Molecules that have the same chemical formula (same numbers of each atom) but different three-dimensional shapes are called see concept 4.2 (page 60)

            Molecules that have the same chemical formula (same numbers of each atom) but different three-dimensional shapes are called Stereoisomers.

Explanation:

                   Stereoisomerism is a phenomenon in which molecules have same molecular formula but have different arrangement of atoms or group of atoms in space. It is further classified as;

                      i) Geometrical Isomerism:

                                                                In this class of isomerism the groups or atoms about the double bond occupies different region in space. It is also called as cis-trans isomerism.

                      ii) Optical Isomerism:

                                                          In this class the molecules having same molecular formula differ in their interaction towards plane polarized light.