What is an Ion?
Ions are charged species that are formed when an atom loses or gains electrons. The word ion is derived from the Greek word ἰόν which means ‘going’. If an atom transfer electrons from its outermost orbit it tends to form an ion. Ions are formed in both cases when an atom loses an electron or when an atom gains an electron. Ions are formed by the atoms to attain the nearest noble gas configuration. As we know atoms are electrically neutral species, so
If an atom loses an electron the total positive charge exceeds the total negative charge and an overall positive charge is gained by the atom the atom, in this case, is called a cation. Some examples of cations are Na+, Ca+, Fe2+, etc.
Similarly, if an atom gains an electron the total negative charge exceeds the total positive charge, and an overall negative charge is gained by the atom, and the atom in this is called an anion. Some examples of anions are O2-, OH–, Cl–, etc.
The image below shows the formation of cations and anions.
On the basis of the number of elements in an ion, ions are classified into two categories,
- Monoatomic Ions: Ions formed by only one atom are classified as monoatomic ions they can be either positive or negative. Example, Na+, Cl–, etc.
- Polyatomic Ions: Ions formed by a group of atoms are classified as polyatomic ions they can be either positive or negative. Example, (NH4)+, CN–, etc.
Cations vs Anions
Ions are charged species that are formed by the transfer of electrons from the outermost shell. Ions are either positive or negative in nature depending on the overall charge of the ion. If an atom loses an electron it has excess proton forming positive ions whereas if an atom gains an electron it has excess electrons forming negative ions.
In an aqueous solution of sodium chloride (NaCl), Na exists as a positive ion (cation) Na+, while Cl exists as a negative ion (anion) Cl–. Because both of them have opposite charges they are attracted to one another creating an ionic bond.
Let’s learn more about ions, their types (cations and anions), and the difference between cations and anions in this article.
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