Intermolecular Forces In Solutions

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This post will focus on the interactions between solute and solvent particles (ions and molecules).  When we have these solute-solvent interactions, we say that the solute has become solvated.  A solvated solute molecule is completely surrounded and "carried" by solvent molecules.  The solvation process is involved in the formation of a solution (in the very act of the solute dissolving to create a solution!).  In order for a solute to dissolve or disperse, in the case of a liquid solute,  the sum total of solute-solvent interactions must be stronger than the total pure solute bond energies.

Types of Solvent-Solute Interactions

There are three main types of solvent-solute interactions; (1) dipole-dipole, (2) dipole-ion, and (3) London Dispersion Forces.  The first two types are a polar form of interaction and the third type is a nonpolar form of interaction.

The polar and ion interactions are for substances like water and sodium chloride.  London dispersion forces dominate in compounds like the hydrocarbons, such as octane (An eight carbon single bonded chain surrounded by hydrogen atoms).  The following presentation and drawing depict the water solution polar interactions described above.

The interactions depicted above and dominating London Dispersion Forces (Hydrophobic Interactions, not shown) occur because, in every case the solute and solvent are similar (has similar electrical properties).  This is why the general rule of thumb for determining if a solute will dissolve in a particular solvent is "like dissolves like".

This Concludes this section (label) of Learning Chemistry Easily.

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