Question

Why is $H_2O$ monodentate and has 2 lone pairs?

• A. The oxygen atom in $H_2O$ has 6 valence electrons. It forms two single covalent bonds with two hydrogen atoms, using 2 of its electrons. The remaining 4 electrons form two lone pairs on the oxygen atom. Water binds to a metal center through one of these lone pairs on the oxygen atom, making it a monodentate ligand.
• B. The oxygen atom in $H_2O$ has 8 valence electrons. It forms two double covalent bonds with two hydrogen atoms, using 4 of its electrons. The remaining 2 electrons form one lone pair on the oxygen atom. Water binds to a metal center through both lone pairs on the oxygen atom, making it a bidentate ligand.
• C. The oxygen atom in $H_2O$ has 6 valence electrons. It forms two single covalent bonds with two hydrogen atoms, using 2 of its electrons. The remaining 4 electrons form two lone pairs on the oxygen atom. Water binds to a metal center through the hydrogen atoms, making it a monodentate ligand.
• D. The oxygen atom in $H_2O$ has 8 valence electrons. It forms one double covalent bond with two hydrogen atoms, using 2 of its electrons. The remaining 6 electrons form three lone pairs on the oxygen atom. Water binds to a metal center through one of these lone pairs on the oxygen atom, making it a monodentate ligand.

Answer 1

Answer: (A)

The oxygen atom in $H_2O$ has 6 valence electrons. It forms two single covalent bonds with two hydrogen atoms, using 2 of its electrons. The remaining 4 electrons form two lone pairs on the oxygen atom. Water binds to a metal center through one of these lone pairs on the oxygen atom, making it a monodentate ligand.

Answer 2

Oxygen, in Group 16, has 6 valence electrons. In $H_2O$, oxygen forms two single covalent bonds with two hydrogen atoms, utilizing 2 valence electrons. This leaves $6 - 2 = 4$ valence electrons on oxygen, which form two lone pairs. In coordination chemistry, a ligand's denticity refers to the number of donor atoms it uses to bind to a metal. Water acts as a ligand by donating a lone pair from its oxygen atom to form a coordinate covalent bond. Since it binds through only one atom (oxygen), it is classified as a monodentate ligand.