It is not so simple as one element per planet. All planets are made of all elements. And their energies and effects are also related to multiple elemental energies.
A good example is Mars has a strong fire energy. But Mars used to be filled with an atmosphere and water just like Earth, and it used to be a very watery planet. Mars is connected to the Sacral chakra which is mostly related to water. You can see this with the Sanskrit Seed mantra VAUM that we use for this chakra that it is a watery energy.