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
*********************************
*********************************
Related Chemistry pdf‘s
10th Class Chemistry pdf Notes
11th Class Chemistry Chapterwise Free pdf Notes
12th Class Chemistry Free Downloadable
