Hygroscopic compounds take up water from the air for many different reasons. ... Ionic compounds are often hygroscopic because they form stable hydrates. Metal cations (being positively charged) attract the lone pairs on water oxygens and form coordinate covalent bonds with water.

Why does hygroscopic material absorb water?

9.2. 3 Hygrothermal properties. Straw is a hygroscopic material, which means that it will adsorb water vapor from the air and absorb liquid water when exposed to a suitable source. Adsorption is the process by which water vapor molecules are held on the surface of a material through polar attraction.

Do hygroscopic compounds absorb water?

A hygroscopic substance is able to absorb or adsorb water from its surroundings. Typically, this occurs at or near ordinary room temperature. Most hygroscopic materials are salts, but many other materials display the property.