Isomerization

Isomerization is a thing that happens to molecules and parts of molecules.
Isomerization is when a molecule or part of a molecule changes shape but still has the same number of each kind of atom. The atoms change places, but they do not go away. No new atoms come.
For example, when a ketose group changes to an aldose group, that is isomerization because both groups are -C2H3O2. They have two carbon atoms, three hydrogen atoms, and two oxygen atoms. In the ketose group, the first carbon has a double bond to an oxygen and a single bond to the other carbon. In the aldose group, the second carbon has the double bond to the oxygen, and the hydrogen atoms are in different places. But they both have the same number of each kind of atom.