Chapter 22 Nuclear Chemistry

Sect. 22-1: The Nucleus Nucleons – collective name for protons & neutrons Nuclide – an atom Notation: either radium – 228 or Ra

Mass Defect and Nuclear Stability Mass defect – difference between mass of atom and sum of mass of p +, n o, and e - Cause???  Mass was converted to energy when nucleus was formed (E=mc 2 where c=3.00 x 10 8 m/s) Nuclear binding energy – energy released when a nucleus forms

What is the mass defect of S?  amu What is the nuclear binding energy for that same nuclide?  4.36x J

Binding energy per nucleon – binding energy divided by # of nucleons  Used 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 stable  Only 4 stable with odd # of p + and n o. 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 n o bound together  Same as Helium nucleus  2+ charge

Beta Particle – electron emitted from nucleus  Neutron breaks into proton and electron…electron is released  1- charge

Positron – same mass as electron, but + charge  proton converts to neutron & positron is released  K  Ar β

Electron capture – inner orbital electron is captured by the nucleus  Combines with a proton to form neutron  Ag e  Pd

Gamma rays (γ) – high energy, no mass waves emitted from nucleus  Usually accompanies one of the other types of emission

Half- life(t ½ ) – time it takes for ½ of the radioisotope to decay  Different for every radioisotope  # of t ½ = 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 reached  Parent nuclide – heaviest in the decay series  Daughter nuclides – products of the decay series

Artificial transmutation – bombardment of stable nuclei with charged & uncharged particles  Particle accelerator  Transuranium elements – elements past uranium in periodic table Created by artificial transmutation All are radioactive

Radiation penetrating power  Skin/paper usually stops alpha  beta only penetrates 1-2 cm into body; need lead or glass to stop it  Gamma goes all the way through body; need thick layers of lead or concrete Sect. 22-3: Nuclear Radiation

Units of radiation  Roentgen  Rem (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