5th Period is similar to the 4th Period and consists of 18 Elements Rubidium (Rb) to Xenon (Xe) (atomic nos. 37 to 54).
6th Period contains 32 elements Cesium (Cr) to Radon (Rn), (atomic nos. 55 to 86). THis Period is the longest. The first three elements resemble the corresponding first three elements of the 5th Period. The fourteen earth elements are very much alike in their properties.