Silica gel is an amorphous and porous form of silicon dioxide (silica), consisting of an irregular tridimensional framework of alternating silicon and oxygen atoms with nanometer-scale voids and pores. The voids may contain water or some other liquids, or may be filled by gas or vacuum. 

Characteristic

Silica gel's high specific surface area (around 750–800 m2/g (230,000–240,000 sq ft/oz))allows it to adsorb water readily, making it useful as a desiccant (drying agent). Silica gel is often described as "absorbing" moisture, which may be appropriate when the gel's microscopic structure is ignored, as in silica gel packs or other products. However, material silica gel removes moisture by adsorption onto the surface of its numerous pores rather than by absorption into the bulk of the gel.

Polarity of silica gel

Silica gel is primarily composed of silicon dioxide (SiO2), a compound consisting of silicon and oxygen atoms. The structure of SiO2 is a three-dimensional lattice held together by covalent bonds. The covalent bonds between silicon and oxygen are considered polar because oxygen is more electronegative than silicon, which attracts electrons more strongly, creating partial positive and negative charges within the molecule. Simply put, polarity refers to the presence of positive and negative charges in a molecule. In the case of silica gel, its surface is polar because of the presence of polar groups.