Explain the difference between a molecule and a crystal lattice.

A molecule is a group of atoms bonded together, while a crystal lattice is a repeating pattern of atoms, ions or molecules.

A molecule is the smallest particle in a chemical element or compound that has the chemical properties of that element or compound. Molecules are made up of atoms that are held together by chemical bonds. These bonds form as a result of the sharing or exchange of electrons among atoms. The atoms of certain elements readily bond with other atoms to form molecules. Examples of such elements are oxygen and chlorine. The molecules of elements consist of one type of atom only. For instance, the oxygen molecule is made up of two oxygen atoms. To understand more about how molecules form and their structures, you can read about simple molecular structures.

On the other hand, a crystal lattice is a three-dimensional structure composed of a repeating pattern of atoms, ions, or molecules. This pattern is known as the unit cell. The unit cell is like the basic building block of the crystal lattice, and by repeating in three dimensions, it forms the crystal structure. The arrangement of atoms within the unit cell and the shape and size of the unit cell itself can vary, leading to different types of crystal lattices. For example, table salt (sodium chloride) forms a cubic lattice, where each sodium ion is surrounded by six chloride ions and vice versa. For a deeper understanding of how these structures are formed, see the page on lattice structures.

The key difference between a molecule and a crystal lattice lies in their structure and composition. A molecule is a discrete group of two or more atoms, whereas a crystal lattice is a large collection of atoms, ions, or molecules arranged in a highly ordered, repeating pattern. Furthermore, the properties of a molecule are determined by the types of atoms it contains and the way those atoms are arranged, while the properties of a crystal lattice are determined by the types of particles it contains, the arrangement of these particles, and the type of crystal lattice structure it forms. To explore how different types of atoms come together in these structures, refer to the explanation on the formation of ions.

IB Chemistry Tutor Summary: A molecule is a group of atoms connected by chemical bonds, forming the smallest unit with the compound's properties. In contrast, a crystal lattice is an organised, repeating 3D structure of atoms, ions, or molecules forming a unit cell. Molecules have specific atomic arrangements, whereas crystal lattices have ordered patterns that define their properties.