Chemical Structure describes both the molecular geometry and the chemical bonds which link individual atoms together. The molecular geometry refers to the spatial arrangement of individual atoms within a three dimensional space. Such arrangements are usually determined by the chemical bond which is present, and the valency of the composing atoms.
Chemical structures may vary depending on the type of atom, element, and chemical bond. For example, covalent bonds between atoms form molecular structures, while ionic bonds between ions form crystal lattices, where a specific pattern and symmetry is usually observed. In addition, most chemical structures can then interact with other chemical structures to form larger structures; thus, forming a hierarchy of structures.
By using the Valence Shell Electron Pair Repulsion (VSEPR) theory, the geometry of a molecule can be determined through the degree of electrostatic repulsion between electron pairs within the molecule. For example, methane with a chemical formula CH4 does not have any nonbonding electron pairs, so equal repulsion takes place between each C-H bond, causing the molecule to take the natural form of a tetrahedral in a three dimensional space. On the other hand, ammonia, with a chemical formula NH3, has one nonbonding electron pair, and so it repulses the three N-H bonds more strongly than a typical N-H electron pair, causing the molecule to take the shape of a thin triangle-based pyramid.
Molecular structures can be determined by a multitude of experimental methods, whether they are conducted independently or in conjunction. For example, X-ray crystallography can be used independently to determine the atomic and molecular structure of crystals, by recording the direction of diffracted X-ray beams. Thus, understanding chemical structures, whether they are molecular or crystalline is crucial for understanding different chemical phenomena.