General chemistryLesson 5 of 6 in the course Chemical Bonding and Molecular Geometry

Covalent Bond Energies, Ionic Lattice Energies, and Born–Haber Cycles

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

Covalent bonds hold atoms together in molecules. In this lesson, we define how their strength is measured and examine how bond order and bond length relate to strength.

A covalent bond’s strength describes how much energy is needed to separate its bonded atoms. Breaking a bond requires energy, so the process is endothermic. The stronger the bond, the more energy is required to break it.

All flashcards

Bond energy
The energy required to break one mole of a specified covalent bond in gaseous molecules.
Average bond energy
An average value across molecular environments that may differ from the energy for one particular bond.
Lattice energy, separation convention
The energy required to separate one mole of an ionic solid into gaseous ions.
Born–Haber cycle
A Hess’s law cycle that relates ionic-solid formation to steps involving gaseous atoms and ions.
Bond-energy reaction estimate
The sum of energies for bonds broken minus the sum for bonds formed.

Quiz questions

  1. When a reaction enthalpy estimate from bond energies is negative, what does the sign indicate?Answer: The reaction is exothermic and releases heat.
  2. Using the convention that defines lattice energy as the energy needed to separate an ionic solid, what does the value describe?Answer: Separating one mole of the solid into gaseous ions.
  3. Which pair of factors generally increases the lattice energy magnitude of an ionic solid?Answer: Greater ionic charges and shorter interionic distances.
  4. In a Born–Haber cycle using the separation convention for lattice energy, what enthalpy term represents lattice formation?Answer: The negative of the lattice energy.
  5. Why are lattice-energy values and covalent bond dissociation energies not direct one-to-one measures of bond strength?Answer: They describe different interactions and particle scales.

Based on Chemistry 2e by Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson, PhD (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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