Chapter 21 Nuclear Chemistry 12th edition

21.1 Radioactivity Review from Ch. 2 Subatomic particles Atoms are neutral: # protons = # electrons Isotopes – atoms with same number of protons but different number of neutrons Particle Position Charge Mass (kg) electron outside nucleus −1 9.11 x 10-31 nucleon proton inside nucleus +1 1.67 x 10-27 neutron

Nuclear Chemistry deals with only the nucleus. radioactivity – spontaneous emission of radiation nuclide – nucleus with specified number of protons and neutrons radionuclide – radioactive nuclide radioisotopes – atoms containing radioactive nuclei radioactive decay – spontaneous decomposition to form a different, more stable, nucleus with the production of one or more particles decay series – multiple decay steps through which radioactive nuclides go to reach a stable state

Decay Series

Common Particles in Radioactive Decay and Nuclear Reactions Decay products: (See Tables 21.2 and 21.3, p. 879) alpha (α) particle 42He or 42α Common for heavy radionuclide beta (β) particle 0-1β or 0-1e High-speed electrons; atomic number increases when a decay product gamma (g) ray 00g High-energy photons; often accompanies other decay like electron capture positron 01β or 01e Atomic number decreases when a decay product Decay reactants: electron capture 0-1e Addition of electron(s) with production of g rays neutron capture 10n Neutron capture causes transmutations and fission-based chain reactions

Fission of 235U initiated by neutron capture

Chain Fission Reaction

Examples: 6831Ga + 0-1e → _____ 21287Fr → 20885At + ______ Nuclear Equations – sums of both mass and atomic numbers on both sides of equation are equal Examples: 6831Ga + 0-1e → _____ 21287Fr → 20885At + ______ 263106Sg → ______ + 42He

21.4 Rates of Radioactive Decay Radioactive decay follows 1st order kinetics. All half-lives are equal. N – # of radioactive nuclei k – decay constant Individual half-lives vary tremendously: 214Po 2 x 10-4 s 144Nd 5 x 1015 year

Half-lives

Practice exercise, p. 890

Practice problem 21.33

Practice problem, 90Sr from 1st atomic explosion

Mastering problem 21.41