Ionic Bond

Definition

An ionic bond (electrovalent bond) is the electrostatic force of attraction between oppositely charged ions formed by the complete transfer of one or more electrons from one atom to another.

This concept was first explained by Walther Kossel and Gilbert N. Lewis in 1916.

Usually:

• Metals lose electrons → cations
• Non-metals gain electrons → anions

The attraction between these ions forms the ionic bond.

Formation of Ionic Bond (Example: NaCl)

Step 1: Electronic Configuration

Sodium (Na)
Atomic number = 11
Electronic configuration =1s² 2s² 2p⁶ 3s¹

Chlorine (Cl)
Atomic number = 17
Electronic configuration =1s² 2s² 2p⁶ 3s² 3p⁵

Sodium has one valence electron, while chlorine needs one electron to complete its octet.

Step 2: Electron Transfer

Sodium loses one electron:

Na → Na⁺ + e^–

Chlorine gains one electron:

Cl + e^– → Cl^–

Step 3: Formation of Ions

Na → Na⁺ (cation)
Cl → Cl^– (anion)

Step 4: Electrostatic Attraction

The Na⁺ ion and Cl^– ion attract each other due to opposite charges.

Na⁺ + Cl^– → NaCl

This attraction forms the ionic bond.

Ionic Bond Structure (Crystal Lattice)

In ionic compounds, ions do not form single molecules.
Instead they form a three-dimensional crystal lattice.

Characteristics of lattice structure:

• Each Na⁺ ion is surrounded by 6 Cl^– ions
• Each Cl^– ion is surrounded by 6 Na⁺ ions
• This arrangement increases stability and lattice energy

Example: Sodium chloride crystal structure

Energy Changes in Ionic Bond Formation

1. Ionization energy
   Energy required to remove an electron from a metal atom.
2. Electron affinity
   Energy released when a non-metal gains an electron.
3. Lattice energy
   Energy released when gaseous ions form an ionic crystal.

High lattice energy makes ionic compounds very stable.

Characteristics of Ionic Bonds

1. Strong electrostatic force of attraction
2. High melting and boiling points
3. Hard crystalline solids
4. Conduct electricity in molten or aqueous state
5. Soluble in polar solvents like water
6. Insoluble in non-polar solvents

Examples of Ionic Compounds