Monosaccharides, like disaccharides, are sweet, water soluble and crystalline.

Monosaccharides are classified by the number of carbon molecules they contain (triose, tetrose, pentose, hexose and heptose) and by the active group, which is either an aldehyde or a ketone. These are then combined, e.g. aldohexoses, ketotrioses.

Further, each carbon atom that supports a hydroxyl group (except for the first and last) is optically active, allowing a number of different carbohydrates with the same basic structure. For instance, galactose is an aldohexose, but has different properties from glucose because the atoms are arranged differently.

Examples include:

• trioses: glyceraldehyde and dihydroxyacetone
• tetroses: Erythrose
• pentoses: lyxose, ribose and deoxyribose
• hexoses : idose, glucose, fructose, and galactose
• heptoses:

(CH₂O)_n