chapter 22 nuclear chemistry. sect. 22-1: the nucleus nucleons – collective name for protons &...
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Sect. 22-1: The Nucleus Nucleons – collective name for protons &
neutrons Nuclide – an atom Notation: either radium – 228 or 228
88Ra
Mass Defect and Nuclear Stability Mass defect – difference between mass of
atom and sum of mass of p+, no, and e-
Cause???Mass was converted to energy when nucleus
was formed (E=mc2 where c=3.00 x 108m/s) Nuclear binding energy – energy released
when a nucleus forms
What is the mass defect of 3216S?
0.291764 amu What is the nuclear binding energy for that
same nuclide?4.36x10-11 J
Binding energy per nucleon – binding energy divided by # of nucleonsUsed to determine stability of nuclides
Higher # = more stable
Nuclides with even # of nucleons are typically more stableOnly 4 stable with odd # of p+ and no.
Nuclear shell model – nucleons exist in energy levels (shells) in the nucleus
Magic # - 2, 8, 20, 28, 50, 82, and 126… # of nucleons that represent completed energy levels (most stable)
Nuclear Reactions Nuclear reaction – reaction that affects
nucleus Transmutation – change in identity due to
change in # of protons
Sect. 22-2: Radioactive Decay Radioactive Decay – nucleus emitting
radiation, particles, or both Nuclear radiation – particles/radiation
that are released Radioactive nuclide – unstable
nuclide that decays
Types of Radioactive Decay Alpha particle – 2 p+ and 2 no bound
togetherSame as Helium nucleus2+ charge
Beta Particle – electron emitted from nucleusNeutron breaks into proton and electron…
electron is released1- charge
Positron – same mass as electron, but + chargeproton converts to neutron & positron is
released38
19K 3818Ar + 0
+1β
Electron capture – inner orbital electron is captured by the nucleusCombines with a proton to form neutron106
47Ag + 0-1e 106
46Pd
Gamma rays (γ) – high energy, no mass waves emitted from nucleusUsually accompanies one of the other types
of emission
Half- life(t½) – time it takes for ½ of the radioisotope to decayDifferent for every radioisotope# of t½ = time elapsed
length of one ½-life
Phosphorus-32 has a ½-life of 14.3 days. How many milligrams remain after 57.2 days if you start with 4.0mg of the isotope?
0.25mg
Decay series – multiple decays happen until a stable nuclide is reachedParent nuclide – heaviest in the
decay seriesDaughter nuclides – products of the
decay series
Artificial transmutation – bombardment of stable nuclei with charged & uncharged particlesParticle acceleratorTransuranium elements – elements past
uranium in periodic table Created by artificial transmutation All are radioactive
Radiation penetrating powerSkin/paper usually stops alphabeta only penetrates 1-2 cm into
body; need lead or glass to stop itGamma goes all the way through
body; need thick layers of lead or concrete
Sect. 22-3: Nuclear Radiation
Units of radiationRoentgenRem (roentgen equivalent, man)
Used for discussing human exposure to radiation
Sect. 22-3: Nuclear Radiation
Applications of Nuclear Radiation Radioactive dating Radioactive tracers in medicine Radioactive nuclides in agriculture
Nuclear Waste From fission reactions in power plants,
nuclear subs, and nuclear bombs Has very long half-lives Disposal is typically underground
Sect. 22-4: Nuclear Fission & Fusion Fission – nucleus splits apart Fusion – nuclei combine together Both release large amounts of energy,
fusion more than fission
Chain reaction – one product starts another reaction
Critical mass – minimum amount of nuclides needed to sustain a chain reaction