12 th edition

 Review from Ch. 2
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Subatomic particles
Atoms are neutral: # protons = # electrons
Isotopes
– atoms with same number of protons but different number of neutrons
Mass #
Atomic #


A
Z

Particle nucleon
Position Charge Mass (kg) electron outside nucleus −1 9.11 x 10 -31 proton inside nucleus neutron inside nucleus
+1
0
1.67 x 10 -27
1.67 x 10 -27

Nuclear Chemistry deals with only the nucleus.
 radioactivity – spontaneous emission of radiation
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 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 4
2
He or 4
2
α Common for heavy radionuclide beta ( β) particle gamma ( positron g
) ray
0
-1
β or 0
-1 e High-speed electrons; atomic number increases when a decay product
0
0 g
High-energy photons; often accompanies other decay like electron capture
0
1
β or 0
1 e Atomic number decreases when a decay product
Decay reactants: electron capture 0
-1 e neutron capture 1
0 n
Addition of electron(s) with production of g rays
Neutron capture causes transmutations and fission-based chain reactions

235

Nuclear Equations – sums of both mass and atomic numbers on both sides of equation are equal
Examples:
68
31
Ga + 0
-1 e → _____
212
87
Fr → 208
85
At + ______
263
106
Sg → ______ + 4
2
He

21.4 Rates of Radioactive Decay
 Radioactive decay follows 1 st order kinetics.
 All half-lives are equal.
ln


N
N
0 t


  kt
N – # of radioactive nuclei k – decay constant t
1 / 2

0 .
693 k
Individual half-lives vary tremendously:
214 Po 2 x 10 -4 s
144 Nd 5 x 10 15 year

Practice exercise, p. 890

Practice problem 21.33

Practice problem, 90 Sr from 1 st atomic explosion

Mastering problem 21.41