The word chelate comes from the Greek word chele, meaning crab's claw. A chelate is a chemical compound in which one atom is enclosed within a larger cluster of atoms that surround it like an envelope. A chelate is formed from a chelating agent plus a metal ion. The chelating agent wraps around a metal ion and attaches in several places. Compounds that attach to metal ions by sharing their electrons are known as ligands. Ligands that can attach in two places are called bidentate (two-bite) ligands. Those that attach in three places are tridentate, or three-bite ligands. There are even hexadentate ligands such as ethylene diammine tetraacetic acid, commonly known as EDTA. Chelating agents are bidentate or higher ligands. When you picture a ligand "biting" the metal ion from two sides, you can picture the pincers of a crab. Chelate compounds are very stable.

Chelates occur naturally...