Chapter 21Nuclear Chemistry

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. nuclide – nucleus with specified number of protons

and neutrons radioactivity – spontaneous emission of radiation 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:

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 capturepositron 0

1β or 01e Atomic number decreases when a decay

productDecay reactants:

electron capture 0-1e Addition of electron(s) with production of

g raysfission 1

0n Neutron capture causes chain reactions

Fission of 235U initiated by neutron capture

Chain Fission Reaction

Nuclear Equations – sum 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.

ktNN t

0

ln N – # of radioactive nucleik – decay constant

Individual half-lives vary tremendously

214Po 2 x 10-4 s144Nd 5 x 1015 yeark

t 693.02/1

Half-lives

Practice exercise, p. 907

Practice problem 21.33

Practice problem, 90Sr from 1st atomic explosion