Lewis formulas are structures that show the connectivity, or bonding sequence of the atoms, indicating single, double, or triple bonds. They should also show any formal charges and unshared electrons that might be present in the molecule. Additional examples of Lewis formulas follow.\
These examples were deliberately chosen because all three molecules shown have the same molecular formula, but different connectivities, or bonding sequences. Such substances are called structural isomers, or sometimes constitutional isomers.
Notice that only the first structure shows the unshared electrons of chlorine. In Lewis formulas of organic compounds, it is customary to omit the lone electron pairs on the halogens unless there is a reason to show them explicitly.
Lewis formulas are mostly used for covalent substances, but occasionally they also show ionic bonds that might be present in certain compounds.