2- Hydrate

It is a result of the hydrogen bond that water can form hydrates. The hydrogen bond causes the water molecules to align in regular orientations. The presence of certain compounds causes the aligned molecules to stabilize and a solid mixture precipitates.

The water molecules are referred to as the “host” molecules, and the other compounds, which stabilize the crystal, are called the “guest” molecules, the guest molecules are more often referred to as “formers.” The hydrate crystals have complex, three-dimensional structures where the water
molecules form a cage and the guest molecules are entrapped in the cages.

Hydrate

1- Introduction

In its most general sense, a hydrate is a compound containing water. For example, there is a class of inorganic compounds called “solid hydrates,” ionic solids where the ions are surrounded by water molecules and form crystalline solids. hydrates are composed of a small molecule and water.

Hydrates are crystalline solid compounds formed from water and smaller molecules. They are a subset of compounds known as clathrates or inclusion compounds. A clathrate compound is one in which a molecule of one substance is enclosed in a structure built from molecules of another substance.

Even though the clathrates of water, the so-called hydrates, are the focus of this work, they are not the only clathrate compounds. For example, urea forms interesting inclusion compounds as well.

Although hydrates were probably encountered by others earlier, credit for their discovery is usually given to the famous English chemist, Sir Humphrey Davy. He reported of the hydrate of chlorine in the early 19th century. In particular, he noted that the ice-like solid formed at temperatures greater than the freezing point of water, and that the solid was composed of more than just water.