Polyatomic ions and ionic compounds.

Polyatomic ions and ionic compounds.

• A. Polyatomic ions are always excluded from ionic bonding.
• B. Polyatomic ions are examples of ionic species that can be part of ionic compounds.
• C. Polyatomic ions form covalent bonds with metals.
• D. Polyatomic ions only occur in molecular compounds.

Answer: (B)

Polyanionic or polyatomic ions are charged groups of atoms that act as a single unit in ionic compounds. Because they carry a net charge, they can engage in electrostatic attractions with counterions to form salts. Inside the ion, the atoms are held together by covalent bonds, but the interaction between the polyatomic ion and a metal or other counterion is ionic. This is why you see polyatomic ions like ammonium (NH4+) or sulfate (SO4^2− in salts such as ammonium chloride or calcium sulfate). The idea that polyatomic ions are excluded from ionic bonding is not correct, since they are common partners in ionic compounds. The notion that they form covalent bonds with metals misunderstands the bonding in the lattice—the metal–polyatomic ion bond is ionic. And they do not occur only in molecular compounds; they are key components of many ionic salts.

Polyanionic or polyatomic ions are charged groups of atoms that act as a single unit in ionic compounds. Because they carry a net charge, they can engage in electrostatic attractions with counterions to form salts. Inside the ion, the atoms are held together by covalent bonds, but the interaction between the polyatomic ion and a metal or other counterion is ionic. This is why you see polyatomic ions like ammonium (NH4+) or sulfate (SO4^2− in salts such as ammonium chloride or calcium sulfate). The idea that polyatomic ions are excluded from ionic bonding is not correct, since they are common partners in ionic compounds. The notion that they form covalent bonds with metals misunderstands the bonding in the lattice—the metal–polyatomic ion bond is ionic. And they do not occur only in molecular compounds; they are key components of many ionic salts.