Chapter 22

Nuclear Chemistry

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

Nucleus and Nuclear Stability Band of stability Small, 1:1 is

stable Large 1.5:1 is

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

Radiation Detection Film badges Geiger-Mϋller counters Scintillation counters

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

Nuclear power plants Shielding – radiation absorbing material Fuel - typically Uranium-235 Control Rods – neutron-absorbing; used to

slow down/stop reaction Moderator – slows down fast neutrons Coolant - water