutation experiments (conversion Series of transmutation experiments (conversion

of atoms of one element to atoms of another of atoms of one element to atoms of another element)element)

Bombarded uranium-235 with high-energy Bombarded uranium-235 with high-energy neutrons (produce more massive elements)neutrons (produce more massive elements)

Instead, Instead, produced isotopes of Bariumproduced isotopes of Barium Lise Meitner and Otto Frisch (1939) explained Lise Meitner and Otto Frisch (1939) explained

the results of the experimentsthe results of the experiments


FissionFission Uranium-235 nuclei broken into smaller Uranium-235 nuclei broken into smaller

fragments (nuclear fission)fragments (nuclear fission) Def.-the splitting of an atomic nucleus into two Def.-the splitting of an atomic nucleus into two

smaller partssmaller parts Krypton-91, Barium-142, and Krypton-91, Barium-142, and EnergyEnergy Key Concept: In nuclear fission, tremendous Key Concept: In nuclear fission, tremendous

amount of energy can be produced from very amount of energy can be produced from very small amounts of mass.small amounts of mass.

Nuclear Fission Nuclear Fission of Uranium-235of Uranium-235

Figure 18


Converting Mass Into EnergyConverting Mass Into Energy When fission occurs, some of the mass of the When fission occurs, some of the mass of the

reactants is lost.reactants is lost. Lost mass is converted into energy.Lost mass is converted into energy. **Einstein (30 years before fission) introduced **Einstein (30 years before fission) introduced

the mass energy equation: the mass energy equation: E=mcE=mc22

Equation described how mass and energy relateEquation described how mass and energy relate E=energy; m=mass; c=speed of light (3.0 x 10E=energy; m=mass; c=speed of light (3.0 x 1088

m/s) m/s)


Converting Mass Into EnergyConverting Mass Into Energy Small amount of mass = release an enormous Small amount of mass = release an enormous

amount of energyamount of energy Large amount of energy = small amount of massLarge amount of energy = small amount of mass Law of conservation of mass and energy-the Law of conservation of mass and energy-the

total amount of mass and energy remains total amount of mass and energy remains constantconstant


Triggering a Chain ReactionTriggering a Chain Reaction Nuclear fission can follow a pattern where one Nuclear fission can follow a pattern where one

reaction leads to a series of others.reaction leads to a series of others. Def.-neutrons released during the splitting of an Def.-neutrons released during the splitting of an

initial nucleus trigger a series of nuclear fissions.initial nucleus trigger a series of nuclear fissions. Speed of chain reactions can vary.Speed of chain reactions can vary. Uncontrolled-all of the released neutrons are Uncontrolled-all of the released neutrons are

free to cause other fissions (free to cause other fissions (fast and intense fast and intense release of energyrelease of energy) Ex. Nuclear weapons) Ex. Nuclear weapons


Triggering a Chain ReactionTriggering a Chain Reaction Controlled-some neutrons absorbed by nonfissionable Controlled-some neutrons absorbed by nonfissionable

materials (1 new fission for each splitting of an atom)materials (1 new fission for each splitting of an atom) Heat-used to generate electrical energyHeat-used to generate electrical energy Disadvantage-radioactive wasteDisadvantage-radioactive waste Sustain a chain reaction: Sustain a chain reaction: each nucleus that’s split must each nucleus that’s split must

produce one neutron that causes the fission of another produce one neutron that causes the fission of another nucleusnucleus

Critical mass-smallest possible mass of a fissionable Critical mass-smallest possible mass of a fissionable material that can sustain a chain reactionmaterial that can sustain a chain reaction

Chain Reaction Chain Reaction of Uranium-235of Uranium-235

Figure 19


Figure 19


Figure 19


Figure 19


Figure 19

Chain Chain Reaction of Reaction of

Uranium-235Uranium-235

Figure 19



Figure 19



Figure 19



Figure 19


Nuclear Energy from FissionNuclear Energy from Fission Nuclear power plants-20% of electricity in U.S.Nuclear power plants-20% of electricity in U.S. Controlled fission of uranium-235; done in vessel (fission Controlled fission of uranium-235; done in vessel (fission

reactor)reactor) Nuclear power plants: no air pollutantsNuclear power plants: no air pollutants Safety and environmental issues: Safety and environmental issues: employee protectionemployee protection, ,

radioactive waste (isolated and stored),radioactive waste (isolated and stored), lose control of lose control of fission reactor (core melts b/c cooling system fails fission reactor (core melts b/c cooling system fails {meltdown}); radioactive material may be released{meltdown}); radioactive material may be released, , structure housing reactor is not secure=environment can structure housing reactor is not secure=environment can be contaminatedbe contaminated


FusionFusion Also releases huge amounts of energyAlso releases huge amounts of energy Def.-a process in which the nuclei of two atoms Def.-a process in which the nuclei of two atoms

combine to form a larger nucleuscombine to form a larger nucleus Same as fission: Same as fission: a small fraction of the reactant a small fraction of the reactant

mass is converted into energymass is converted into energy Sun and stars powered by fusion of H and HeSun and stars powered by fusion of H and He Sun : Sun : 600 million tons of H undergo fusion each 600 million tons of H undergo fusion each

second; 4 million tons of it is converted to energysecond; 4 million tons of it is converted to energy


FusionFusion Require extremely high temperaturesRequire extremely high temperatures Sun: temps. can reach 10,000,000 C (matter Sun: temps. can reach 10,000,000 C (matter

exists as plasma)exists as plasma) Plasma-a state of matter in which atoms have Plasma-a state of matter in which atoms have

been stripped of their electronsbeen stripped of their electrons Gas (nuclei and electrons)Gas (nuclei and electrons) Future: may provide an efficient and clean Future: may provide an efficient and clean

source of electricitysource of electricity


FusionFusion Plan: fusion reactors fueled by 2 hydrogen Plan: fusion reactors fueled by 2 hydrogen

isotopes: isotopes: deuterium and tritium deuterium and tritium (produce (produce helium, neutrons, and energy)helium, neutrons, and energy)

Problem: Achieving high temperatures required Problem: Achieving high temperatures required to start the reaction; containing the plasmato start the reaction; containing the plasma

Documents

Chapter 10 Nuclear Chemistry Section 10.1 Radioactivity Section 10.4 Fission and Fusion