Nuclear Chemistry

Radioactivity Antoine Henri Becquerel ( ) Discovered radioactivity accidentally while experimenting with photographic film.

Radioactivity Discovered polonium and radiumDiscovered polonium and radium Coined the term “radioactivity”Coined the term “radioactivity” Marie Curie ( )

Nuclear Reactions vs. Normal Chemical Changes Nuclear reactions involve changes in the nucleusNuclear reactions involve changes in the nucleus The splitting of the nucleus releases a tremendous amount of energy that holds the nucleus together – called binding energyThe splitting of the nucleus releases a tremendous amount of energy that holds the nucleus together – called binding energy “Normal” Chemical Reactions involve electrons, not the nucleus“Normal” Chemical Reactions involve electrons, not the nucleus

Types of Radiation Alpha (ά) – a positively charged helium isotope Alpha (ά) – a positively charged helium isotope Beta (β) – an electronBeta (β) – an electron Gamma (γ) – pure energy; called a ray rather than a particleGamma (γ) – pure energy; called a ray rather than a particle

Other Nuclear Particles Neutron Neutron Positron – a positive electron Positron – a positive electron

Penetrating Ability

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 A Z 1n1n 0 neutron 0e0e 00 or Beta particle 0e0e +1 positron 4 He 2 44 2 or alpha particle Symbol Format

Balancing Nuclear Reactions The reactants (starting materials – on the left side of an equation) and products (final products – on the right side of an equation) Atomic numbers must balance and Mass numbers must balance

Balancing Nuclear Equations 1.Conserve mass number (A). 1n1n 0 U Cs Rb n1n ( ) = 236 ( x1) = Conserve atomic number (Z) or nuclear charge. 1n1n 0 U Cs Rb n1n = x0 23.1

Nuclear Reactions Alpha emissionAlpha emission Note that mass number (A) goes down by 4 and atomic number (Z) goes down by  ? Rn Ra

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

Nuclear Reactions Beta emissionBeta emission Note that mass number (A) is unchanged and atomic number (Z) goes up by  ? UNp 238  UNp 

Other Types of Nuclear Reactions Positron ( 0 +1  ): a positive electron Electron capture: Electron capture: the capture of an electron 207

Learning Check What radioactive isotope is produced in the following bombardment of boron? 10 B + 4 He ? + 1 n 5 2 0

Learning Check What radioactive isotope is produced in the following bombardment of boron? 10 B + 4 He 13 N + 1 n

Write Nuclear Equations! Write the nuclear equation for the beta emitter Co Co 0 e+ 60 Ni

Artificial Nuclear Reactions New elements or new isotopes of known elements are produced by bombarding an atom with a subatomic particle such as a proton or neutron -- or even a much heavier particle such as 4 He and 11 B. Reactions using neutrons are called  reactions because a  ray is usually emitted

Artificial Nuclear Reactions Example of a  reaction is production of radioactive 31 P for use in studies of P uptake in the body P n ---> P + 

Transuranium Elements Elements beyond 92 (transuranium) made by starting with a  reaction U n ---> U +  U ---> Np  Np ---> Pu  Np ---> Pu 

Half-Life HALF-LIFE is the time that it takes for 1/2 a sample to decompose.HALF-LIFE is the time that it takes for 1/2 a sample to decompose. The rate of a nuclear transformation depends only on the “reactant” concentration.The rate of a nuclear transformation depends only on the “reactant” concentration.

Half-Life Decay of 20.0 mg of 15 O. What remains after 3 half-lives? After 5 half-lives?

Kinetics of Radioactive Decay For each duration (half-life), one half of the substance decomposes. For example: Ra-234 has a half-life of 3.6 days  If you start with 50 grams of Ra-234 After 3.6 days > 25 grams After 7.2 days > 12.5 grams After 10.8 days > 6.25 grams

Radiocarbon Dating Radioactive C-14 is formed in the upper atmosphere by nuclear reactions initiated by neutrons in cosmic radiation 14 N + 1 o n ---> 14 C + 1 H The C-14 is oxidized to CO 2, which circulates through the biosphere. When a plant dies, the C-14 is not replenished. But the C-14 continues to decay with t 1/2 = 5730 years. Activity of a sample can be used to date the sample.

Geiger Counter Used to detect radioactive substances

Learning Check! The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 39 hours? 39 hr./13 hr. = 3 half lives 64g x ½ = 32g x ½ = 16g x ½ = 8g will be left after 3 half lives. 0R 64/8 = 8 grams

Nuclear Fission

Representation of a fission process.

Nuclear Fission & POWER Currently about 103 nuclear power plants in the U.S. and about 435 worldwide.Currently about 103 nuclear power plants in the U.S. and about 435 worldwide. 17% of the world’s energy comes from nuclear.17% of the world’s energy comes from nuclear.

Figure 19.6: Diagram of a nuclear power plant.

Nuclear Fusion Fusion small nuclei combine 2 H + 3 H 4 He + 1 n Occurs in the sun and other stars Energy

Effects of Radiation

Band of Stability and Radioactive Decay

Nuclear Medicine: Imaging Thyroid imaging using Tc-99m

Food Irradiation Food can be irradiated with  rays from 60 Co or 137 Cs.Food can be irradiated with  rays from 60 Co or 137 Cs. Irradiated milk has a shelf life of 3 mo. without refrigeration.Irradiated milk has a shelf life of 3 mo. without refrigeration. USDA has approved irradiation of meats and eggs.USDA has approved irradiation of meats and eggs.