What is an example of a tetrahedral bent molecule other than water?

Apr 27, 2016

$\text{H"_2"S}$ is an easy example. Sulfur is right underneath oxygen in the periodic table, with $Z = 16$.

Since sulfur atom is larger than oxygen atom (it has a new quantum level), the $\text{H"-"S}$ bond length is longer than the $\text{H"-"O}$ bond length. The internuclear distances $\vec{r}$ are:

vecr_("H"-"S") = "133.6 pm"
vecr_("H"-"O") = "95.8 pm"

Thus, the $\text{H"-"S}$ bond is weaker. A weaker bond with a proton (${\text{H}}^{+}$) implies stronger acidity.

Therefore, we can expect $\text{H"_2"S}$ to be a stronger acid than water, and it is. The pKa of water is about $15.7$, whereas the pKa of $\text{H"_2"S}$ is about $7$, which establishes greater acidity for $\text{H"_2"S}$.