Key concepts in chemistry Study Guide

Simple molecular covalent compounds, like water or carbon dioxide, are made up of individual molecules held together by strong covalent bonds. However, the forces *between* these separate molecules, known as intermolecular forces, are relatively weak. These weak intermolecular forces explain why these compounds typically have low melting and boiling points, as only a small amount of energy is needed to overcome them and separate the molecules. Furthermore, these compounds do not conduct electricity because they do not have free-moving charged particles (ions or delocalised electrons) to carry an electrical current. The electrons are localised within the covalent bonds between atoms.

Carbon is a unique element due to its ability to form various structures, known as allotropes. Among the most well-known are diamond and graphite, which are both examples of giant covalent substances. In giant covalent structures, many atoms are held together by strong covalent bonds throughout the entire structure, rather than forming discrete molecules. This extensive bonding network is responsible for their distinct physical and chemical properties. Despite both being made solely of carbon atoms, the arrangement of these atoms differs significantly in diamond and graphite, leading to vastly different characteristics.