Question

Summarize the main differences between type A, type B and borderline metals. Explain why the presence of organic matter in natural waters and in sediments is important for the fate of metals in the environment.

Answer 1

Metals are classified based on the stability of complex formed with more and less electronegative ligands

Type A metal include group 1 and group 2 metals and lighter transition metal in high oxidation state (e.g Co3+, Ti4+,Fe3+)

Type A metal are classified as hard metal and it will have low polarizability, these metal will prefer to form stable complex high electronegative atom like oxygen, fluorine containing ligands compare to sulfur and higher halides containing ligands, these type of metal prefer to form ionic bonds with ligands.

Type B metal include heavier transtition metal ions like Cu+, Ag+, Au+, Tl+, Ga+, Zn2+ arc.

Type B metal are classified as soft metal, they exhibit high polarizabiliry, Type B metal will prefer to form complex with liganf containing less electronegative atom like sulfur, iodine, bromine, chlorine nitrogen. Metal type will have covalent bonding with ligand.

Borderline metal include V2+, Cr2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+ etc.

Borderline metals will form complex with all types ligands, in border line metals type B character increases as we move from left to right in the periodic table.

Organic mater in natural water and in sediments is important for binding, mobility and transportation of metal