Chemical substances are broadly classified into distinct categories based on molecular composition, bonding, and functional properties: (1) organic chemicals, composed primarily of carbon and hydrogen chains; (2) inorganic chemicals, encompassing minerals, metals, salts, and non-carbon compounds; (3) polymers and plastics, consisting of massive macromolecular chains; (4) specialty and fine chemicals, engineered for high-purity or niche uses; and (5) biochemicals, which include natural organic compounds, proteins, and enzymes essential for life.