What are polyatomic ions? Give examples.

Answer

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Hint:Not every ions have a single atom like

N a^{+}

S^{+}

but some ions are combinations of atoms (polyatomic) such as sulfate ion

- S O_{4}^{2 -}

. It is the polyatomic ion; one sulfur is bound to four oxygen with covalent bonds.

Complete step by step answer:A polyatomic ion is also known as a molecular ion and it is a charged chemical species (ion) composed of two or more atoms covalently bonded. It can also be known as a metal complex that acts as a single unit. Example -

S O_{4}^{2 -}, C O_{3}^{2 -}

. These are the ions which consist of more than one atom just like nitrate ions, containing one nitrogen atom and three oxygen atoms. The nitrate ion has one more electron than protons in total. These ions act as a single unit of charge when balancing charges in an ionic compound. A polyatomic ion is defined as poly means many, atomic means atom, and ion means atom with a charge.
Common polyatomic ions:
Phosphate -

P O_{4}^{3 -}

contains 3- ions.
Ammonium -

N H_{4}^{+}

contains +1 ion.
Carbonate -

C O_{3}^{2 -}

contains 2- ions.
Hydroxide -

O H^{-}

contains 1- ion.
Cyanide -

C N^{-}

contains 1- ion.

Additional information:
In a polyatomic ion when another ion joins it in a compound and the same rules apply as with other ions to determine the simplest ratio to balance the charges.
For example: The formula of ionic compounds made with the calcium ion and the phosphate ion. To identify ions: Calcium ion =

C a^{2 +}

and Phosphate ion =

P O_{4}^{3 -}

.
To balance charges: 3 calciums (6+ total) required balancing 2 phosphate (6- total) i.e.

C a_{3} {(P O_{4})}_{2}

.

Note: Polyatomic ions have some specialty that it has more than two covalently bonded atoms resembling single ions and forming ionic bonds with ions and act as a unit. Remember that ions which end with –ide are monatomic ions whereas ions end with –ate are polyatomic ions.