CHAPTER 22 Nuclear Chemistry I. The Nucleus (p. 701 - 704) II III IV

A. Mass Defect Difference between the mass of an atom and the mass of its individual particles. 4.00260 amu 4.03298 amu

B. Nuclear Binding Energy Energy released when a nucleus is formed from nucleons. High binding energy = stable nucleus. E = mc2 E: energy (J) m: mass defect (kg) c: speed of light (3.00×108 m/s)

B. Nuclear Binding Energy Unstable nuclides are radioactive and undergo radioactive decay.

Stable Nuclei

CHAPTER 22 Nuclear Chemistry II. Radioactive Decay (p. 705 - 712) II III IV

A. Types of Radiation 2+ 1- 1+ Alpha particle () helium nucleus paper 2+ Beta particle (-) electron 1- lead Positron (+) positron 1+ concrete Gamma () high-energy photon

B. Nuclear Decay Numbers must balance!! Alpha Emission parent nuclide daughter nuclide alpha particle Numbers must balance!!

B. Nuclear Decay Beta Emission electron Positron Emission positron

B. Nuclear Decay Electron Capture electron Gamma Emission Usually follows other types of decay. Transmutation One element becomes another.

B. Nuclear Decay Why nuclides decay… need stable ratio of neutrons to protons DECAY SERIES TRANSPARENCY

B. Synthetic Elements Transuranium Elements elements with atomic #s above 92 synthetically produced in nuclear reactors and accelerators most decay very rapidly

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C. Radioactive Dating half-life measurements of radioactive elements are used to determine the age of an object decay rate indicates amount of radioactive material EX: 14C - up to 40,000 years 238U and 40K - over 300,000 years

Radiation treatment using D. Nuclear Medicine Radioisotope Tracers absorbed by specific organs and used to diagnose diseases Radiation Treatment larger doses are used to kill cancerous cells in targeted organs internal or external radiation source Radiation treatment using -rays from cobalt-60.

F. Others Food Irradiation  radiation is used to kill bacteria Radioactive Tracers explore chemical pathways trace water flow study plant growth, photosynthesis Consumer Products ionizing smoke detectors - 241Am

Half Life The rate at which radioactive nuclides decay is dependent upon the amount of the nuclide present to begin with. Decay rate is usually expressed in terms of half life, the amount of time it takes for half of a sample to decay.

Illustrative Example - 20 min. Half Life Original sample 32 nuclei After 20 min., half is left. After another 20 min., one fourth is left. One eighth is left after another 20 min. Number of atoms decayed:

Another Example

C. Half-life Half-life (t½) Time required for half the atoms of a radioactive nuclide to decay. Shorter half-life = less stable.

The half-life of cobalt-60 is 10. 47 minutes The half-life of cobalt-60 is 10.47 minutes. How many mg of cobalt-60 remain after 104.7 minutes if you start with 10.0 mg?

C. Half-life mf: final mass mi: initial mass n: # of half-lives

C. Half-life t½ = 5.0 s mf = mi (½)n mi = 25 g mf = (25 g)(0.5)12 Fluorine-21 has a half-life of 5.0 seconds. If you start with 25 g of fluorine-21, how many grams would remain after 60.0 s? GIVEN: t½ = 5.0 s mi = 25 g mf = ? total time = 60.0 s n = 60.0s ÷ 5.0s =12 WORK: mf = mi (½)n mf = (25 g)(0.5)12 mf = 0.0061 g