Definition of Stereoisomerism

Compounds/molecules that have some connectivity but different arrangements of atoms in space, so those compounds posses this situation is called stereoisomer and this phenomenon is said to be stereoisomerism.

OR

Stereoisomerism is caused by different arrangements of atoms or groups in Space.. This phenomenon is known as stereo isomerism.

Stereo=space
Isomerism=same molecular formula but differ in chemical/physical properties.

Stereoisomerism is exhibited by such compounds which have same structural formula but differ in configuration.

The term configuration refers to three dimensional arrangements of atoms, that characterize a particular compound.

Types of Stereoisomerism:

There are two types of stereo-isomerism:
1= Geometrical isomerism (cis-trans isomerism)
2= Optical isomerism

Geometrical Isomerism:

Those compounds having same molecular formula but a different geometric configuration as when atom or groups of atoms are attached in different special arrangements on either side of a bond or ring are said to be geometrical isomers and the phenomenon is known as geometrical isomerism.

Optical Isomerism:

It is a type of stereoisomerism, in which an optically active compounds can exist in two isomeric form which rotate plane-polarised light in opposite direction. These are called optical isomers and phenomenon is said to be optical isomerism.