Skeletal formulas are a simplified way of representing organic compounds. Instead of writing out all the carbon and hydrogen atoms, they are implied by corners, also called ‘vertices’, in the structure. See for example Figure 1. Only carbon and hydrogen can be omitted this way.

Benzene is a 6 membered carbon ring with 6 hydrogens and 3 carbon carbon double bonds. The structure of benzene can be drawn in 2 ways.The first structure has the carbon and hydrogen atoms written as their element symbol and bonds connect between the letters. The second drawing is the skeletal structure of benzene. This structure has no element symbols and no hydrogens are shown, instead, there is a regular hexagon. Each place the lines intersect each other is the location of a carbon atom. Double bonds are shown with 2 parallel lines between the atoms in both structures. Salicylic acid is a benzene ring with two side groups, a hydroxyl group, O H, and a carboxylic acid group, C O O H. The skeletal structure is similar to benzene but there are element symbols to show the double-bonded oxygen, O, and the two hydroxyl groups, O H.

Figure 1. The organic molecule benzene with all atoms drawn out (Structure A), and the simplified skeletal structure (Structure B), which is commonly used. The skeletal structure of salicylic acid with molecular formula C7H6O3(Structure C)

Skeletal structures are a great way to more clearly show important aspects like functional groups of an organic compound, see Figure 2 for the skeletal structure of salicylic acid. A combination of the two ways of drawing the structure can be used as well.