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How do chemical formulas show the types and relative numbers of atoms in a compound?

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Two diagrams show the three-dimensional structure of a methane molecule: panel A uses a ball-and-stick model with a central carbon atom connected to four hydrogen atoms in a tetrahedral arrangement, while panel B illustrates the bond angle of 109.5 degrees and bond length of 1.09 angstroms between carbon and hydrogen atoms. — chemical compound Methane, in which four hydrogen atoms are bound to a single carbon atom, is an example of a basic chemical compound. The structures of chemical compounds are influenced by complex factors, such as bond angles and bond length.

Chemical formulas represent the composition of chemical compounds by using symbols and numbers to identify the constituent parts of a substance.1

Types of Atoms: Each chemical element is represented by a unique symbol, such as C for carbon, H for hydrogen, or O for oxygen. These symbols indicate which elements are present in the compound.12
Relative Numbers of Atoms: Subscripts are used to denote the relative number of atoms of each element present. For example, in the formula for water, H₂O, the subscript "2" indicates two atoms of hydrogen for every one atom of oxygen. If an element has only one atom in the formula, no subscript is written.12

While empirical formulas provide the simplest ratio of atoms, molecular formulas specify the exact number of every atom in a molecule. Other forms, such as structural formulas, further clarify how these atoms are connected by chemical bonds.1