chapter 21 nuclear chemistry 12 th edition. 21.1 radioactivity review from ch. 2 subatomic particles...
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Chapter 21Nuclear 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
nucleonproton inside nucleus +1 1.67 x 10-27
neutron inside nucleus 0 1.67 x 10-27
symbolelementXAMassZAtomic
##
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 4
2α 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 0
1e 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
Nuclear Equations – sums of both mass and atomic numbers on both sides of equation are equal
Examples:68
31Ga + 0-1e → _____
21287Fr → 208
85At + ______
263106Sg → ______ + 4
2He
21.4 Rates of Radioactive Decay Radioactive decay follows 1st order kinetics. All half-lives are equal.
ktN
N t
0
ln N – # of radioactive nucleik – decay constant
Individual half-lives vary tremendously:
214Po 2 x 10-4 s144Nd 5 x 1015 yeark
t693.0
2/1
Half-lives
Practice exercise, p. 890
Practice problem 21.33
Practice problem, 90Sr from 1st atomic explosion
Mastering problem 21.41