CHEM151Chapter 6

Chemistry (MasteringChemistry Series)

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9/23/2008 1 Chapter 6 Ionic Bonds Ionic Bonds and Periodic and Periodic Trends Trends Electron Configurations of Ions y Anions : simply continue to add electrons in the Aufbau order y Write the electron configuration of: y F - y O 2- y N 3- y These ions are called isoelectronic . Ions form the same electron configuration as another element 2 Electron Configurations of Ions y Cations : remove electrons in the reverse of the Aufbau order y Write the electron configuration of: y Al 3+ y Mg 2+ y Na + y These ions are also isoelectronic . 3
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9/23/2008 2 Electron Configurations of Ions y Transition metal cations: remove electrons from the s orbital first, then in the reverse Aufbau order y Write the electron configurations for: y Cr 2+ y Ti 3+ y Fe 3+ 4 More Examples y Write electron configurations for the following atoms/ions. y K (long-hand) y S 2- (long-hand) y Ni (short-hand) y Mg 2+ (long-hand) y Fe 2+ (short-hand) 5 Categories of Electrons y Inner (core) electrons – those seen in the previous noble gas – energy level completely filled y Outer Electrons – those in highest energy level – farthest from the nucleus y Valence Electrons – those involved in forming compounds Transition metals – d’s can count in valence
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9/23/2008 3 Shielding y Repulsion from other electrons Inner electrons shield the nucleus effect on outer electrons – thus reducing the full nuclear charge Effective Nuclear Charge y Electrons in inner shells shield protons’ pull on electrons in the outer shell Reduce attractive forces of outer (valence) electrons. Th Eff ti N l Ch (Z ) i th y The Effective Nuclear Charge eff ) is the amount of positive charge on the nucleus that is actually perceived by an outer electron. In a row (or period) in the Periodic Table, the number of protons increase, but the number of inner e - ’s (shielding e - ’s) stay the same. 8 Atomic Radius y Atomic radius can be predicted by looking at element’s # of electrons y Definition: one-half the distance between two nucleitwo adjacent atoms 9
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9/23/2008 4 Atomic Atomic Radii Radii 10 y Which element in each pair has a larger atomic radius? Why? y F or Cl Trends in Atomic Radius y C or N y Rb or Ca y Na or Mg y K or Na 11 Ionic Ionic Radii Radii vs. Atomic vs. Atomic Radii Radii y Cations are smaller than their parent atoms Electrons removed = less electron repulsion (shielding) y Anions are larger than their parent atoms Electrons added = more electron repulsion (shielding)
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9/23/2008 5 Ionic Radius y Radius of cation or anion Trends in Ionic Trends in Ionic Radii Radii - Cations Cations 14 Figure 8.9 Trends in Ionic Trends in Ionic Radii Radii - Anions Anions
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9/23/2008 6 Trends in Ionic Radii Trends in Ionic Radii Z eff for Isoelectronic Series y In an isoelectronic series - all ions have the same number of electrons y Z eff increases from most negative to most positive ion.
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