Formula Unit, Ion , Molecular ion and Free Radical

Formula Unit, Ion, Molecular ion and Free Radical

Write a note on the following

1. Formula Unit 

2. Ion

3. Molecular ion

4. Free Radical

FORMULA UNIT

The smallest repeating unit of an ionic compound which shows the simplest ratio between its ions is called the formula unit.

EXAMPLE

The simplest ratio between Mg and Cl in the crystal lattice of MgCl is 1:1 hence the formula unit of magnesium chloride is MgCl

ION

When an atom loses or gains an electron it becomes a charged particle known as an ion.

EXPLANATION

An atom most of the time is electrically neutral but when it gains or loses an electron an additional charge appears on it the newly charged specie is known as an ion.

Types of Ions

There are two types of ions

  • Cation
  • Anion

CATION

The charged specie that is formed by the loss of electrons is known as a cation.

The number of protons are greater than electrons in a cation

EXAMPLE

Mg+2 ,H+1

ANION

 The charged specie that is formed by the gain of electrons is known as an anion.

the number of electrons are greater than protons in anions.e.g Cl-1,O-2

Molecular ion

When a molecule loses or gains an electron it becomes a new chemical specie known as a molecular ion.

Explanation

Molecular ions that contain a positive charge are formed by the loss of an electron from neutral molecules.

Molecular ions having a negative charge are formed by the gain of an electron from neutral molecules.

Examples

Positive molecular ions are known as molecular cations

e.g

O2+ ,CH4+ , H3O+ , NH4+

Negative molecular ions are known as molecular anions

e.g

SO4-2, OH

Free radical

An atom or molecule having an unpaired electron in its valence shell is termed a free radical.

EXPLANATION

A free radical is formed by the homolytic fission of a molecule such that each atom in the molecule obtains an unpaired electron. A free radical has no charge and is represented by a  [.] on the symbol of the element. It is a highly reactive specie and cannot exist independently.

Reaction involving free radicals

Cl2 → 2Cl.

The chlorine-free radical will react with methane CH4 to form methyl free radical.

CH4 + Cl.→ CH3. + HCl

Now the methyl free radical reacts with another Cl2 molecule to form chloromethane and chlorine free radical

CH3. + Cl2→CH3Cl + Cl.

The reaction goes on until the formation of a stable product.

Classify the following as Cation, Anion, Molecular ion, Free Radical and Molecules

Classify the following as Cation , Anion, Molecular ion, Free Radical and Molecules

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