Introduction to Matter (Book)

Types of Matter

Molecules and Crystals

The smallest particle of a compound that still has the compound’s properties is a molecule. A molecule consists of two or more atoms that are joined together. For example, a molecule of water consists of two hydrogen atoms joined to one oxygen atom (see Figure below). You can learn more about molecules at this link:

Water is a compound that forms molecules. Each water molecule consists of two atoms of hydrogen (white) and one atom of oxygen (red).

Some compounds form crystals instead of molecules. A crystal is a rigid, lattice-like framework of many atoms bonded together. Table salt is an example of a compound that forms crystals (see Figure below). Its crystals are made up of many sodium and chloride ions. Ions are electrically charged forms of atoms. 

You can actually watch crystals forming in this video:

A crystal of table salt has a regular, repeating pattern of ions.