All carbohydrates have the basic chemical structure of CH2O. The differences lie in the number of times that basic structure is repeated, i.e. C6H12O6, the chemical formula of glucose.

Other compounds can have the same chemical formula however, the way the molecules are linked to each other is different. The difference gives them each unique biochemical characteristics.  Examples of this is that glucose and fructose both have the same formula but act slightly differently in the body.

Carbohydrates can be broken down in to different categories based on the number of simple sugars linked within the molecule. The carbohydrate classifications are monosaccharides, oligosaccharides, and polysaccharides.