Why does sodium chloride dissolve in water?

Sodium chloride dissolves in water due to the polar nature of water molecules and ion-dipole interactions.

Sodium chloride, commonly known as table salt, is an ionic compound. This means it is composed of positively charged sodium ions (Na+) and negatively charged chloride ions (Cl-). When sodium chloride comes into contact with water, the polar water molecules interact with the ions in the salt, causing it to dissolve.

Water is a polar molecule, meaning it has a positive end and a negative end. This is due to the difference in electronegativity between the oxygen atom and the hydrogen atoms in the water molecule. The oxygen atom attracts the shared electrons more strongly, making it slightly negative, while the hydrogen atoms become slightly positive. This polarity allows water to dissolve many substances, including ionic compounds like sodium chloride.

When sodium chloride is added to water, the positive end of the water molecules are attracted to the chloride ions, and the negative end of the water molecules are attracted to the sodium ions. This attraction is known as ion-dipole interaction. The water molecules surround the individual ions, pulling them away from the crystal lattice structure of the solid salt. This process is known as solvation or hydration when the solvent is water.

The energy required to break the ionic bonds in the sodium chloride crystal is compensated by the energy released when the ions form new bonds with the water molecules. This makes the process energetically favourable, allowing the sodium chloride to dissolve. The dissolved ions remain in the solution, surrounded by water molecules, which prevents them from rejoining and forming a solid again.

In summary, the dissolution of sodium chloride in water is a result of the polar nature of water and the ion-dipole interactions between the water molecules and the ions in the salt. This process is energetically favourable, leading to the complete dissolution of the salt in the water.