Question

What does it mean to say that ions are hydrated when an ionic substance dissolves in water?

Short answer

When an ionic substance dissolves in water, the ions present in the substance are surrounded by water molecules, forming a solvation shell, due to water's polar nature. This process separates the ions from the crystal lattice, creating stable hydrated ions that can dissolve in water.

Step-by-step solution

Understanding Ions

An ion is an atom or a group of atoms that have an electric charge, either positive or negative, due to the gain or loss of one or more electrons. In an ionic substance, the ions are arranged in a regular repeating pattern called a crystal lattice. Positive ions are called cations, and negative ions are called anions.

Understanding Water's Polar Nature

Water is a polar molecule, meaning it has distinct regions of positive and negative charges. This property results from the difference in electronegativity between the oxygen and hydrogen atoms, leading to a dipole moment with a partial positive charge on each of the hydrogen atoms and a partial negative charge on the oxygen atom.

Understanding the Hydration Process

When an ionic substance dissolves in water, the water molecules surround the ions in the lattice, effectively separating them from the crystal structure. This process is called hydration. The partial negative charge on the oxygen atom of a water molecule attracts the positive ions (cations), while the partial positive charge on the hydrogen atoms attracts the negative ions (anions).

Formation of Hydrated Ions

As the water molecules surround the ions, they form multiple bonds with the ion, leading to the formation of a shell or a "solvation shell" around the ion. This new structure has the ion at its core and is surrounded by water molecules – it is called a hydrated ion. The hydrated ion is more stable than the original ion due to the interactions with the water molecules.

Explanation of "Ions are Hydrated"

To say that ions are hydrated when an ionic substance dissolves in water means that the ions of the substance are surrounded by water molecules, forming a solvation shell that allows the ions to be separated from the crystal lattice and dissolve in water. This process is essential for the solubility of ionic substances in water and has many practical applications in various fields, such as chemistry, environmental science, and medicine.