Properties of Covalent Substances Covalent bonds are very strong. Substances with covalent bonds can form small molecules or giant structures These two types of substances have different properties.

What are simple covalent structures? Covalent molecules that contain only a few atoms are called simple covalent structures. weak bonds between molecules strong bonds within molecules Most substances that contain simple covalent molecules have low melting and boiling points and are therefore liquids or gases at room temperature, e.g. water, oxygen, carbon dioxide, chlorine and hydrogen. Why? The covalent bonds within these molecules are strong but the bonds between molecules are weak and easy to break.

What are giant covalent structures? In some substances, such as sand, diamond and graphite, millions of atoms are joined together by covalent bonds. All the bonds are covalent, so giant covalent structures have very high melting and boiling points, and are usually hard. The covalent bonds in these substances do not form molecules but vast networks of atoms called giant covalent structures.

Key Points Simple Covalent Structures- Low Melting and Boiling points because of the weak forces between neighbouring molecules. Giant Covalent Structures- High melting and boiling points because all the atoms are joined to atoms by strong covalent bonds.

What you need to know about In your specification you are required to know about Diamond and graphite. Both are giant covalent structures, therefore both have high boiling and melting points.

What is the structure of diamond?

What is the structure of graphite?