1.3 Chemical Species

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Chemical Species

Ion

An ion is an atom or group of atoms having a charge on it. The charge may be positive or negative.

Cations

An atom or group of atoms having a positive charge on it is called a cation. The cations are formed when atoms lose electrons from their outermost shells. For example, Na +, K + are cations.

The following equations show the formation of cations from atoms.

H → H + + 1e -

Na → Na + + 1e -

Ca → Ca 2+ + 2e -

Anions

An atom or a group of atoms that has a negative charge on it is called an anion. Anion formed by the gain or addition of electrons to an atom. For example, Cl - and O 2-.

The following examples show the formation of an anion by the addition of electrons to an atom.

Cl + 1e - → Cl -

O + 2e - → O 2-

Molecular Ion

When a molecule loses or gains an electron, it forms a molecular ion. Hence, molecular ion or radical is a species having a positive or negative charge on it. Like other ions, they can be cationic molecular ions (if they carry a positive charge) or anionic molecular ions (if they carry a negative charge). Cationic molecular ions are more abundant than anionic molecular ions. For example, CH4 +, He +, N2 +. When gases are bombarded with high-energy electrons in a discharge tube, they ionize to give molecular ions.

Free Radicals

Free radicals are atoms or groups of atoms possessing an odd number of (unpaired) electrons. It is represented by putting a dot over the symbol of an element e.g. H•, Cl•, H3C•. Free radicals are generated by the homolytic (equal) breakage of the bond between 3 two atoms when they absorb heat or light energy. A free radical is an extremely reactive species as it has the tendency to complete its octet.

Cl2 → 2Cl•

CH4 → H3C• + H•

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Hello, this is Misbah ud Din a student of STEM. This is my blog chemisTREEpk which provides a vast knowledge about Chemistry(and sometimes other sciences) fully free.

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