Text Book: Chapter 28 Review Book: Topic 12 Nuclear Chemistry Text Book: Chapter 28 Review Book: Topic 12

Nuclear Chemistry: Stability Transmutation: is a change in the atomic nucleus of one into that of another. Stability of nuclei is determined by the ratio of neutrons to protons. The ratio in all nuclei with an atomic number greater than 83 is UNSTABLE. Because they are unstable, elements with atomic number greater than 83 are also RADIOACTIVE! An unstable isotope is called a Radioisotope.

Nuclear Decay Unstable nuclei decay in a series of steps to eventually produce a stable nucleus in the “belt or stability”. During this decay, the nucleus emits radiation in the form of alpha, beta particles, positrons, and/or gamma radiation. Radiation can be dangerous to living tissue and cause mutations in DNA!!

Number of neutrons= twice the number of protons Equal number of protons and neutrons

Decay Particles Alpha particles: a helium nucleus composed of two protons and two neutrons represented by the symbols Beta particles: is an electron whose source is atomic nucleus (β-) Positron: is identical to an electrons except that it is positive (β+) Almost all nuclear decay releases some energy in the form of gamma rays: (γ) which are similar to X-rays but with greater energy.

Alpha Decay When a nucleus emits this particle it is called an alpha emitter. Nucleus that emits an alpha particle will decrease by two and its mass number decreases by 4 Example: Radium-226 will have an atomic number that changes from 88 to 86 and a mass change from 226 to 222, becoming radon. Overview: Atomic number decreases by two Number of protons decreases by two Number of neutrons decreases by two Mass number decreases by 4

Beta Decay Nuclei that emit beta particles as a result of nuclear disintergration are called beta emitters. Nucleus that emits a beta particle will increase in charge by one and increase in atomic mass by one. Overview: Atomic number increases by one Number if protons increases by one Number of neutrons decreases by one Mass number remains the same

Positron Emission When a nucleus emits a positron, the charge on the nucleus decreases by one and the atomic number decreases by one. Overview: Atomic number decreases by one Number of protons decreases by one Number of neutrons decreases by one Mass number remains the same

Nuclear Equations As in all chemical equations, nuclear equations must have a balanced mass and charge on both sides of the equation. Example: 147N +42He 178O + 11H The sum of the charges on both sides is 9 and the mass on both sides is 18 Using the concept on conservation of charge and mass, you can find the missing particle of an equation.

You Try! 2713Al +10n 2411Na + X X would have to satisfy the missing charge and mass. In this problem X would equal 42He, so X is an alpha particle!

Transmutation There are two types of Transmutations: Natural and Artificial. Natural Transmutations include alpha, beta, and positron decay that occur as a result of unstable neutron to proton ratios. Artificial Transmutations occurs when a nucleus is bombarded with high energy particles that bring about change.

Artificial Transmutation There are two types of Artificial Transmutaions: Collision of a charged particle with a target nucleus Collision of a neutron with a target nucleus Example: 23692U + 10n 23792U Hint: Natural Transmutation will have a single nuleus going under decay Artificial Transmutation will have two reactants (a fast moving particle and a target material)

Fission and Fusion Fisson: involves the splitting of a heavy nucleus to produce a lighter nuclei Fusion: involves the combining of light nuclei to produce a heavier nucleus. ***In both reactions, total mass of the products is less than the total nuclear mass of reactants.

Conversion of Matter to Energy These reactions do not destroy matter, but they convert it to energy..producing something with less mass. This relationship is expressed by: E=mc2 E= Energy m= Mass c= speed of light

Fission Reaction Fission begins with the capture of a neutron by the nucleus which then becomes unstable. Products include two middle weight nuclei, one or more neutrons, and a large amount of energy. Example: 10n + 23592U 14292Ba + 9136Kr + 10n + energy

Fusion Reactions Fusion reactions involve combining of light nuclei to form heavier ones. Most common example occurs in the sun where Hydrogen can react with large amounts of sun energy. This is not yet available on Earth due to the very high temperatures and pressures needed. The major advantage of Fusion as an energy source if that the products are not highly radioactive, like those of fission reactions.

Half-Life It is impossible to predict when a given unstable nucleus will decay, but the number of unstable nuclei that will decay in a given time in a sample of the element can be predicted. The time it takes for half of the atoms in a given sample of an element to decay is called Half-Life. Each isotope has its own half-life. The shorter the half-life, the less stable it is. Decay values can be found on Table N in your reference table. Example: If X has a half-life of 5s then every 5 seconds will result with half the amount of X than previously present. If there is 20 g of X, after only 5s 10g will be present. Another 5 seconds later, 5 g will be present. The Fraction Remaining will always equal (1/2)n, where n is the number of half lives (found by dividing the total time that the substance has decayed by the half life on table)

Uses of Radioisotopes Dating: Carbon-14 is used to date previously living organisms. While living, organisms use Carbon-14 the same way it uses Carbon-12. When an organism dies it no longer takes in carbon. Using the ½ life of Carbon and how much is present in the organism, the age of the organism can be determined. Chemical Tracers: Radioisotopes can be tracked or “traced”. P-31 can be used to detect phosphorus uptake in plants, while Carbon-14 can trace the pathway of Carbon in metabolic processes Industrial: Radioisotopes can be absorbed at different amounts by different materials. So, they can be used to detect thickness of materials. Medical Applications: Quickly removed from the body and having short half-lives, isotopes can treat disorders such as cancer, participate as tracers in medical diagnosis, and kill bacteria (sterilize).

Radiation Risks While radioisotopes can be used to kill cancerous cells, they have the potential to damage normal tissue and cause severe illness, death, and mutations that could be carried over generations. Radiation Risk Essay!

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