In chemistry, isomers (/ˈaɪsəmərz/; from Greek ἰσομερής, isomerès; isos = "equal", méros = "part") are compounds with the same molecular formula but different structural formulas. Isomers do not necessarily share similar properties, unless they also have the same functional groups. There are many different classes of isomers, like stereoisomers, enantiomers, geometrical isomers, etc. (see chart below). There are two main forms of isomerism: structural isomerism and stereoisomerism (spatial isomerism).