ch910 1_Part2 - GENERAL CHEMISTRY CHAPTER 9 & CHAPTER...

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GENERAL CHEMISTRY PAGE 5 OF 22 Trend in Lattice Energy – Ion Size By Coulomb’s Law, lattice energies are largest when the distance r, between ions is small E POTENTIAL = (2.31 x 10 19 J. nm) ? 1 ? 2 ± A small distance (r) means the ions are close together = small ionic radii The potential energy (forces of attraction) between ions is stronger (less distance) If Q 1 and Q 2 are constant, the largest lattice energies are for compounds formed from the smallest ions For ionic compounds that have the same anion but different cations , lattice energy increases as the cation becomes smaller As the distance between the ions gets larger, the ions cannot get as close together, and do not release as much energy when the lattice forms Example : K + > Na + > Li + Lattice Energies: LiF > NaF > KF (KF has the least exothermic lattice energy) For ionic compounds that have the same cation but different anions , lattice energy increases as anion size decreases The more electrons an atom has, the more electron-electron repulsions, the bigger the anion The bigger the anion, the greater the distance between the cation & anion, the smaller and less exothermic the lattice energy Example : I - > Br - > Cl - > F - Lattice Energies: LiF > LiCl > LiBr > LiI Trend in Lattice Energy – Ion Charge The force of attraction between oppositely charged particles is proportional to the product of Q 1 and Q 2 The larger charge of the ions the stronger the forces of attraction Stronger forces of attraction = larger the lattice energy Between ion size and ion charge, the ion charge is generally more important and affects the lattice energy
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ch910 1_Part2 - GENERAL CHEMISTRY CHAPTER 9 & CHAPTER...

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