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I am still a little confused on the explanation for why the energies where negative when Dr. Lavelle was talking about the interactions between ions and molecules. He said it was because energy is released? I am not completely sure; I thought the interaction between the ions as they come together would require energy, which makes it negative. Can someone clarify?
In terms of thermodynamics, if you think about the molecule/compound as a system, anything that increases the energy of the system, for example putting in energy to break bonds, makes delta E positive. When energy is released, delta E is negative. The intermolecular/interionic interactions have negative energy because they are favorable interactions that lower the energy of the system. For example, the electrostatic attraction between Na+ and Cl- makes it more energetically favorable for them to form an ion-ion interaction (ionic bond); NaCl is more stable than Na+ and Cl- separately, which lowers the energy of the system. Therefore, the energies are negative. Hope this helps!
Negative energies imply that energy is given off by what is taking place. In this case, the more negative energy forces for ion-ion attractions and hydrogen bonds are more favorable and give off more energy than dipole-dipole and dipole induced-dipole. The reverse is true that a greater energy must be input to break an ion-ion and hydrogen bond than dipole-dipole or dipole induced-dipoles. But since we are concerned with the formations of these bonds and attractions, the energy will be negative because it is an output of the attractions.
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