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THE PERIODIC TABLE AP CHEMISTRY 2010-2011 Ms. Paskowski History of the Periodic Table Many early scientists organized the elements in a table. Mendeleev organized the elements according to physical and chemical properties. Correctly predicted the existence of previously undiscovered elements and their properties Figure 7.24 Mendeleev's Early Periodic Table, Published in 1872 Periodic Trends Ionization Energy Electron Affinity Atomic Radius Ionic Size Valence Electrons 7.12 Ionization Energy Energy required to remove an electron from a gaseous atom or ion. In general, as we go across a period from left to right, the first ionization energy increases. In general, as we go down a group from top to bottom, the first ionization energy decreases. 7.12 Ionization Energy Why does the IE decrease down a group? Why does the IE increase across a period? The effective nuclear charge increases across a period and decreases down a column. What is effective nuclear charge? The Values of First Ionization Energy for the Elements in the First Six Periods 7.12 Concept Check Explain why the graph of ionization energy versus atomic number (across a row) is not linear. Where are the exceptions? 7.12 Concept Check Which atom would require more energy to remove an electron? Why? Li Cs 7.12 Concept Check Which has the larger second ionization energy? Why? Lithium or Beryllium 7.12 Successive Ionization Energies (KJ per Mole) for the Elements in Period 3 7.12 Electron Affinity Energy change associated with the addition of an electron to a gaseous atom. In general as we go across a period from left to right, the electron affinities become more negative. In general electron affinity becomes more positive in going down a group. 7.12 Figure 7.32 The Electron Affinity Values for Atoms Among the First 20 Elements that Form Stable, Isolated X- Ions Atomic Radius In general as we go across a period from left to right, the atomic radius decreases. In general atomic radius increases in going down a group. 7.12 Figure 7.33 The Radious of an Atom (r) is Defined as Half the Distance Between the Nuclei in a Molecule Consisting of Identical Atoms Concept Check Which should be the larger atom? Why? Na Cl 7.12 Concept Check Which is larger? The hydrogen 1s orbital The lithium 1s orbital Which is lower in energy? The hydrogen 1s orbital The lithium 1s orbital 7.12 Atomic Radius of a Metal 7.12 Atomic Radius of a Nonmetal 7.12 Atomic Radii for Selected Atoms Exercise Arrange the elements oxygen, fluorine, and sulfur according to increasing: Ionization energy Atomic size 7.12 Final Thoughts It is the number of valence electrons that chemists use to explain an atom’s chemistry. BUT do not forget the involvement of the nucleus. Electrostatic interaction of positive and negative charges is the fundamental force that explains chemical interactions. i.e., the nucleus of one atom MUST attract the electrons of another atom to create a chemical bond . . . 7.13