Ionic bonding is an important concept you need to know for IGCSE Chemistry:

Ions

Ions are formed when atoms gain or lose electrons to form full outer shell.

Metals: lose electrons and form positively charged ions

Non-metals: gain electrons and form negatively charged ions

For example, a magnesium atom loses the two outer electrons and becomes a magnesium ion.

Similarly, an oxygen atom gains two electrons and becomes an oxide ion.

These are the ionic charges of common ions that you should know 👇

Ionic Compounds and Ionic Bonds

Ionic compounds are formed when a metal transfers electrons to a non-metal.

Ionic bonds from between positively charged ions and negatively charged ions due to electrostatic attraction between opposite charges.

Example 1. Formation of magnesium oxide (MgO)

• Magnesium transfers two outer electrons to oxygen.
• Mg²⁺ ion and O^2- ion are formed.
• The electrostatic attraction between Mg²⁺ ion and O^2- ion forms the ionic bond between magnesium and oxygen.
• The chemical formula for the ionic compound is MgO.

Example 2. Formation of magnesium chloride (MgCl₂)

• Magnesium transfers one electron each to two chlorine atoms.
• One Mg²⁺ ion and two Cl^- ions are formed. 
• The electrostatic attraction between Mg²⁺ ion and Cl^- ion forms the ionic bond between magnesium and chlorine.
• The chemical formula for the ionic compound is MgCl₂.

Ionic Lattices

Ions in an ionic compound are arranged in a regularly repeating pattern called the ionic lattice.

Ionic lattices are formed because there is a strong electrostatic force acting between ions.

👆 This is an example of a 3D ionic lattice formed by sodium chloride (NaCl).

Properties of Ionic Compounds

I. High Melting and Boiling Points

• For a substance to melt or boil, energy is needed to break the bonds between particles.
• Ionic compounds are held together by many strong electrostatic forces, therefore need a large amount of energy to break the ionic bonds.
• Ionic compounds have high melting and boiling points, and they are usually solid in room temperature.

II. Electricity Conduction

• If ionic compounds are molten or in aqueous state, electrically charged particles are free to move around. Therefore, they can conduct electricity.
• In solid state, ions are fixed in the lattice, so electricity cannot be conducted.

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