Nuclear Chemistry

Introduction: Lesson 1 -Nuclear chemistry involves the changes in the nucleus. NOTE: Nuclear = radioactive -When the atomic nucleus of one element changes into the nucleus of another element the reaction is called transmutation.

Stability of Nuclei Atoms nuclei contain protons with a positive charge and neutrons with no change. The nucleus of a hydrogen atom contains only protons. We can determine the number of neutrons in an atom by subtracting the atomic number by the atomic mass number. Elements with atomic numbers greater than 83 are called radioactive. To be radioactive means that the nuclei are unstable and are called radioisotopes. To be and isotope of an element both elements have the same number of protons and different number of neutrons. Unstable nuclei decay forming products that are more stable. When it decays, it emits radiation in the form of particles.

Nuclear Radiation There are 4 types of radiation alpha particle- a helium nucleus composed of 2 protons and 2 neutrons beta particle- an electron whose source is an atomic nucleus positron- is identical to an electron but has an opposite charge gamma rays- are similar to X rays but have greater energy Open to Table O – Symbols Used in Nuclear Chemistry Listed here are name, notation, and symbol.

Types of Decay 10. Alpha decay – when an alpha particle is emitted from a nucleus. As particles are emitted, atomic number decreases by 2 and the mass number decreases by 4. Ex; Radium Ra-226 emits an alpha particle it’s atomic # decreases from 88 to 86 and becomes Radon Rn-222. The atomic mass then becomes 222. Draw a diagram of alpha decay.

Beta Decay Beta Decay- When a beta particle is emitted. It is the emission of an electron during the conversion of a neutron to a proton. Ex: Lead Pb-214 decays to bismuth Bi-214 Draw a diagram of Beta Decay.

Positron Emission Positron Emission- Production of a positron during the conversion of a proton to a neutron. Ex: Potassium K- 37 decays to argon Ar- 37

Nuclear Equations Mass and charge must balance on both sides. Mass and energy are conserved always. Ex: N + He  O + H Used to find the missing particle in an equation: Al + n  Na + X

Lesson 2:Nuclear Transmutation Nuclear reactions can be either naturally occurring or artificial. Transmutation: The changing of a nucleus of 1 element into that of a different element. Artificial Transmutation: When change occurs because a nucleus is bombarded w/ high energy particles, such as alpha particles or neutrons. Compare and contrast transmutation and artificial transmutation: Transmutation is natural b/c it’s a result of unstable neutron- to proton ratios. Artificial transmutation happens by bombarding nuclei w/ particles.

2 Types of Transmutations First: Collisions involving a charged particle with an atom’s target nucleus. They must contain enough energy to overcome a proton’s positive charge and repulsive forces. Second: Collisions involving a neutron with an atom’s target nucleus. This is seen in nuclear reactors to generate nuclear electricity.

Fusion and Fission There are two types of nuclear reactions, Fission that produces electricity on Earth and Fusion which occurs in stars. Fission reaction – splitting of a heavy nucleus to produce lighter nuclei Fusion – combine light nuclei to produce heavier nuclei. In these reactions, matter is converted to energy in the equation E=mc^2.

Fission and Fusion con. Since mass is converted into energy, the total mass of the reactants is less than the total mass of the products. The matter that is converted into energy is called the mass defect.

Fission Reactions A fission reaction involves U-235 or Pt-239 and a neutron. A free moving neutron splits the nucleus. The nucleus captures the free moving neutron, becomes unstable and immediately splits. The products in a fission reaction are two middleweight nuclei, one or more neutrons and a large amount of energy.

Lesson 3:Radioactive Decay Decay happens spontaneously and randomly and does not depend on temperature, pressure or concentration. The time it takes for half of the atom in a sample of an element to decay is called the half-life. Each isotope has a half-life located on Table N. Table N also contains information on nuclides, decay mode and nuclide name.

Radioisotopes Many historians use radioisotopes as a way to date archeological artifacts from past living things. This is called carbon dating. C-14 is found in living tissue just like C-12. When an organism dies, no more carbon is taken in. When the C-14 decays the amount left can give an estimate of how old that organism is. Uranium decays to lead over time. Rocks can be dated using a ratio of uranium to lead.

Chemical Tracers Any radioisotope used to follow the path of a material in a system is called a chemical tracer. This method is used to help find radioactive phosphorous to determine fertilizer applications and radioactive carbon in metabolic processes. Radiation can be used to determine the thickness of materials. The thicker the material, the more radiation it absorbs.

Medical Uses Medicine uses radioisotopes for many applications. Tracers are used in medical diagnosis, treatment and removal of bacteria. I-131 treats thyroid conditions Co-60 helps treat cancer by killing cells with gamma radiation. Gamma rays are used to irradiate food, killing bacteria Tc-99 is used to detect cancer cells

Medical Uses con In small doses, radiation has many useful applications but is not without risks. Cancer patients undergoing radiation treatment can become very sick since not only cancer cells are targeted but some normal cells die too. Nuclear power plants produce waste materials with long half-lives. Exposure to high levels of radiation can cause mutations in cells resulting in cancers, birth defects and death.