Nuclear Chemistry Chapter 23 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The symbols for various chemical elements and numbers of electrons, protons and neutrons in every species. Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons X A Z Mass Number Atomic Number Element Symbol A Z 1p1p 1 1H1H 1 or proton 1n1n 0 neutron 0e0e 00 or electron 0e0e +1 00 or positron 4 He 2 44 2 or  particle

Balancing Nuclear Equations 1.Conserve mass number (A). The sum of protons plus neutrons in the products must equal the sum of protons plus neutrons in the reactants. 1n1n 0 U Cs Rb n1n = x1 2.Conserve atomic number (Z) or nuclear charge. The sum of nuclear charges in the products must equal the sum of nuclear charges in the reactants. 1n1n 0 U Cs Rb n1n = x0 23.1

212 Po decays by alpha emission. Write the balanced nuclear equation for the decay of 212 Po. 4 He 2 44 2 or alpha particle Po 4 He + A X 84 2Z 212 = 4 + AA = = 2 + ZZ = Po 4 He Pb

Worked Example 23.1

Worked Example 23.3

Nuclear Stability and Radioactive Decay Beta decay 14 C 14 N + 0  K 40 Ca + 0  n 1 p + 0  Decrease # of neutrons by 1 Increase # of protons by 1 Positron decay 11 C 11 B + 0  K 38 Ar + 0  p 1 n + 0  Increase # of neutrons by 1 Decrease # of protons by 1 and have A = 0 and Z =

Electron capture decay Increase # of neutrons by 1 Decrease # of protons by 1 37 Ar + 0 e 37 Cl Fe + 0 e 55 Mn p + 0 e 1 n Alpha decay Decrease # of neutrons by 2 Decrease # of protons by Po 4 He Pb Spontaneous fission 252 Cf In n

The radioactive decay series Is a sequence of nuclear reaction that ultimately result in the formation of a stable isotope. The decay series of naturally occurring uranium-238 to thorium- 234 involves 14 steps. The decay scheme, also shows the half – lives of all the products. The beginning radioactive isotope in the series is called the parent and the product, the daughter. 238 U Parent 206 Pb daughter natural radioactivity

Kinetics of Radioactive Decay [N] = [N] 0 exp(- t)ln[N] = ln[N] 0 - t [N] ln [N] 23.3 rate = - NN tt rate = N NN tt = N - N = the number of atoms at time t N 0 = the number of atoms at time t = 0 is the decay constant ln2 = t½t½ [N] t [N] 0 = - t ln All radioactive decays obey first –order kinetics.

Problems

1 – 2 – 3 – 4 – 5 – 6 – 7 – 23 – 25 – 28 – 29 – 31 – 33 – 34 – 35 – 36 – 55 – 57 – 59