Unit 8 - Chpt 19 - Nuclear Chemistry Radioactive Decay Nuclear Transformations Stability of nucleus Uses of radiation Fission and Fusion Effects of radiation HW set1: Chpt 19 - pg. 901-905 # 12, 14, 16, 20, 22, 26, 29, 34, 40, 42 - Due Tues. Apr 13
Radioactivity review Atomic Number (Z) – number of protons Mass Number (A) – sum of protons and neutrons Radioactive Decay - Nucleus undergoes decomposition to form a different nucleus.
Nuclear Stability - review Nuclides with 84 or more protons are unstable. Light nuclides are stable when Z equals A – Z (neutron/proton ratio is 1). For heavier elements the neutron/proton ratio required for stability is greater than 1 and increases with Z. Certain combinations of protons and neutrons seem to confer special stability. Even numbers of protons and neutrons are more often stable than those with odd numbers.
Nuclear Stability - review Certain specific numbers of protons or neutrons produce especially stable nuclides. 2, 8, 20, 28, 50, 82, and 126
Decay Processes Decay Series (Series of Alpha and Beta Decays)
Concept check Which decay process are the following? electron capture positron alpha particle beta particle If the atomic number is not provided, you need to look it up in the periodic table i.e. 129 Sb find Sb put in 51
Rate of decay Rate = kN The rate of decay is proportional to the number of nuclides. This represents a first-order process. Half-life - Time required for the number of nuclides to reach half the original value.
Rate problem We dont have to have an exact number of half-lives anymore, now that we know the rate is 1st order. A first order reaction is 35% complete at the end of 55 minutes. What is the value of k? HINT: go back to kinetics for 1st order
Nuclear Transformation The change of one element into another. Math is same as radioactive decay can solve for what may be missing
How to make collisions - new elements Schematic diagram of a cyclotron
Carbon-14 dating Used to date wood and cloth artifacts. Based on carbon – 14 to carbon – 12 ratio. Half-life 5730years
Radiotracer Applications Radioactive nuclides that are introduced into organisms in food or drugs and whose pathways can be traced by monitoring their radioactivity.
Energy Stability of Nucleus When a system gains or loses energy it also gains or loses a quantity of mass. E = mc 2 m = mass defect E = change in energy If E is negative (exothermic), mass is lost from the system.
Mass Defect Calculating the mass defect for : Since atomic masses include the masses of the electrons, we must account for the electron mass. nucleus is synthesized from 2 protons and two neutrons. Missing mass in binding energy
Binding Energy The energy required to decompose the nucleus into its components. Iron-56 is the most stable nucleus and has a binding energy of 8.97 MeV per nucleon. 931.5 MeV per amu
Fission or Fusion Fusion – Combining two light nuclei to form a heavier, more stable nucleus. Fission – Splitting a heavy nucleus into two nuclei with smaller mass numbers. (A self-sustaining fission process is called a chain reaction.) Fission or Fusion?