Predict the shape and the H–O–H bond angles for a hydronium ion, [latex]H_{3}O^{+}[/latex].

The Lewis formula for a [latex]H_{3}O^{+}[/latex] ion is [latex]\begin{bmatrix} H -\overset{..}{O}- H \\\overset{|}{H} \end{bmatrix} ^{\oplus }[/latex] There are three hydrogen ligands and one lone pair attached to the central oxygen atom. Thus, it belongs to the class [latex]AX_{3}E[/latex] . We see from Table 8.2 that it has a trigonal pyramidal shape. The H–O–H bond angles for a [latex]H_{3}O^{+}[/latex] ion will be somewhat less than that of an ideal tetrahedron and so we predict that the angle is <109.5°.

Question 8.4: Predict the shape and the H–O–H bond angles for a hydronium ......

General Chemistry [1096620]

Predict the shape and the H–O–H bond angles for a hydronium ion, $H_{3}O^{+}$ .

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The Lewis formula for a $H_{3}O^{+}$ ion is

\begin{bmatrix} H -\overset{..}{O}- H \\\overset{|}{H} \end{bmatrix} ^{\oplus }

There are three hydrogen ligands and one lone pair attached to the central oxygen atom. Thus, it belongs to the class $AX_{3}E$ . We see from Table 8.2 that it has a trigonal pyramidal shape. The H–O–H bond angles for a $H_{3}O^{+}$ ion will be somewhat less than that of an ideal tetrahedron and so we predict that the angle is <109.5°.

TABLE 8.2 Molecular shapes. the white spheres represent the central atom, the red spheres represent ligands, and the green lobes represent lone pairs.
Molecular class	Ideal shape	Examples	Molecular class	Ideal shape	Examples
$AX_{2}$		$CO_{2},\ HCN,\ BeCl_{2}$	$AX_{4}E$		$SF_{4},\ XeO_{2}F_{2},\ IF^{+}_{4}, IO_{2}F^{–}_{2}$
$AX_{3}$		$SO_{3},\ BF_{3},\ NO_{3}^{–},\ CO_{3}^{2–}$	$AX_{3}E_{2}$		$CIF_{3},\ BrF_{3}$
$AX_{2}E$		$SO_{2},\ O_{3},\ PbX_{2},\ SnX_{2}$ (where X is a halogen)	$AX_{2}E_{3}$		$XeF_{2},\ I^{–}_{3},\ IF^{–}_{2}$
$AX_{4}$		$SiH_{4},\ CH_{4},\ SO_{4}^{2–},\ ClO_{4}^{–},\ PO^{3-}_{4},\ XeO_{4}$	$AX_{6}$		$SF_{6},\ IOF_{5}$
$AX_{3}E$		$NH_{3},\ PF_{3},\ AsCl_{3}, ClO^{–}_{3},\ H_{3}O^{+},\ XeO_{3}$	$AX_{5}E$		$IF_{5},\ TeF_{5}^{–},\ XeOF_{4}$
$AX_{2}E_{2}$		$H_{2}O,\ OF_{2},\ SF_{2}$	$AX_{4}E_{2}$		$XeF_{4}, ICI_{4}^{-}$
$AX_{5}$		$PCl_{5},\ AsF_{5},\ SOF_{4}$