Radioactivity: Spontaneous emission of particles or electromagnetic radiation from unstable nuclei.
Stability: All elements with atomic number (Z) greater than 83 are radioactive.
Comparison of Reactions:
Chemical Reactions:
Atoms rearranged by breaking/forming bonds.
No elements changed into others.
Involves electrons.
Generally release small energy amounts.
Nuclear Reactions:
Converts elements into different elements or isotopes.
Involves protons, neutrons, and more subatomic particles.
Releases tremendous energy.
Reaction rates unaffected by temperature, pressure, catalysts.
20.2 Nuclear Stability
Neutron-to-Proton Ratio (n/p): Key factor for stability.
Stable nuclei typically have certain magic numbers (2, 8, 20, 50, 82, 126).
Isotopes with Z > 83 and certain others are radioactive.
Belt of Stability: Graphical representation showing stable nuclei; most radioactive nuclei fall outside this belt.
20.3 Kinetics of Radioactive Decay
Radioactive decays follow first-order kinetics.
Half-life: Time taken for half of a radioactive sample to decay; calculated using:
[ \ln[At] = -kt + \ln[A0] ]
Example: Carbon-14 dating uses decays to determine the age of artifacts through activity reduction over half-lives.
20.4 Nuclear Transmutation
Definition: Change of one element into another caused by nuclear reaction, often through particle collision.
Transuranium Elements: Elements with atomic numbers above 92 synthesized by particle accelerators.
20.5 Nuclear Fission
Fission: Splitting of a heavy nucleus into smaller nuclei with the release of neutrons and energy.
Chain Reaction: A self-sustaining series of nuclear fissions, requiring a minimum quantity called critical mass.
Applications: Nuclear reactors use controlled fission to generate energy.
20.6 Nuclear Fusion
Fusion: Combining of small nuclei to form larger ones, releasing energy.
Occurs in stars, including the sun, under high temperature and pressure conditions.
Future fusion energy solutions being explored include laser containment methods.
20.7 Use of Isotopes
Chemical Analysis: Isotopes are used for determining molecular structures. Example: Radioactive sulfur-35 used as a label in molecular studies.
Isotopes in Medicine: Tracers in diagnosis.
Sodium-24 for blood flow.
Iodine-131 for thyroid evaluation.
Iodine-123 for brain imaging.
20.8 Biological Effects of Radiation
Units of Measurement:
Curie (Ci): Disintegrations per second, measures radioactivity.
Rad: Radiation absorbed dose, indicates amount absorbed by tissues.
Rem: Effective dose calculated by multiplying rads by relative biological effective (RBE).
Average yearly radiation doses for Americans vary across different sources, from cosmic rays to nuclear waste.
Key Points Summary
Types of radioactive decay, kinetics of radioactive decay, nuclear stability, binding energy, fission and fusion processes, use of isotopes, biological effects, and application insights in various fields like medicine and chemical analysis are fundamental aspects of nuclear chemistry.