Polymers with carbonyl groups can form multivalent anions. Each antibody has at least two antigen-binding sites, therefore antibodies are bivalent to multivalent. Since particles are frequently negatively charged, multivalent metal cations thus represent highly effective coagulants. Many flocculants are multivalent cations such as aluminium, iron, calcium or magnesium. This clustering allows for binding of multivalent, branched ligands such as high-mannose N-linked oligosaccharides. Hardness of water is determined by the concentration of multivalent cations. Vaccines may be "monovalent" (also called "univalent") or "multivalent" (also called "polyvalent"). Generally multivalent ions contribute strongly to the ionic strength. Water's hardness is determined by the concentration of multivalent cations in the water. The multivalent vanadium cation (V<->V) plays an important role to accomplish the multi-electron reactions. It is potentially multivalent for attachment to the complement fixation sites of immunoglobulin. More commonly, the dispersion is destabilized (sometimes called "broken") by addition of a multivalent cation. "Sulfur" (symbol S) is an abundant multivalent nonmetal, one of chalcogens. It is abundant, multivalent, and nonmetallic. In contrast, topological spaces are generally non-isomorphic; their theory is "multivalent".