Isomerism
Isomerism is a phenomenon in which two or more compounds have the same chemical formula but different structural arrangements or spatial orientations. This means that isomers have the same number and types of atoms but differ in the way these atoms are connected or arranged in space.

Types of Isomerism
There are several types of isomerism, including structural isomerism, stereoisomerism, geometric isomerism, optical isomerism, and linkage isomerism. Each type of isomerism arises from different factors and leads to different variations in the spatial arrangement of atoms.

Optical Isomerism
Optical isomerism, also known as enantiomerism, is a type of stereoisomerism that arises due to the presence of a chiral center in a molecule. A chiral center is an atom that is bonded to four different groups, resulting in non-superimposable mirror images.

Explanation
In optical isomerism, compounds have the same chemical formula and the same types of bonds. However, they differ in their spatial arrangement, specifically the arrangement of substituents around the chiral center. This results in the formation of enantiomers, which are non-superimposable mirror images of each other.

To understand this concept better, consider the example of tartaric acid. Tartaric acid exists in two optical isomers: (+)-tartaric acid and (-)-tartaric acid. Both isomers have the same molecular formula, C4H6O6, and the same types of bonds. However, they differ in the arrangement of substituents around the chiral carbon atom.

In the case of tartaric acid, the chiral carbon is bonded to four different groups: two carboxyl groups and two hydroxyl groups. In the (+)-tartaric acid, the hydroxyl groups are arranged in a clockwise manner, while in the (-)-tartaric acid, they are arranged in a counterclockwise manner. These two isomers are non-superimposable mirror images and exhibit different physical and chemical properties.

Thus, optical isomerism is the type of isomerism that exhibits compounds with the same chemical formula and bonds but different spatial arrangement around a chiral center.