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How does a molecular formula show the atoms in a molecule?

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representations of molecular structure — molecule Several methods of representing a molecule's structure. In Lewis structures, element symbols represent atoms, and dots represent electrons surrounding them. A pair of shared electrons (covalent bond) may also be shown as a single dash. The ball-and-stick model better illustrates the spatial arrangement of the atoms. For aromatic compounds, the Kekulé structure is common, in which each bond is represented by a dash, carbon atoms are implied where two or more lines meet, and hydrogen atoms are usually omitted. Bond-line formulas, similar to the Kekulé structure, are often used for complex nonaromatic organic compounds. Sugars are often drawn as Fischer projections, in which the carbon “backbone” is drawn as a straight vertical line, with carbon atoms implied where horizontal lines intersect the vertical one.

A molecular formula identifies the exact composition of a molecule by providing the total number of atoms of each element present in a single unit of a substance.12

Unlike an empirical formula, which only shows the simplest ratio of atoms, the molecular formula specifies the actual count of every atom in the molecule. For example, while both ethylene and propylene share the same empirical formula of ${CH}_{2}$ , their molecular formulas— $C_{2} H_{4}$ and $C_{3} H_{6}$ , respectively—clearly distinguish them by stating the precise number and kind of atoms contained in each. In instances where the simplest ratio is the actual composition, such as with water, the empirical and molecular formulas may be identical.2

While these formulas are essential for defining chemical composition, they do not illustrate the spatial arrangement or the specific chemical bonds between atoms; for that level of detail, structural formulas or projection formulas are used.2