The hydronium ion (H_3O^+) is formed when a hydrogen ion bonds to a water molecule. Based … — JAMB UTME

The hydronium ion ( $H_3O^+$ ) is formed when a hydrogen ion bonds to a water molecule. Based on Valence Shell Electron Pair Repulsion (VSEPR) theory, what is the molecular geometry and the hybridization state of the central oxygen atom in $H_3O^+$ ?

Trigonal pyramidal geometry with $sp^3$ hybridizationAnswer
B
Tetrahedral geometry with $sp^3$ hybridization
C
Trigonal planar geometry with $sp^2$ hybridization
D
Bent geometry with $sp^2$ hybridization

Answer

The central oxygen atom in

H_3O^+

sp^3

hybridized, and the ion exhibits a trigonal pyramidal molecular geometry.

H_3O^+

, the central oxygen atom forms three single covalent bonds with hydrogen atoms and retains one lone pair. The total of four electron pairs creates a tetrahedral electron arrangement, which corresponds to

sp^3

hybridization. Because one of the four domains is a non-bonding lone pair, the positions of the atomic nuclei define a trigonal pyramidal molecular geometry.

Step-by-Step Solution

Calculate valence electron pairs around the central oxygen atom in

H_3O^+

Oxygen supplies 6 valence electrons, three hydrogens supply 3, and subtracting 1 for the positive charge leaves 8 valence electrons (4 electron pairs).

Determining steric number requires counting both bonding and non-bonding electron pairs.

Determine the electron-pair geometry and hybridization

Four electron pairs arrange tetrahedrally around oxygen, requiring

sp^3

hybridization.

Four steric domains around a central atom always correspond to an

sp^3

set of hybrid orbitals.

Deduce the molecular shape

With 3 bonding pairs and 1 non-bonding lone pair, the molecular shape is trigonal pyramidal.

Molecular geometry reflects only the arrangement of the atomic nuclei around the central atom.

Key Concept

VSEPR Theory and Hybridization of Polyatomic Ions

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