1. Nuclear Chemistry Chapter 23 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PowerPoint Lecture Presentation by J. David Robertson University of Missouri

2. X A Z Mass Number Atomic Number Element Symbol Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons 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 1 1 1 0 0 0 +1 4 2 23.1

3. 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 235 92 + Cs 138 55 Rb 96 37 1n1n 0 ++ 2 235 + 1 = 138 + 96 + 2x1 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 235 92 + Cs 138 55 Rb 96 37 1n1n 0 ++ 2 92 + 0 = 55 + 37 + 2x0 23.1

4. 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 - 212 Po 4 He + A X 84 2Z 212 = 4 + AA = 208 84 = 2 + ZZ = 82 212 Po 4 He + 208 Pb 84 282 23.1

6. Nuclear Stability and Radioactive Decay Beta decay 14 C 14 N + 0  + 6 7 40 K 40 Ca + 0  + 19 20 1 n 1 p + 0  + 0 1 Decrease # of neutrons by 1 Increase # of protons by 1 Positron decay 11 C 11 B + 0  + 6 5 +1 38 K 38 Ar + 0  + 19 18 +1 1 p 1 n + 0  + 1 0 +1 Increase # of neutrons by 1 Decrease # of protons by 1 and have A = 0 and Z = 0 23.2

7. Electron capture decay Increase # of neutrons by 1 Decrease # of protons by 1 Nuclear Stability and Radioactive Decay 37 Ar + 0 e 37 Cl + 18 17 55 Fe + 0 e 55 Mn + 26 25 1 p + 0 e 1 n + 1 0 Alpha decay Decrease # of neutrons by 2 Decrease # of protons by 2 212 Po 4 He + 208 Pb 84 282 Spontaneous fission 252 Cf 2 125 In + 2 1 n 98 490 23.2

8. n/p too large beta decay X n/p too small positron decay or electron capture Y 23.2

9. Nuclear Stability Certain numbers of neutrons and protons are extra stable n or p = 2, 8, 20, 50, 82 and 126 Like extra stable numbers of electrons in noble gases (e - = 2, 10, 18, 36, 54 and 86) Nuclei with even numbers of both protons and neutrons are more stable than those with odd numbers of neutron and protons All isotopes of the elements with atomic numbers higher than 83 are radioactive All isotopes of Tc and Pm are radioactive 23.2

10. Nuclear binding energy (BE) is the energy required to break up a nucleus into its component protons and neutrons. BE + 19 F 9 1 p + 10 1 n 9 1 0 BE = 9 x (p mass) + 10 x (n mass) – 19 F mass E = mc 2 BE (amu) = 9 x 1.007825 + 10 x 1.008665 – 18.9984 BE = 0.1587 amu 1 amu = 1.49 x 10 -10 J BE = 2.37 x 10 -11 J binding energy per nucleon = binding energy number of nucleons = 2.37 x 10 -11 J 19 nucleons = 1.25 x 10 -12 J 23.2

11. Nuclear binding energy per nucleon vs Mass number nuclear binding energy nucleon nuclear stability 23.2

12. Kinetics of Radioactive Decay N daughter rate = - NN tt rate = N NN tt = N - N = N 0 exp(- t)lnN = lnN 0 - t N = the number of atoms at time t N 0 = the number of atoms at time t = 0 is the decay constant ln2 = t½t½ 23.3

13. Kinetics of Radioactive Decay [N] = [N] 0 exp(- t) ln[N] = ln[N] 0 - t [N] ln [N] 23.3

14. Radiocarbon Dating 14 N + 1 n 14 C + 1 H 716 0 14 C 14 N + 0  + 6 7 t ½ = 5730 years Uranium-238 Dating 238 U 206 Pb + 8 4  + 6 0  92822 t ½ = 4.51 x 10 9 years 23.3