Dissociation Theory

[Nicole Gamboa 1G]

Hello! Can someone please explain what dissociation energy is and how you go about finding it? Thank you!

[Amanda Reshke 1D]

I believe dissociation energy is the energy required to break (dissociate) a bond; essentially compounds with more ionic character would be easier to break apart (I usually associate ionic compounds with elements that are far apart on the periodic table- a good example is NaCl), and compounds with more covalent character are harder to break apart because the difference in electronegativity is smaller. Therefore, the energy required to dissociate an ionic bond would be smaller than the energy required to dissociate a covalent bond. I'm not sure about the second part of your question, but does anyone else want to add on?

[Anne Cam 3A]

Dissociation energy is the energy required to break a bond, which is always positive. The shorter the bond, the higher the dissociation energy (because it becomes harder to break shorter/stronger bonds). In the course reader, examples are bonds in F₂, O₂ and N₂, which increase progressively in dissociation energy. This is because large atoms like F have more lone pairs, which cause repulsions and longer bonds (that are easier to break with less dissociation energy). The opposite is true for smaller atoms with less lone pairs and less repulsions.

I checked the textbook and course reader but couldn't find a formula for the dissociation energy, and I recall Dr. Lavelle saying we didn't need to know how to calculate it. There is a table of dissociation energies on page 93 (in the text) for diatomic molecules and page 94 for different bonds. But I did find a formula online, here: https://labs.chem.ucsb.edu/zakarian/armen/11---bonddissociationenergy.pdf which is more complicated and involves enthalpies of the separate atoms minus the enthalpy of the molecule at a specific temperature.