Which chemical species is not commonly associated with a -2 charge?

Phosphate is a chemical species that is typically associated with a -3 charge, not a -2 charge. This charge occurs because phosphorus, in phosphate, is bonded to four oxygen atoms, and the overall structure of the phosphate ion (PO₄³⁻) reflects the tendency of phosphorus to have a higher oxidation state when bonded with oxygen.

In contrast, thiosulfate, oxalate, and sulfate are species that commonly have a -2 charge. Thiosulfate (S₂O₃²⁻) consists of sulfur and oxygen and carries a -2 charge due to its molecular structure. Oxalate (C₂O₄²⁻) is another example, where carbon and oxygen atoms create a stable ion with a -2 charge. Similarly, sulfate (SO₄²⁻) is composed of sulfur bonded to four oxygen atoms, resulting in a -2 charge in its ionic form.

Recognizing the typical charges of these polyatomic ions is essential for understanding their chemical behavior and reactivity in various contexts within chemistry.