Ball-and-stick models are three-dimensional representations used in chemistry to illustrate the structure of molecules. In these models, atoms are represented by balls, while the bonds between them are depicted as sticks. This visual aid helps to convey the arrangement of atoms in a molecule and the angles between bonds, making it easier to understand molecular geometry. These models are particularly useful for visualizing complex structures, such as those found in organic compounds or coordination complexes. By using ball-and-stick models, scientists and students can better grasp concepts related to molecular interactions, such as those involving covalent bonds and ionic bonds.