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1.3 Understanding Atomic Mass A Review: Subatomic particles Name Symbol Relative Charge mass Actual mass (g) Electron e- -1 1/1840 9.11 x 10-28 Proton p+ +1 1 1.67 x 10-24 Neutron no 0 1 1.67 x 10-24 http://www.unit5.org/christjs/site%20map.htm Structure of the Atom There are two regions: 1. The Nucleus: • With protons and neutrons • Positive charge • Almost all the mass 2. Electron cloud • Most of the volume of an atom • The region where the electrons can be found http://www.unit5.org/christjs/site%20map.htm http://www.andrew.cmu.edu/user/jgrao/Manchester%20United/giant%20stadium.jpg If the atom was the size of a stadium, the nucleus would be the size of: a marble. http://www.akronmarbles.com/marble-frag-2.jpg Standard Atomic Notation Includes the symbol of the element, the mass number and the atomic number # protons + # neutrons mass number # protons Mass number Atomic number X http://www.unit5.org/christjs/site%20map.htm http://chemistry.beloit.edu/Stars/EMSpectrum/fluorine.gif • Find the – number of protons = 9 + – number of neutrons = 10 – number of electrons = 9 – Atomic number = 9 – Mass number = 19 19 9 F http://www.unit5.org/christjs/site%20map.htm Find the – number of protons = 35 – number of neutrons = 45 – number of electrons = 35 – Atomic number = 35 – Mass number = 80 80 35 Br http://www.unit5.org/christjs/site%20map.htm Find the – number of protons = 11 – number of neutrons = 12 – number of electrons = 10 – Atomic number = 11 – Mass number = 23 23 11 1+ Na Sodium ion http://www.unit5.org/christjs/site%20map.htm http://www.webelements.com/webelements/elements/media/nearingzero/Na.gif http://discover.edventures.com/images/termlib/i/isotope/support.gif Isotopes • Atoms of the same element can have different numbers of neutrons This gives them different mass numbers. They have the same atomic numbers. They look, act and react the same. C-12 vs. C-14 Isotopes of Hydrogen • Protium (H-1) 1 proton, 0 neutrons, 1 electron Most abundant isotope • Deuterium (H-2) 1 proton, 1 neutron, 1 electron Used in “heavy water” • Tritium (H-3) 1 proton, 2 neutrons, 1 electron radioactive Naming Isotopes • Put the mass number after the name of the element • Examples: • Carbon-12 and Carbon-14 • Uranium-235 and Uranium-238 Isotopes of Three Common Elements Mass Element Carbon Chlorine Silicon Symbol Mass (amu) Fractional Abundance Number 12 6 C 12 12 (exactly) 99.89% 13 6 C 13 13.003 1.11% 35 17 Cl 35 34.969 75.53% 37 17 Cl 37 36.966 24.47% 28 29 30 27.977 28.976 29.974 28 14 29 14 Si Si 30 Si 14 LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World , 1996, page 110 92.21% 4.70% 3.09% Average Atomic Mass 12.01 35.45 28.09 Which isotopes are represented in this sketch? http://discover.edventures.com/images/termlib/i/isotope/support.gif Calculations of Average Atomic Mass Why is the mass number on a periodic table never a nice whole number? Mass Number vs AverageAtomic Mass • The Mass Number is specific to one isotope. • The Average Atomic Mass is the calculated based on the abundance of each naturally occurring isotope of that element. • The Average Atomic Mass is shown on Periodic Tables. Average Atomic Mass • How heavy is an atom of oxygen? • There are different kinds of oxygen atoms. oxygen-16, oxygen-17 and oxygen-18 • We are more concerned with average atomic mass, based on the abundance of each element in nature. • We don’t use grams because the numbers would be too small. California WEB http://www.unit5.org/christjs/site%20map.htm http://www.unit5.org/christjs/site%20map.htm Atomic Mass Unit (amu or u) • This unit is used instead of grams. • It is 1/12 of the mass of a carbon-12 atom. Radioactive Isotopes • Radioactive: – Capable of spontaneously emitting radiation in the form of particles and/or gamma rays • Radioisotope: – A radioactive isotope of an element that occurs naturally or is produced artificially. Radioisotopes • Many elements have one or more isotopes that are unstable. • Atoms of unstable isotopes decay, emitting radiation as their nucleus changes. • The changes can happen quickly or slowly, depending on the isotope. • Radiation emitted can be harmless or very dangerous to living cells. Applications of Nuclear Science Anthropology: Radiology: Nuclear Reactors: http://www.johnharveyphoto.com/RoadTrip/NuclearReactor.jpg Radioisotopes • Radioactive isotopes • Many uses – Medical diagnostics – Optimal composition of fertilizers – Abrasion studies in engines and tires Radioisotope is injected into the bloodstream to observe circulation. http://www.unit5.org/christjs/site%20map.htm