Predict the shape of a methanal, H_{2}CO, molecule, better known by its common name, formaldehyde.
The Lewis formula for a H_{2}CO molecule is
\begin{matrix} H_{_{\diagdown }} \\ \hspace{45 pt} C=O^{^{.}.}_{_{.}.} \\ H^{^{\diagup }}\end{matrix}We treat the double bond as one group of electrons and classify H_{2}CO as an AX_{3} molecule. We predict (correctly) that H_{2}CO is a trigonal planar molecule; in other words, all four atoms lie in a single plane. Figure 8.14 shows a space-filling model of a formaldehyde molecule.