CHAPTER 25 Nuclear Chemistry
Post on 24-Jan-2016
DESCRIPTIONCHAPTER 25 Nuclear Chemistry. I. The Nucleus -Terms (p. 798-820). I. II. III. IV. Ionizing Radiation. Radiation is a form of energy transferred by waves or atomic particles - PowerPoint PPT Presentation
Nuclear ChemistryI. The Nucleus -Terms(p. 798-820)IIVIIIII
Ionizing RadiationRadiation is a form of energy transferred by waves or atomic particlesIonizing Radiation is any radiation with high enough energy to create ions (by knocking electrons out of atoms)like UV, X, gamma, and cosmic raysThere are both natural sources of radiation (unstable nuclei and stars) and human created sources
Zone of StabilityStable nuclei exist within the zone of stability seen on the graphnot always a 1:1 ratio of p+ to noOutside this range, nuclei are unstable and will decay (disintegrate) into new nuclei
DefinitionsNucleons = particles in nucleus (p+ and n0)Nuclide refers to the nucleus of an atomNuclear Reactions involve transmutation where one element become another. Radioactive Decay is the when unstable nuclei spontaneous lose energy by emitting ionizing particles; as this changes the nucleus of the atom, this also changes the type of element
Alpha Decay ProcessAlpha Particle(Helium Nucleus)(4.00147 amu)Parent NuclideAm-241U-238Th-232Ra-226Daughter NuclideNp-237Th-234Ra-228Rn-222
A. Mass DefectThe mass defect describes the mass lost during the formation of nucleiDifference between the mass of an atom and the mass of its individual particles.4.00260 amuMass of atom4.03298 amuMass of particles
B. Nuclear Binding EnergyEnergy released when a nucleus is formed from nucleons. This contributes to the loss in mass of nucleus, described by E = mc2.High binding energy = stable nucleus.E = mc2E:energy (J)m:mass defect (kg)c:speed of light (3.00108 m/s)
B. Nuclear Binding EnergyUnstable nuclides are radioactive and undergo radioactive decay.Iron (Fe) is the most stable nucleus!!
Nuclear ChemistryII. Radioactive Decay(p. 798-820)IIVIIIII
Types of Spontaneous RadiationAlpha particle ()helium nucleuspaper2+Beta particle or -electron1-woodPositron +positron1+Gamma ()high-energy photon0Lead orconcreteGreek symbolchargestopped by
Other Radiation particlesproton p+
+1neutron n00Greek symbolcharge
How does an electron get emitted from the nucleus?Basically a neutron splits into a proton which stays in the nucleus and an electron is emitted ( decay)n & p in nucleusn is really like a p and e togethern converted to a proton and an e is emitted++
Transmutation ReactionsI Alpha EmissionNumbers must balance on both sides of arrow!!238amu on left = (234 + 4amu)92 is nucl chrg on left = 90 + 2 on right
B. Nuclear DecayII Beta EmissionIII Positron Emission*a proton 1p is not the same as a positron 0e
B. Nuclear DecayIV Electron Capture
B. Nuclear DecayV Alpha Capture followed by neutron emissionGamma Emission causes no change in mass or charge and Usually follows the previous types of decay.
Beta (Negatron) Decay ProcessParent NucleusRhenium-187Potassium-40Daughter NucleusOsmium-187Calcium-40Beta Particle(electron)Antineutrino
Beta ParticlesSame as an electron with kinetic energyPositive or negative charge of 1May be positively or negatively chargedCan normally be stopped by 1 cm of plastic, wood, paperException for positron emitters
B. Nuclear DecayWhy nuclides decaypg. 803need stable ratio of neutrons to protonsDECAY SERIES TRANSPARENCY
C. Half-lifeHalf-life (t)Time required for half the atoms of a radioactive nuclide to decay.Shorter half-life = less stable.
C. Half-lifemf:final massmi:initial massn:# of half-lives
C. Half-lifeFluorine-21 has a half-life of 5.0 seconds. If you start with 25 g of fluorine-21, how many grams would remain after 60.0 s?GIVEN:t = 5.0 smi = 25 gmf = ?total time = 60.0 sn = 60.0s 5.0s =12 WORK:mf = mi ()nmf = (25 g)(0.5)12mf = 0.0061 g
Decay SeriesMany heavy elements are unstable and so they will continue to decay (be radioactive) until they finally transmute into a stable nucleus.Here is an example of the Th-232 decay seriesThorium oxide is used to in camping lanterns to intensify the brightness when on fire. Stable isotope
Alpha decay is a radioactive process in which a particle with two neutrons and two protons is ejected from the nucleus of a radioactive atom. The particle is identical to the nucleus of a helium atom.Alpha decay only occurs in very heavy elements such as uranium, thorium and radium. The nuclei of these atoms are very neutron rich (i.e. have a lot more neutrons in their nucleus than they do protons) which makes emission of the alpha particle possible. After an atom ejects an alpha particle, a new parent atom is formed which has two less neutrons and two less protons. Thus, when uranium-238 (which has a Z of 92) decays by alpha emission, thorium-234 is created (which has a Z of 90). Because alpha particles contain two protons, they have a positive charge of two. Further, alpha particles are very heavy and very energetic compared to other common types of radiation. These characteristics allow alpha particles to interact readily with materials they encounter, including air, causing many ionizations in a very short distance. Typical alpha particles will travel no more than a few centimeters in air and are stopped by a sheet of paper.
Show decay on chart of nuclides,Show smoke detector as application of alpha decay.Beta decay is a radioactive process in which an electron is emitted from the nucleus of a radioactive atom, along with an unusual particle called an antineutrino. The neutrino is an almost massless particle that carries away some of the energy from the decay process. Because this electron is from the nucleus of the atom, it is called a beta particle to distinguish it from the electrons which orbit the atom.Like alpha decay, beta decay occurs in isotopes which are neutron rich (i.e. have alot more neutrons in their nucleus than they do protons). Atoms which undergo beta decay are located below the line of stable elements on the chart of the nuclides, and are typically produced in nuclear reactors. When a nucleus ejects a beta particle, one of the neutrons in the nucleus is transformed into a proton. Since the number of protons in the nucleus has changed, a new daughter atom is formed which has one less neutron but one more proton than the parent. For example, when rhenium-187 decays (which has a Z of 75) by beta decay, osmium-187 is created (which has a Z of 76). Beta particles have a single negative charge and weigh only a small fraction of a neutron or proton. As a result, beta particles interact less readily with material than alpha particles. Depending on the beta particles energy (which depends on the radioactive atom), beta particles will travel up to several meters in air, and are stopped by thin layers of metal or plastic.Show compact fluorescent light bulb as application of beta decay.