A chemical formula is a symbolic representation of the composition of a molecule.
The empirical formula shows merely the proportions of the atoms in the molecule, as found by chemical analysis, e.g., water H2), acetic acid CH2O. (The subscripts indicate the number of each atom if more than one.)
The molecular formula shows the actual number of atoms in the molecule, e.g., water H2O, acetic acid C2H4O2O2. The atomic symbols are sometimes grouped to give some idea of the molecular structure, e.g., acetic acid CH2COOH.
The space formula shows the arrangement of the atoms and bonds in three-dimensional space, and so distinguishes between stereoisomers; it may be drawn in perspective or represented conventionally.
Loosely-associated compounds, such as ligand complexes, are often shown with a dot, e.g., copper (II) sulfate pentahydrate, CuSO4.5H2O. Special symbols are sometimes used for common groups and ligands, e.g., ethyl Et, phenyl Ph.