1) Alternate 2) Alternating 
• (v. t.) Composed of alternate layers, as some rocks.
A conjugated system of pi electrons is termed alternant if its atoms can be divided into two sets so that no atom of one set is directly linked to any other atom of the same set. 
Al·ter'nant adjective [ Latin alternans , present participle: confer French alternant . See Alternate , transitive verb ] (Geol.) Composed of alternate layers, as some rocks. 
alternating; alternate.