Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature.

What causes hygroscopicity?

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.

What is hygroscopicity in chemistry?

Hygroscopicity is the tendency of a solid substance to absorb moisture from the surrounding atmosphere. The process can take on a number of forms. Thus, with a porous solid such as activated carbon, water vapor will be physically adsorbed, both on the external surface and within the pores, to form a condensed layer.