# Controlled dissolution of a single ion from a salt interface

## TL;DR

The study shows how a single water molecule can selectively dissolve an anion from a salt surface, offering insights into ion-water interactions at the atomic level.

## Contribution

The paper demonstrates controlled manipulation of a single water molecule to observe anion dissolution at a salt interface.

## Key findings

- A single water molecule can polarize an anion in a NaCl crystal, weakening ionic bonds.
- Selective dissolution of anions is driven by strong anion-water interactions at the interface.
- The process reveals an elementary step in single-ion chemistry with implications for ion-related technologies.

## Abstract

Interactions between monatomic ions and water molecules are fundamental to understanding the hydration of complex polyatomic ions and ionic process. Among the simplest and well-established ion-related reactions is dissolution of salt in water, which is an endothermic process requiring an increase in entropy. Extensive efforts have been made to date; however, most studies at single-ion level have been limited to theoretical approaches. Here, we demonstrate the salt dissolution process by manipulating a single water molecule at an under-coordinated site of a sodium chloride film. Manipulation of molecule in a controlled manner enables us to understand ion–water interaction as well as dynamics of water molecules at NaCl interfaces, which are responsible for the selective dissolution of anions. The water dipole polarizes the anion in the NaCl ionic crystal, resulting in strong anion–water interaction and weakening of the ionic bonds. Our results provide insights into a simple but important elementary step of the single-ion chemistry, which may be useful in ion-related sciences and technologies.

The strong ionic bond in salt is broken by electrostatic interactions with water, but direct observation at the level of a single ion is challenging. Here, the authors have visualized the preferential dissolution of an anion by manipulating a single water molecule.