The bond angles in H3 O^+ are less than and greater than ....

The bond angles in $\mathrm{H}_{3} \mathrm{O}^{+}$ are less than _______ and greater than _______. SOLUTION The carbon atom in $\mathrm{CH}_{4}$ has no lone pairs; its bond angles are $109.5^{\circ} .$ The oxygen atom in $\mathrm{H}_{3} \mathrm{O}^{+}$ has one lone pair. A lone pair is more diffuse than a bonding pair, so the $\mathrm{O}-\mathrm{H}$ bonds squeeze together to minimize electron repulsion. However, they do not squeeze as closely together as they do in water $\left(104.5^{\circ}\right),$ where oxygen has two lone pairs. Therefore, the bond angles in $\mathrm{H}_{3} \mathrm{O}^{+}$ are less than $109.5^{\circ}$ and greater than $104.5^{\circ} .$

The bond angles in $\mathrm{H}_{3} \mathrm{O}^{+}$ are less than _______ and greater than _______.
SOLUTION The carbon atom in $\mathrm{CH}_{4}$ has no lone pairs; its bond angles are $109.5^{\circ} .$ The oxygen atom
in $\mathrm{H}_{3} \mathrm{O}^{+}$ has one lone pair. A lone pair is more diffuse than a bonding pair, so the $\mathrm{O}-\mathrm{H}$ bonds squeeze together to minimize electron repulsion. However, they do not squeeze as closely together as they do in water $\left(104.5^{\circ}\right),$ where oxygen has two lone pairs. Therefore, the bond angles in $\mathrm{H}_{3} \mathrm{O}^{+}$ are less than $109.5^{\circ}$ and greater than $104.5^{\circ} .$

Key Concepts

Valence Shell Electron Pair Repulsion (VSEPR) Theory

This theory explains how the geometry of a molecule is determined by the repulsions between electron pairs (both bonding and non-bonding) around a central atom. It predicts the arrangement of these electron pairs to minimize repulsion, which in turn dictates the molecular shape and bond angles.

Lone Pair-Bonding Pair Repulsion

Lone pairs of electrons occupy more space than bonding pairs because they are localized closer to the central atom. This increased repulsion from lone pairs pushes the bonding pairs closer together, reducing bond angles from what would be expected in a molecule with only bonding pairs.

Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms in a molecule. Different numbers of bonding and lone pairs result in various shapes, such as tetrahedral, trigonal pyramidal, and bent, each with characteristic bond angles that deviate from idealized geometries due to electron pair repulsions.

Bond Angle Trends

Bond angles decrease from ideal values when lone pairs are present because the electron repulsion between lone pairs and bonding pairs is greater than that between bonding pairs alone. This trend explains why molecules with one or more lone pairs (like certain oxygen-containing ions) have bond angles that are smaller than those in similar molecules without lone pairs.

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