What Is Ionic Bonding?

Ionic bonding is a type of chemical bonding that occurs when electrons are transferred from one atom to another, forming charged particles called ions.

This type of bonding usually occurs between a metal and a non-metal.

When electrons are transferred:

• The atom that loses electrons becomes a positive ion (cation)
• The atom that gains electrons becomes a negative ion (anion)

The opposite charges attract each other, forming a strong electrostatic force called an ionic bond.

What Are Ions?

Ions are atoms or groups of atoms that carry a positive or negative charge because they have lost or gained electrons.

Two types of ions exist:

Positive Ions (Cations)

Positive ions form when atoms lose electrons.

Example:

Sodium atom:

Na → loses 1 electron → Na⁺

Negative Ions (Anions)

Negative ions form when atoms gain electrons.

Example:

Chlorine atom:

Cl → gains 1 electron → Cl⁻

Formation of Ionic Bonds

Ionic bonds form when one atom transfers electrons to another atom.

Example: Sodium Chloride (NaCl)

Step 1
Sodium has electronic configuration:

2,8,1

It loses one electron to become stable:

Na → Na⁺ (2,8)

Step 2
Chlorine has electronic configuration:

2,8,7

It gains one electron:

Cl → Cl⁻ (2,8,8)

Step 3
The positive sodium ion and negative chloride ion attract each other, forming an ionic bond.

This produces the compound sodium chloride (NaCl).

Ionic Lattice Structure

Ionic compounds form a giant ionic lattice structure.

This structure is a regular arrangement of alternating positive and negative ions.

The strong attraction between oppositely charged ions holds the structure together.

This explains many properties of ionic compounds.

Properties of Ionic Compounds

Ionic compounds have several characteristic properties.

High Melting and Boiling Points

Ionic compounds have high melting and boiling points because strong forces of attraction exist between ions.

A large amount of energy is needed to break these bonds.

Electrical Conductivity

Ionic compounds can conduct electricity when molten or dissolved in water.

This happens because the ions become free to move and carry electrical charge.

However, ionic compounds do not conduct electricity when solid, because the ions are fixed in place.

Crystal Structure

Many ionic compounds form crystalline solids with regular geometric shapes.

Example:

Sodium chloride forms cube-shaped crystals.

Examples of Ionic Compounds

Common examples of ionic compounds include:

• Sodium chloride (NaCl)
• Magnesium oxide (MgO)
• Calcium chloride (CaCl₂)
• Potassium bromide (KBr)

These compounds form when metals react with non-metals.

Why Ionic Bonding Is Important

Understanding ionic bonding helps students explain:

• Formation of chemical compounds
• Structure of solids
• Electrical conductivity of substances
• Chemical reactions involving ions

It is one of the most important bonding concepts in O Level Chemistry.

Exam Tip (5070)

Students are often asked to:

• Define ionic bonding
• Explain how ions form
• Describe the structure of ionic compounds

Example exam question:

Define an ionic bond.

Answer:

An ionic bond is the strong electrostatic attraction between oppositely charged ions.

Practice Question

Magnesium has electronic configuration:

2,8,2

Chlorine has electronic configuration:

2,8,7

Explain how magnesium chloride forms.

Answer

Magnesium loses two electrons to form Mg²⁺.

Each chlorine atom gains one electron to form Cl⁻.

Two chloride ions combine with one magnesium ion to form MgCl₂.

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