Ligands are molecules or ions that can bind to a central atom, typically a metal, to form a complex. They have one or more pairs of electrons that they can donate to the metal, which helps stabilize the complex. Ligands can be simple, like water or chloride ions, or more complex, like ethylenediamine. In coordination chemistry, the properties of ligands influence the behavior of the metal complex, including its color, reactivity, and solubility. Ligands are classified based on how many binding sites they have; for example, bidentate ligands can attach at two points, while monodentate ligands attach at one.