Chapter 23 N UCLEAR C HEMISTRY Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

C HEMICAL VS N UCLEAR R EACTIONS

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 N UCLEAR S YMBOLS

D ECAY P ARTICLES  Alpha(α) Particle  2 protons and 2 neutrons Helium nucleus  Gamma() Particle  Energy that accompanies a decay reaction 4 He 2 44 2 or 0γ0γ 0

D ECAY P ARTICLES  Beta( β ) Particles  electron  Positron 0e0e 00 or 0e0e +1 00 or

O THER P ARTICLES  Proton  Neutron 1p1p 1 1H1H 1 or 1n1n 0

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 B ALANCING N UCLEAR E QUATIONS

212 Po decays by alpha emission. 212 Po Po 4 He Pb P RACTICE P ROBLEM In radioactive decay steps, the beginning radioactive isotope is called the parent and the product is called the daughter.

U RANIUM D ECAY S ERIES

Beta decay 14 C 14 N + 0  Positron decay 11 C 11 B + 0  D ECAY E XAMPLES Electron capture decay 37 Ar + 0 e 37 Cl Alpha decay 212 Po 4 He Pb

Cyclotron Particle Accelerator 14 N + 4  17 O + 1 p Al + 4  30 P + 1 n N + 1 p 11 C + 4  N UCLEAR T RANSMUTATION Bombarding an element with particles to produce new elements

n/p too large beta decay X n/p too small positron decay or electron capture Y Band of 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 N UCLEAR S TABILITY

N UCLEAR B INDING E NERGY Nuclear binding energy (BE): energy required to break up a nucleus into its component protons and neutrons. Einstein’s energy mass relationship: E = mc 2 Links energy and mass calculations

BE + 19 F 9 1 p n BE = 9 x (p mass) + 10 x (n mass) – 19 F mass BE (amu) = 9 x x – BE = amux 1.49 x J 1 amu = 2.37 x J binding energy per nucleon = binding energy number of nucleons = 2.37 x J 19 nucleons = 1.25 x J H OW TO C ALCULATE BE

nuclear binding energy nucleon nuclear stability N UCLEAR BINDING ENERGY PER NUCLEON VS M ASS NUMBER

N UCLEAR F USION  Combining of small nuclei to form larger ones  Occurs in stars at high temperatures  Called a thermonuclear reaction

N UCLEAR F ISISON  Breaking down of a large massive atom into smaller ones  Nuclear chain reaction: self-sustaining sequence of nuclear fission reactions.  critical mass: minimum mass of fissionable material required to generate a self-sustaining nuclear chain reaction

Non-criticalCritical T WO T YPES OF F ISSION

Schematic diagram of a nuclear fission reactor C ONTROLLED N UCLEAR F ISSION

G EIGER -M ÜLLER C OUNTER