The solid state of carbon dioxide (CO2) is classified as a molecular crystal.
In a molecular crystal, the molecules are held together by relatively weak intermolecular forces, such as van der Waals forces or hydrogen bonds, rather than strong covalent or ionic bonds. In the case of solid CO2, the molecules consist of carbon atoms double-bonded to two oxygen atoms, forming linear CO2 molecules. These molecules do not bond ionically or covalently to each other in a network structure, which is characteristic of ionic and covalent crystals, respectively.
The solid state of CO2 generally occurs at low temperatures and is commonly referred to as dry ice. Here, the CO2 molecules are closely packed together in a structure that is held by these weaker forces, maintaining the overall integrity of the solid while allowing for some flexibility in the molecular arrangement.