In history such as World History? You should be able to distinguish the trends and differences in different periods say "Period 1 vs. Period 2" where each period represents a different range of years (in AP World History I learned it with 6 periods but it varies from year to year of when it is taught)
A polyatomic ion is a group of atoms bond by covalent bonds with an unbalanced charge. A binary ionic compound is composed of atoms of two elements bond by an ionic bond.
