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Unit 3 What is an isotope? Atoms of the same element can have different numbers of neutrons; the different possible versions of each element are called isotopes. For example, the most common isotope of hydrogen has no neutrons. There is another version of hydrogen with 1 neutron, and another version with 2 neutrons. Hydrogen-1 Hydrogen-2 Hydrogen - 3 What makes one isotope different from another isotope? __________________________________ Symbols for Isotopes I Do: Write the isotope symbol and name for an atom with 42 protons, 40 electrons, and 54 neutrons Symbol______Name__________________ We Do: Write the isotope symbol and name for an atom with 42 protons, 42 electrons, and 58 neutrons Symbol______Name________________________ You Do: Write the isotope symbol and name for an atom with 50 protons, 50 electrons, and 62 neutrons Symbol______Name________________________ How many isotopes can one element have? Can an atom have just any number of neutrons? There ARE "preferred" combinations of neutrons and protons – Light elements tend to have about as many neutrons as protons – Heavy elements apparently need more neutrons than protons in order to stick together. – Atoms with a few too many neutrons, or not quite enough, can sometimes exist for a while, but they're unstable. How many isotopes can one element have? Can an atom have just any number of neutrons? • Do atoms just fall apart if they don't have the right number of neutrons? – YES! Unstable atoms are radioactive: their nuclei change or decay by spitting out radiation, in the form of particles or electromagnetic waves. Common Uses for Isotopes Smoke detectors - Many contain a small amount of americium-241. By utilizing the radioactive properties of this material, smoke from a fire can be detected at a very early stage. Common Uses for Isotopes Radioactive dating - If the half life of a given isotope (usually Carbon-14) is known, the amount of that isotope and the product of its decay can be analyzed to determine the age of once-living organisms Example : If an organism such as a tree contained 1 gram of carbon-14 while it was living, then after 5700 years it would contain half that amount, or 0.5 grams of carbon-14. Common Uses for Isotopes Medicine - Radioactive isotopes can be injected into a patient’s body. These isotopes will then appear on a scan and can help doctors diagnose problems or disease Common Uses for Isotopes Nuclear Energy - Radioactive elements such as uranium can be utilized to create energy through fission (splitting apart). Average Atomic Mass Listed on the periodic table • Is a weighted average of all the isotopes for that element. • This is why atomic mass is not a whole number. Steps for Determining Average Atomic Weights 1. 2. 3. 4. Turn the percent into a decimal. Multiply the decimal by the mass. Repeat for each isotope Add the masses up. Example: Magnesium Isotopes Mass of Isotope Percent Abundance Mg-24 = 24.0 amu 78.70% = _____________ Mg-25 = 25.0 amu 10.13% = _____________ Mg-26 = 26.0 amu 11.17% = _____________ Atomic mass (average mass) Mg= ___________ amu