A polyatomic element is a chemical element that naturally exists as a compound molecule containing more than two atoms of the same element joined together by covalent bonds. There are only three polyatomic elements found on the periodic table: selenium, phosphorous and sulfur.
When pure selenium is found in nature, it exists as a ring of eight selenium atoms. Similarly, sulfur also exists in this same structure at room temperature. The two types of phosphorous, white and red, both consist of four phosphorous atoms linked together. The difference between the two is how the molecules are bonded together and formed.