Name:______________________ Date:______________ Chapter 7 Student Guided Notes 7.1 Atomic Theory and Radioactivity General Information Natural background radiation exists all around us. • This radiation consists of __________________________________________ being emitted from a variety of materials. Radioactivity is the release of high energy particles or waves. • Being exposed to radioactive materials can be __________________________. o X-rays, radiation therapy and electricity generation are beneficial. o High energy particles and waves can do damage to DNA in our cells. • When atoms lose high energy particles and waves, ions or even new atoms can be formed. • ____________________________________ are called ________________ when they leave the atom The Electromagnetic Spectrum Invisible Rays Radiation is _____________________, but can be difficult to detect. • _________________________ named X-rays with an “X” 100 years ago because they were previously unknown. • ________________ realized uranium emitted seemingly invisible energy as well. • ____________________ and her husband Pierre named this energy radioactivity. o Early discoveries of radiation relied on photographic equipment • Later, more sophisticated devices such as the ______________________ were developed to more precisely measure radioactivity Radium salts, after being placed on a photographic plate, leave behind the dark traces of radiation. Name:______________________ Date:______________ Isotopes & Mass Numbers ______________________ are different atoms of the ____________________, with the _________________ between the two atoms being the ____________________ in the nucleus. • Isotopes have ________________________________________ - and therefore the same atomic number - as each other. • By having different numbers of neutrons, isotopes have ___________________ ____________________. o Isotopes of an element have the ______________ and same __________ ____________________ Mass number refers to the ___________________________ in an isotope o Atomic mass = proportional average of the mass numbers for all isotopes of an element. 19.9% of boron atoms have 5 neutrons, 80.1% have 6 neutrons 19.9% have a mass number of 10, and 80.1% have a mass number of 11 (.199 * 10) + (.801*11) = 10.8 = atomic mass of boron Representing Isotopes Isotopes are written using standard atomic notation. • ________________________________________________________________. • • Potassium has three isotopes, Potassium is found in nature in a certain ratio of isotopes o ________ is potassium-39, _______ is potassium-40, and _______is potassium-41 o Atomic mass = (____ x 39) + (_____ x 40) + (_____ x 41) = 39.1 Name:______________________ Date:______________ Radioactive Decay Unlike all previously discovered chemical reactions, _________________________ resulted in the formation of completely ___________________. • Radioactivity results from having an unstable nucleus. • When these nuclei ________________________________________________. o Radioactive decay releases energy from the nucleus as radiation. o Radioactive atoms ______ ______________________ __________________, often as different atoms. o An element may have only certain isotopes that are radioactive. These are called _________________ Radioisotope uranium-238 decays in several stages until it finally becomes lead-206 Three Types of Radiation Rutherford identified three types of radiation using an electric field. • Positive ___________________ were attracted to the negative plate. • Negative ___________________were attracted to the positive plate. • Neutral ____________________ did not move towards any plate. Name:______________________ Date:______________ Alpha Radiation _________________________ is a ________________________________ • _______________ charged, and are the most massive of the radiation types. • Alpha particles are essentially the same as a ____________________. • Alpha particles are represented by the symbols . + o Because it has two protons, it has a charge of 2 . o The release of alpha particles is called alpha decay. • Alpha particles are ________ and ______________________________ than the other forms of radiation. A ______________________ will stop an alpha particle Radium-226 releases an alpha particle and becomes Radon-222. Radon has two less protons than radium. Beta Radiation Beta radiation, ___________________________________ . • Negatively charged, and the size of an electron. • Beta particles are represented by the symbols . o Electrons are _____________, so beta particles are assigned a ________________ o Since there is only an electron, a beta particle has a ________________ • Beta decay occurs when a __________________________________ + an electron. o The proton stays in the __________________________________. o It takes a ___________________________ foil to stop a beta particle. Iodine-131 releases a beta particle and becomes Xenon-131. A neutron has turned into a proton + the released electron. Name:______________________ Date:______________ Gamma radiation is a ray of __________________, short-wavelength radiation. • Gamma radiation has _____________________________________________, . • Gamma radiation is the highest energy form of electromagnetic radiation. o It takes thick blocks of lead or concrete to stop gamma rays. • Gamma decay results from energy being released from a high-energy nucleus. • Often, other kinds of radioactive decay will also release gamma radiation. o Uranium-238 decays into an alpha particle and also releases gamma rays. Summary Nuclear equations are written ___________________________, but represent changes in the nucleus of atoms. • Chemical equations represent changes in the position of atoms, not changes to the atoms themselves. 1. _______________________ Name:______________________ Date:______________ _______________________ 2. _______________________ _______________________ 7.2 Half-life General Information It can be difficult to determine the ages of objects by sight alone. • Radioactivity provides a method to _____________________ by measuring _________________________ of remaining radioactive material to stable products formed. Carbon dating measure the ratio of carbon-12 and carbon-14. • Stable carbon-12 and radioactive carbon-14 exist naturally in a constant ratio. o In nature, carbon-12 appears 98.9% of the time, while one carbon-14 atom appears for every 1 trillion normal atoms. • When an organism dies, carbon-14 stops being created and slowly decays. o Measuring the relative amounts of carbon-12 : carbon-14 is called _______________________________________. o Radiocarbon dating only works for organisms less than 50 000 years old The half-life of carbon-14 is ____________________. Rate of Radioactive Decay Half-life measure the rate of radioactive decay. • ________________________ = time required for half of the radioactive sample to decay. • The half life for a radioactive element is a constant rate of decay. • Strontium-90 has a half-life of 29 years. If you have ___________ of strontium-90 today, there will be ___________ remaining in _____ years. Name:______________________ Date:______________ Decay curves show the rate of decay for radioactive elements. • The curve shows the relationship between half-life and percentage of original substance remaining. Common Isotope Pairs There are many radioisotopes that can be used for dating. • ______________ = ________________________________________________. • _______________ = _______________________________________________. • The rate of decay remains constant, but some elements require one step to decay, while others decay over many steps before reaching a stable daughter isotope. o ____________ decays into _____________ in one step o Uranium-235 decays into lead-207 in fifteen steps. o Thorium-235 decays into lead-208 in ten steps. Potassium 40 Radioisotopes with very long half-lives can help determine the age of very old things. • The potassium-40/argon-40 clock has a half-life of ________________________. • Argon-40 produced by the decay of potassium-40 becomes trapped in rock. • Ratio of potassium-40 : argon-40 shows ________________________. Name:______________________ Date:______________ 7.3 Nuclear Reactions General Information Nuclear _______________ and_____________________ are processes that involve extremely large amounts of energy. • Fission = ____________________________________ • Fusion = __________________________ _________________________________ Nuclear power plants can generate large amounts of electricity through Nuclear fission. • In Canada, Ontario, Quebec and New Brunswick currently use nuclear power. • Canadian-made nuclear reactors are called CANDU reactors. • CANDU reactors are considered safe and effective, and are sold throughout the world. The Bruce Nuclear Generating Station on the shores of Lake Huron, in Ontario Nuclear Fission Nuclear energy used to ____________________ comes from ________________. • Nuclear fission is the______________ of one heavy nucleus into ___________________ smaller nuclei, as well as some sub-atomic particles and _______________. • A heavy nucleus is usually unstable, due to many + protons pushing apart. • When fission occurs: 1. ._________________________________. 2. __________________________________. Nuclear reactions are _________________________ chemical reactions. • In chemical reactions, mass is conserved, energy changes are relatively small. o There are no changes to the nuclei in chemical reactions • In nuclear reactions, ____________________________________________. o Protons, neutrons, electrons and/or gamma rays can be lost or gained. o _____________________ = ____________________________ Nuclear Equations Natural radioactive decay consists of the release of alpha, beta and gamma radiation. Name:______________________ • • • • Date:______________ Scientists can also force ( = induce) nuclear reactions by smashing nuclei with alpha, beta and gamma radiation. The rules for writing these equations are the same as earlier nuclear equations _________________________________ ______________ of the equation Charges must equal on both sides of the equation Fission of Uranium 235 It is much easier to crash neutral neutron than a positive proton into a nucleus to release energy. • Most nuclear fission reactors and weapons use this principle. • ________________, , crashes into an atom of _____________________ to create unstable _________________, which then undergoes radioactive decay. After several steps, atoms of krypton and barium are formed, along with the release of 3 neutrons and huge quantities of energy. The induced nuclear fission of uranium-235. This nuclear reaction is the origin of nuclear power and nuclear bombs. Chain Reactions Once the nuclear fission reaction has started, it can keep going. • The ____________released in the induced reaction can then _______________________ on other uranium-235 atoms. Name:______________________ • • • Date:______________ This __________________ can quickly get out of control o Fermi realized that materials that could absorb some neutrons could help to control the chain reaction. Nuclear reactors have complex systems to ensure the _____________________________________________. An uncontrolled chain reaction can result in the release of excess energy of harmful radiation o It is on this concept that nuclear bombs are created. CANDU Reactions Canada’s nuclear research into the safe use of nuclear reactions has resulted in the creation of ______________________________. • CANDU rectors are found in various countries around the world. o Canada, South Korea, China, India, Argentina, Romania and Pakistan • The reactors are known to be safe and easy to shut down in an emergency. o _______________________________________________________ turbines. Hazardous wastes produced by nuclear reactions are problematic. • Some waste products, like __________, can be re-used • Some products are very radioactive, however, and must be stored away from living things. o Most of _______________________ _____________________________ o It takes 20 half-lives _____________ _____________________________ Nuclear Fusion _____________ = _________________________ ____________________________ • __________________________________, two hydrogen nuclei join under tremendous heat and pressure to form a helium nucleus. • When the helium atom is formed, __________________ of energy are released. Scientists cannot yet find a safe, manageable method to harness the energy of nuclear fusion. • So-called “cold fusion” would occur at temperatures and pressures that could not be controlled. Name:______________________ Date:______________
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