Molecular polarity depends on two factors: the type of bonds in a molecule and the arrangement of those bonds. For diatomic molecules, bond polarity and molecular polarity are the same. However, for larger molecules the arrangement of bonds must be considered. A molecule may contain polar bonds but not be polar itself if it is symmetric, as the "pull" from one polar bond cancels out the "pull" from another. Symmetry can be determined by the presence of at least one mirror plane. Nonpolar molecules like CO2 are symmetric with polar bonds that cancel out, while polar molecules like H2O are asymmetric with polar bonds that do not cancel out.