Download - Chapter 21 Lecture- Nuclear Chemistry
![Page 1: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/1.jpg)
Chapter 21Nuclear Chemistry
![Page 2: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/2.jpg)
Nuclear Chemistry
The nucleus of an atomcontains
protons (+1charge)and
neutrons (no charge)
![Page 3: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/3.jpg)
The nucleus is held togetherby the strong nuclear force
The strong nuclear force is the strongestforce known
Protons and neutrons are very closetogether
They exchange a teeny bit of mass backand forth.
When disrupted, the mass is convertedto energy according to E=mc2
The mass is tiny. The energy isimmense.
![Page 4: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/4.jpg)
Protons and neutrons experiencethe strong nuclear force if close
enough
Because protons repel each otherthe nucleus needs a certain proton
to neutron ratio for stability
![Page 5: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/5.jpg)
An unstable atom decays byemitting radiation
These unstable atoms are radioactive.Carbon-12 is stable. Carbon-14 is
radioactive.Carbon-14 is a radioisotope.There are many naturally occurring
radioisotopes and some that are human-made.
![Page 6: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/6.jpg)
Radioisotopes decay intostable isotopes of a
DIFFERENT element
In nuclear reactions, the makeup of thenucleus changes.
Sometimes the number of protons willchange.
If the number of protons changes, theelement has changed.
![Page 7: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/7.jpg)
The three most commonforms of radioactive decay are
alpha(α), beta(β) andgamma(γ)
![Page 8: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/8.jpg)
Alpha particles are the leastpenetrating.
Gamma rays are the mostpenetrating.
25.1
![Page 9: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/9.jpg)
To balance nuclear equationsyou must know the symbol for
the emitted particle
You must balance the atomic number (number onbottom) and the atomic mass (number on top)
Here 222 + 4 = 226 and 86 + 2 = 88 its balanced
![Page 10: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/10.jpg)
The stuff that radiatesAn alpha particle is a helium nucleus it
has a +2 charge and a mass of 4amu.
![Page 11: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/11.jpg)
A beta particle is an electronwhich is formed when a
neutron becomes a proton
![Page 12: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/12.jpg)
A gamma ray is a high energyelectromagnetic wave.
A gamma ray has no mass orcharge so it is not in a nuclear
equation.
![Page 13: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/13.jpg)
particle Alpha α Beta β Gamma γMass 4amu 0 0Charge +2 -1 0Effect Radioisotope
loses twoprotons and twoneutronsThe ELEMENTchanges
Radioisotopeconverts a neutronto a proton &ejects an electronThe ELEMENTchanges
Radioisotopeloses energyThe elementdoes notchange
What it is Heliumnucleus
electron High energyelectromagneticradiation
Stop it Paper/skin 1cm/metal foil Lead/concretedamage High ionization Medium
ionizationLowestionization
![Page 14: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/14.jpg)
Damage from nuclearradiation is due to ionization of
living tissue.Nuclear radiation is called ionizing
radiation because it produces ions fromneutral molecules.
Alpha radiation has a low penetration, butit is the most damaging to living tissuebecause it deposits all its energy alonga short path
![Page 15: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/15.jpg)
Nuclear Fission
Fission separates heavy elements into two lighterelements.
Uranium-235 Barium-141 + Krypton-92
+3neutrons
A huge amount of energy is produced.Used by humans as an energy sourceThe fission bomb was used in WWII
![Page 16: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/16.jpg)
Nuclear fusion
Fusion combines two light nuclei into oneheavier element.
Produces even more energy than fission.Occurs in the sun.Requires extremely high temperatures
and pressures.
![Page 17: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/17.jpg)
FUSION = to put togetherFISSION = to break apart
![Page 18: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/18.jpg)
The Nucleus
• Remember that the nucleus is comprised ofthe two nucleons, protons and neutrons.
• The number of protons is the atomic number.• The number of protons and neutrons together
is effectively the mass of the atom.
![Page 19: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/19.jpg)
Isotopes
• Not all atoms of the same element havethe same mass due to differentnumbers of neutrons in those atoms.
