How are covalent network structures different from covalent molecular structures?

Covalent network structures are continuous 3D structures, while covalent molecular structures are discrete molecules.

Covalent network structures and covalent molecular structures are two different types of structures that can be formed by covalent bonds. Covalent bonds are formed when two atoms share a pair of electrons. This type of bond is typically found in non-metal elements.

Covalent network structures, also known as giant covalent structures, are formed when each atom is covalently bonded to several other atoms, creating a continuous three-dimensional network. This structure is not made up of individual, separate molecules, but rather a large, interconnected network of atoms. Examples of substances with covalent network structures include diamond (where each carbon atom is bonded to four other carbon atoms) and silicon dioxide (where each silicon atom is bonded to four oxygen atoms). For more details, see Giant Covalent Structures.

On the other hand, covalent molecular structures are formed when atoms are covalently bonded together to form discrete molecules. These molecules are then held together by intermolecular forces, which are weaker than the covalent bonds within the molecules. Examples of substances with covalent molecular structures include water (H2O), where each oxygen atom is bonded to two hydrogen atoms, and carbon dioxide (CO2), where each carbon atom is bonded to two oxygen atoms. You can learn more about the nature of these bonds in Polar and Non-Polar Covalent Bonds.

The difference in structure between covalent network structures and covalent molecular structures leads to different physical properties. Covalent network structures are typically very hard, have high melting and boiling points, and do not conduct electricity. This is because the strong covalent bonds throughout the entire structure require a lot of energy to break. In contrast, covalent molecular structures are typically softer, have lower melting and boiling points, and can sometimes conduct electricity. This is because the intermolecular forces between the molecules are weaker than the covalent bonds within the molecules, and thus require less energy to break. For a deeper understanding of these differences, refer to Simple Molecular Structures.

IB Chemistry Tutor Summary: Covalent network structures are vast 3D networks formed by atoms bonded continuously to others, making them hard and with high melting points, like diamond. Covalent molecular structures consist of distinct molecules, like water, making them softer with lower melting points. The key difference lies in their atomic bonding and the resulting physical properties.