# What is a planar molecule?

For instance, we conventionally say that ${\text{H"_2"C"="CCl}}_{2}$ (1,1-dichloroethylene) lays on the $y z$-plane, and that its $2 {p}_{x}$ atomic orbitals form the $\text{C"-"C}$ $\pi$ bond, since the principal (${C}_{2}$) rotation axis is along the $\text{C"="C}$ bond, defined as the $z$ axis: