Question

Explain the formation of $H_3{O}^{+}$ and ${\mathrm{NH}}_4^{+}$ ion

Answer 1

Formation of Hydronium ion:
This ion is formed by the combination of water molecule and $H^{+}$ ion. The water molecule has two O—H covalent bonds and central oxygen atom has two lone pairs of electrons. $H^{+}$ ion is shoet of 2 to achieve electron configuration of helium. During the formation of $H_3{O}^{+}$, one pair of lone pair from O-atom is donated to the vacant shell of $H^{+}$ ion and O → $H^{+}$ coordinate bond is formed. Thus $H_3{O}^{+}$ ion contains two O—H covalent bonds and one O → $H^{+}$ coordinate bond.

Formation of Ammonium ion :
This ion is formed by the combination of ${\mathrm{NH}}_3$ molecule and $H^{+}$ ion. In ${\mathrm{NH}}_3$ molecule each of three H-atoms is linked to N-atom by a covalent bond. Thus in this molecule N-atom is left with a lone pair of electrons after completing its octet by sharing three of its valence shell electrons with three H-atoms. The electrons of lone pair on N-atom are donated to $H^{+}$ ion and thus a N—H coordinate bond is established in ${\mathrm{NH}}_4^{+}$ ion.