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AP Chemistry Unit 4 – Molecular Structure

AP Chemistry Unit 4 – Molecular Structure. Lesson 2 – Ionic Bonding Book Section: 8.2. Energetics of Ionic Bonding. As we saw in the last unit, it takes 495 kJ/mol to remove electrons from sodium. Energetics of Ionic Bonding. We get 349 kJ/mol back by giving electrons to chlorine.

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AP Chemistry Unit 4 – Molecular Structure

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  1. AP ChemistryUnit 4 – Molecular Structure Lesson 2 – Ionic Bonding Book Section: 8.2

  2. Energetics of Ionic Bonding • As we saw in the last unit, it takes 495 kJ/mol to remove electrons from sodium.

  3. Energetics of Ionic Bonding • We get 349 kJ/mol back by giving electrons to chlorine.

  4. Energetics of Ionic Bonding • But these numbers don’t explain why the reaction of sodium metal and chlorine gas to form sodium chloride is so exothermic! • VIDEO

  5. Energetics of Ionic Bonding • There must be a third piece to the puzzle. • What is yet unaccounted for is the electrostatic attraction between the newly-formed sodium cation and chloride anion.

  6. Lattice Energy • This third piece of the puzzle is the lattice energy. • The energy required to completely separate a mole of a solid ionic compound into its gaseous ions. • The energy associated with electrostatic interactions is governed by Coulomb’s Law:

  7. Lattice Energy • Lattice energy, then, increases with the charge on theions. • It also increaseswith decreasingsize of ions.

  8. Lattice Energy • Arrange the following ionic compounds in order of increasing lattice energy: • NaF, CsI, CaO

  9. Lattice Energy • Arrange the following ionic compounds in order of increasing lattice energy: • NaF, CsI, CaO • CsI < NaF < CaO

  10. Energetics of Ionic Bonding • By accounting for all three energies (ionization energy, electron affinity, and lattice energy), we can get a good idea of the energetics involved in such a process.

  11. Energetics of Ionic Bonding • These phenomenaalso helps explainthe “octet rule.” • Metals, for instance, tend to stop losing electrons once they attain a noble gas configuration because energy would be expended that cannot be overcome by lattice energies.

  12. Octet Rule • Predict the ion generally formed by Sr, S, and Al

  13. Octet Rule • Predict the ion generally formed by Sr, S, and Al. • Sr2+ • S2- • Al3+

  14. Homework: 8.14, 8.16, 8.18, 8.20, 8.22, 8.24, 8.28 • This week: • Friday: Lewis Structures for Molecular Compounds (8.3-8.5, 8.7), End of 1st Quarter

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