• There are three naturally occurringisotopes of uranium:Uranium-234Uranium-235Uranium-238
![Page 20: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/20.jpg)
Radioactivity
• It is not uncommon for some nuclides ofan element to be unstable, orradioactive.
• We refer to these as radionuclides.• There are several ways radionuclides
can decay into a different nuclide.
![Page 21: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/21.jpg)
Types ofRadioactive Decay
![Page 22: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/22.jpg)
Alpha Decay:
Loss of an α-particle (a helium nucleus)
He42
U23892
→ U23490 He4
2+
![Page 23: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/23.jpg)
Beta Decay:
Loss of a β-particle (a high energy electron)
β0−1 e0
−1or
I13153 Xe131
54→ + e0
−1
![Page 24: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/24.jpg)
Positron Emission:
Loss of a positron (a particle that has thesame mass as but opposite charge thanan electron)
e01
C116
→ B115 + e0
1
![Page 25: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/25.jpg)
Gamma Emission:
Loss of a γ-ray (high-energy radiationthat almost always accompanies the lossof a nuclear particle)
γ00
![Page 26: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/26.jpg)
Electron Capture (K-Capture)
Addition of an electron to a proton in thenucleusAs a result, a proton is transformed into a
neutron.p1
1 + e0−1
→ n10
![Page 27: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/27.jpg)
Neutron-Proton Ratios
• Any element with morethan one proton (i.e.,anything but hydrogen)will have repulsionsbetween the protons inthe nucleus.
• A strong nuclear forcehelps keep the nucleusfrom flying apart.
![Page 28: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/28.jpg)
Neutron-Proton Ratios
• Neutrons play a key rolestabilizing the nucleus.
• Therefore, the ratio ofneutrons to protons is animportant factor.
![Page 29: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/29.jpg)
Neutron-Proton Ratios
For smaller nuclei(Z ≤ 20) stablenuclei have aneutron-to-protonratio close to 1:1.
![Page 30: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/30.jpg)
Neutron-Proton Ratios
As nuclei getlarger, it takes agreater number ofneutrons tostabilize thenucleus.
![Page 31: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/31.jpg)
Stable Nuclei
The shaded region inthe figure showswhat nuclides wouldbe stable, the so-called belt of stability.
![Page 32: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/32.jpg)
Stable Nuclei
• Nuclei above thisbelt have too manyneutrons.
• They tend to decayby emitting betaparticles.
![Page 33: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/33.jpg)
Stable Nuclei
• Nuclei below the belthave too manyprotons.
• They tend tobecome more stableby positron emissionor electron capture.
![Page 34: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/34.jpg)
Stable Nuclei
• There are no stable nuclei with anatomic number greater than 83.
• These nuclei tend to decay by alphaemission.
![Page 35: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/35.jpg)
![Page 36: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/36.jpg)
Radioactive Series
• Large radioactivenuclei cannot stabilizeby undergoing onlyone nucleartransformation.
• They undergo a seriesof decays until theyform a stable nuclide(often a nuclide oflead).
![Page 37: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/37.jpg)
Some Trends
Nuclei with 2, 8, 20,28, 50, or 82 protonsor 2, 8, 20, 28, 50,82, or 126 neutronstend to be morestable than nuclideswith a differentnumber of nucleons.
![Page 38: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/38.jpg)
Some Trends
Nuclei with an evennumber of protonsand neutrons tend tobe more stable thannuclides that haveodd numbers ofthese nucleons.
![Page 39: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/39.jpg)
Nuclear Transformations
Nucleartransformationscan be inducedby acceleratinga particle andcolliding it withthe nuclide.
![Page 40: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/40.jpg)
Particle AcceleratorsThese particle accelerators are enormous,having circular tracks with radii that aremiles long.
![Page 41: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/41.jpg)
Kinetics of Radioactive Decay
• Nuclear transmutation is a first-orderprocess.
• The kinetics of such a process, you willrecall, obey this equation:
= kt NtN0
ln
ln[A]t – ln[A]0 = -kt for 1st order kinetics
![Page 42: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/42.jpg)
Kinetics of Radioactive Decay
• The half-life of such a process is:
= t1/2 0.693
k
• Comparing the amount of a radioactivenuclide present at a given point in timewith the amount normally present, onecan find the age of an object.
