Classification of Structures

The Basics

A chemical structure comprises atoms and the bonds between them.
Chemical structures can be divided into three types: simple molecular structures, giant covalent structures, and giant ionic structures.
The structure type influences properties such as boiling point, melting point, and solubility.

Simple Molecular Structures

Simple molecular structures consist of distinct molecules held together by intermolecular forces.
A molecule is a group of two or more atoms held together by covalent bonds.
These structures might consist of single atoms, as in noble gases, or multiple atoms, as in water and carbon dioxide.
The properties of these structures, including their low melting and boiling points, can be attributed to the weak intermolecular forces.
Intermolecular forces can be easily broken, enabling these substances to change from solid to liquid or gas at relatively low temperatures.

Giant Covalent Structures

Giant covalent structures contain a massive number of atoms linked together by covalent bonds forming a continuous network.
Common examples include diamond, graphite, and silicon dioxide.
These structures have high melting and boiling points due to the considerable amount of energy required to break the many strong covalent bonds.
They typically do not conduct electricity, with the exception of graphite and certain forms of silicon.

Giant Ionic Structures

Giant ionic structures form when metal atoms lose electrons to form positive ions, and non-metal atoms gain these electrons to form negative ions.
The differing charges of the positive and negative ions bind them together in a lattice structure. Common examples are sodium chloride and magnesium oxide.
These structures have high melting and boiling points as well due to the strong electrostatic forces of attraction, known as ionic bonds, between the oppositely charged ions.
When dissolved in a liquid or melted, giant ionic structures can conduct electricity as the ions are free to move.