Would you expect that an anion would be physically closer to the oxygen or to the hydrogens of water molecules that surround it in solution?

Key Concepts

Polarity of Water

Water is a polar molecule, meaning it has a partial positive charge on the hydrogen atoms and a partial negative charge on the oxygen atom. This polarity allows water molecules to interact differently with ions in solution, with the negative end (oxygen) being attracted to positively charged cations and the positive ends (hydrogens) being attracted to negatively charged anions.

Ion-Dipole Interactions

Ion-dipole interactions occur when an ion interacts with the polar molecules of a solvent, such as water. Anions, which carry a negative charge, are attracted to the positive ends of water molecules (the hydrogen atoms), leading to a closer proximity to the hydrogens than to the oxygen atoms in the surrounding water.

Hydration Shell

When an ion is dissolved in water, it becomes surrounded by a layer of water molecules known as a hydration shell. For anions, this shell is formed primarily by water molecules orienting themselves with their hydrogen atoms facing the anion, which stabilizes the ion in solution and affects its behavior and interactions with other species.