Not given, but canbe derived fromprevious equationwith [A]t equal tohalf of [A]0.
![Page 43: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/43.jpg)
First order processes (including nuclear decay)always show a constant half-life
![Page 44: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/44.jpg)
Measuring Radioactivity
• One can use a device like this Geiger counter tomeasure the amount of activity present in aradioactive sample.
• The ionizing radiation creates ions, which conducta current that is detected by the instrument.
![Page 45: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/45.jpg)
Kinetics of Radioactive Decay
A wooden object from an archeological siteis subjected to radiocarbon dating. Theactivity of the sample that is due to 14C ismeasured to be 11.6 disintegrations persecond. The activity of a carbon sample ofequal mass from fresh wood is 15.2disintegrations per second. The half-life of14C is 5715 yr. What is the age of thearcheological sample?
![Page 46: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/46.jpg)
Kinetics of Radioactive Decay
First we need to determine the rateconstant, k, for the process.
= t1/2 0.693
k
= 5715 yr 0.693k
= k 0.6935715 yr
= k 1.21 × 10−4 yr−1
![Page 47: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/47.jpg)
Kinetics of Radioactive Decay
Now we can determine t:
= kt NtN0
ln
= (1.21 × 10−4 yr−1) t 11.615.2ln
= (1.21 × 10−4 yr−1) t ln 0.763= t 6310 yr
![Page 48: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/48.jpg)
Energy in Nuclear Reactions
• There is a tremendous amount ofenergy stored in nuclei.
• Einstein’s famous equation, E = mc2,relates directly to the calculation of thisenergy.
![Page 49: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/49.jpg)
Energy in Nuclear Reactions
• In the types of chemical reactions wehave encountered previously, theamount of mass converted to energyhas been minimal.
• However, these energies are manythousands of times greater in nuclearreactions.
![Page 50: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/50.jpg)
Energy in Nuclear Reactions
For example, the mass change for the decayof 1 mol of uranium-238 is −0.0046 g.The change in energy, ΔE, is then
ΔE = (Δm) c2
ΔE = (−4.6 × 10−6 kg)(3.00 × 108 m/s)2
ΔE = −4.1 × 1011 J
![Page 51: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/51.jpg)
Nuclear Fission
• How does one tap all that energy?• Nuclear fission is the type of reaction carried
out in nuclear reactors.
![Page 52: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/52.jpg)
Nuclear Fission
• Bombardment of the radioactive nuclide witha neutron starts the process.
• Neutrons released in the transmutation strikeother nuclei, causing their decay and theproduction of more neutrons.
![Page 53: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/53.jpg)
Nuclear Fission
This process continues in what we call anuclear chain reaction.
![Page 54: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/54.jpg)
Nuclear Fission
If there are not enough radioactive nuclides in thepath of the ejected neutrons, the chain reactionwill die out.
![Page 55: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/55.jpg)
Nuclear Fission
Therefore, there must be a certain minimumamount of fissionable material present for thechain reaction to be sustained: Critical Mass.
![Page 56: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/56.jpg)
Fission reactor
![Page 57: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/57.jpg)
Nuclear ReactorsIn nuclear reactors the heat generated by thereaction is used to produce steam that turns aturbine connected to a generator.
![Page 58: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/58.jpg)
Nuclear Reactors• The reaction is kept in
check by the use ofcontrol rods.
• These block the paths ofsome neutrons, keepingthe system from reachinga dangerous supercriticalmass.
![Page 59: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/59.jpg)
Nuclear Fusion
• Fusion would be a superiormethod of generatingpower.The good news is that the
products of the reaction arenot radioactive.
The bad news is that inorder to achieve fusion, thematerial must be in theplasma state at severalmillion kelvins.
![Page 60: Chapter 21 Lecture- Nuclear Chemistry](https://reader034.vdocuments.us/reader034/viewer/2022052410/554a5a2fb4c905522f8b4f82/html5/thumbnails/60.jpg)
Nuclear Fusion
• Tokamak apparati like theone shown at the rightshow promise for carryingout these reactions.
• They use magnetic fieldsto heat the material.