Bonding and Structure

A lattice is a regular, repeating three-dimensional arrangement of particles (atoms, ions, or molecules) in a solid. Think of it like a perfectly organized stack of building blocks where every block sits in exactly the right position. Most crystalline solids (solids with an ordered structure) are made up of these lattice arrangements.

There are four main types of lattice structures you need to know:

• Giant ionic
• Simple molecular
• Giant molecular (also called giant covalent)
• Giant metallic

Giant ionic lattices are made up of millions of positively charged metal ions (cations) and negatively charged non-metal ions (anions) arranged in a regular, repeating pattern. The particles are held together by strong electrostatic forces of attraction between opposite charges. This type of force is called ionic bonding.

The word "giant" means the structure extends throughout the whole crystal in all directions—there are no individual molecules, just a continuous network of ions.

In sodium chloride (common table salt):

• Each Na⁺ ion is surrounded by 6 Cl⁻ ions
• Each Cl⁻ ion is surrounded by 6 Na⁺ ions
• The ions alternate in a cubic (box-like) arrangement
• The negative ions (Cl⁻) are bigger than the positive ions (Na⁺)

Magnesium oxide has a similar cubic structure to sodium chloride:

• Each Mg²⁺ ion is surrounded by 6 O²⁻ ions
• Each O²⁻ ion is surrounded by 6 Mg²⁺ ions
• The ratio of cations to anions is 1:1 (one positive ion for each negative ion)

The type of lattice formed depends on the sizes of the ions and the ratio between them.

Ionic compounds are hard but brittle (they shatter when hit). When you apply a force to an ionic crystal, the layers of ions can shift slightly. When this happens, ions with the same charge end up next to each other. Because like charges repel, the crystal breaks apart.