5.5 - Dative Bond

Meaning and Formation

• A dative bond, or coordinate bond, is a covalent bond in which the shared electron pair is contributed by only one atom.
• The donor contributes a lone pair of electrons that was not involved in a covalent bond.

Hydroxonium Ion, ${\mathrm{H}}_3{\mathrm{O}}^{+}$

1. In ${\mathrm{H}}_2\mathrm{O}$, oxygen has a stable octet and each hydrogen has a stable duplet.
2. A hydrogen ion, ${\mathrm{H}}^{+}$, has no electron.
3. Oxygen donates one lone pair to ${\mathrm{H}}^{+}$, forming a dative bond and the hydroxonium ion, ${\mathrm{H}}_3{\mathrm{O}}^{+}$.
4. In ${\mathrm{H}}_3{\mathrm{O}}^{+}$, oxygen retains an octet and every hydrogen has a duplet.

Ammonium Ion, $\mathrm{N}{\mathrm{H}}_4^{+}$

• When hydrogen chloride gas and ammonia gas mix, white fumes of ammonium chloride, $\mathrm{N}{\mathrm{H}}_4\mathrm{Cl}$, form.
• The ammonium ion forms when nitrogen in $\mathrm{N}{\mathrm{H}}_3$ contributes its lone pair to ${\mathrm{H}}^{+}$, producing a dative bond in $\mathrm{N}{\mathrm{H}}_4^{+}$.