M4 The Periodic Table - Lecture notes 6-8 PDF

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Module 4: The Periodic Table Some Element Factoids  Elements in their “elemental” form are neutral (#protons = #electrons)  Most elements are NOT found in their “elemental” forms in nature  When found in their “elemental” form, they are unlikely to be “pure”  An element’s symbol can stand for: o The element itself o One atom of the element o A particular quantity of the element (mole) Mendeleev!  1869: Dimitri Mendeleev published the first systematic ordering of the elements known at the time with respect to both mass and chemical properties. Others had published similar systems around the same time, but only Mendeleev left deliberate blanks in his table AND predicted the properties of these missing elements The Periodic Table of the Elements  Mendeleev: arranged the elements in increasing atomic weights o Saw repeating patterns of properties  Modern: Elements arranged in order of increasing Atomic Number (#protons) o Repeating patterns of properties still there  Rows are called “Periods” o Periods show regular variations in atomic and chemical properties. These properties repeat themselves row to row o The rows (or Periods) correspond to the main energy shells (n shells)  Columns are called “Groups” o Elements in the same Group often show very similar chemical behavior. Groups are sometimes called “Chemical Families” Metals – Left Side of Table  Most Elements are metallic o Past Uranium (92) are man-made  Uses: LOTS! Non-metals: Right Side of Table (+ Hydrogen!)  Only 17 non-metals  H, C, N, O most important for life Semi-Metals  Semi-Metals or Metalloids have properties intermediate between metals and nonmetals  Most important here are the semiconductors: Si, Ge, and As Special Names for Special Groups  Main Group or Representative Elements Groups 1, 2, 13-18 (A groups) o All non-metals o All semi-metals o Contains metals with predictable chemistry

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Group 1(IA): Alkali Metals o Soft, silvery metals o Low densities o Excellent conductors o Highly reactive with air and water o Never found free in nature  Lithium, sodium, potassium, rubidium, cesium, francium Group 2: Alkaline Earth Metals o Brittle, silver metals o Low densities o Excellent conductors o Heavier members are reactive with air and water o Never found free in nature  Beryllium, magnesium, calcium, strontium, barium, radium Halogens: Group 17 (7A) o All exist as diatomic units as elements o All very reactive o Never found free in nature  Fluorine, chlorine, bromine, iodine, astatine The Noble Gases: Group 18 (8A) o Very unreactive o Only heaviest (Kr, Xe) can be forced to make compounds o End each Period of the Table o Emit colored light when electrically excited – “neon lights” o Rn – radioactive; produced from uranium decay  Helium, neon, argon, krypton, xenon, radon The Transition Metals Groups 3-13 (B groups) o Chemistry more varied and complex than Main Group metals o Known for forming highly colored complexes o Structural Metals: Ti, Fe, Ni, Cr, Mo o Coinage Metals: Cu, Ag, Au, (Pt) o Biological Importance:  Fe – hemoglobin  Many others – enzymes...