# Concept of an Ion

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Compounds composed of metals and nonmetals contain charged species. The charged species are known as ions. An ion is a charged particle and can be negatively or positively charged. A negatively charged ion is called an ‘anion’ and the positively charged ion, a ‘cation’. Take, for example, sodium chloride (NaCl). Its constituent particles are positively charged sodium ions (Na+) and negatively charged chloride ions (Cl– ). Ions may consist of a single charged atom or a group of atoms that have a net charge on them. A group of atoms carrying a charge is known as a polyatomic ion.

(i) Cation: It is positively charged ion and is formed by the loss of electron from an atom e.g. H+, Na+, Ca2+, Al3+, NH4+ etc.
(ii) Anion: It is negatively charged ion and is formed by the gain of electrons by an atom, e.g. Cl–, O2-, C–, F–, CO32- PO43- etc.

Some ionic compounds :

 Ionic Compound Constituting Elements Ratio by Mass Calcium oxide Calcium and oxygen 5:2 Magnesium sulphide Magnesium and sulphur 3:4 Sodium chloride Sodium and chlorine 23:35.5

# Concept of an Ion:

The charged species are known as ions. A negatively charged ion is called an 'anion' and the positively charged ion, a 'cation'.

A group of atoms carrying a charge is known as a polyatomic ion.

 Anions Cl-, Br-, O2-, N3- Cations Na+, K+, Cu+, Al3+ Polyatomic ions """NH"_4^+, "OH"^–, """HCO"_3^-, "PO"_4^3–
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