Monodentate ligands are Lewis bases that donate a single pair ("mono") of electrons to a metal atom. Monodentate ligands can be either ions (usually anions) or neutral molecules.

Some Monodentate Ligands
ligand	Lewis structure	name	ligand	Lewis structure	name
F-		fluoride ion	Cl-		chloride ion
Br-		bromide ion	I-		iodide ion
H2O		water	NH3		ammonia
OH-		hydroxide ion	CO		carbon monoxide
CN-		cyanide ion	SCN-		thiocyanate ion

Chemists often represent ligands as spheres for simplicity, even though the "sphere" sometimes has three-dimensional structure of its own. For example, when chemists draw the structure for [Ni(NH₃)₆]²⁺, each ammonia ligand is represented as a sphere. The sphere represents the donor atom of the ligand. In [Ni(NH₃)₆]²⁺, the donor atoms are the nitrogen atoms of the NH₃ ligands (NOT the hydrogen atoms).

		= Ni = N = H
[Ni(NH3)6]2+ abbreviated structure Note: only the donor atoms (N atoms) of the NH3 ligands are shown.	[Ni(NH3)6]2+ complete structure Note: all atoms are shown.

Applications

		= Cu/Rh = N = H = O = C = I
[Cu(NH3)4]2+ Used in some brands of waterbed conditioners to inhibit the growth of fungi and bacteria. Note the square planar structure.	[RhI2(CO)2]- Used as a catalyst in the Monsanto Process for making acetic acid. Note the square planar structure.