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The Periodic Table Ms. Pollock Physical Science 2008-2009 Organizing the Elements • Dmitri Mendeleev’s periodic table published in 1869 in Russia • Born in Siberia in 1834 • Chemistry professor at University of St. Petersburg • Wrote textbook for students; led to development of periodic table • Extremely accurate periodic table for time Dmitri Ivanovich Mendeleev • http://www.aip.org/hist ory/curie/periodic.htm Mendeleev’s Table • Just over 60 elements identified at the time • Organized by atomic weights (masses) and found that the properties of elements repeated periodically • Not all elements known, so some spaces left blank • Accurately predicted properties of elements not yet discovered Mendeleev’s Table Improving the Periodic Table • Henry Moseley, 1913 • Found that some elements did not line up perfectly in Mendeleev’s table • Re-ordered elements by atomic number, rather than atomic mass • British; studied with Ernest Rutherford • Killed in World War I Henry Moseley • http://www.chemistry.co .nz/henry_moseley.htm The Atom and the Periodic Table • Elements sorted according to properties • Groups – vertical columns; similar properties – Same group = electrons in same energy level – Electrons in same energy level = similar chemical properties and behavior • Periods – horizontal rows – Each row a new energy level – Row 1 = 1 energy level – Row 7 = 7 energy levels The Atom and the Periodic Table Electron Dot Diagrams • Elements in same group have the same number of electrons in their outer energy levels. • The outer energy level can be drawn using an electron dot diagram. • The symbol of the element and a series of dots are used to represent electrons in the outer energy levels. • Developed by American chemist G. N. Lewis Electron Dot Diagrams • http://www.ausetute.com.au/lewisstr.html • Write the symbol first. • Then, place one electron at each side of the symbol. • Finally, pair electrons until all valence (outer shell) electrons are accounted for. Electron Dot Diagrams Cl Group 17: Valence electrons cannot exceed 8 (octet rule), so take the group number (17) and subtract 10. 17 – 10 = 7 valence electrons Electron Dot Diagrams Cl Electron Dot Diagrams Cl Electron Dot Diagrams Cl Electron Dot Diagrams Cl Electron Dot Diagrams Cl Electron Dot Diagrams Cl Electron Dot Diagrams Cl Regions on the Periodic Table • Several areas on periodic table with specific names • Left = metals (mostly solids) • Right = nonmetals (mostly gases) • Zig-zag line = metalloids • Extra rows = Lanthanides and Actinides Periodic Table Regions (Metals) http://www.dkimages.com/discover/previews/796/939317.JPG Periodic Table Regions (Nonmetals) Periodic Table Regions (Metalloids) katie-maggie-mettaloids-g.wikispaces.com Elements in the Universe • Modern technology making elements in other parts of universe easy to identify • Hydrogen and helium thought building blocks of other elements • Many elements found only in stars or as a result of the decay of other elements http://images.iop.org/objects/physicsweb/world/16/7/3/pwpia1_07-03.jpg