In determining electron geometry, why do we consider only the electron groups on the central atom? why don't we consider the electron groups on terminal atoms?

The shape of a molecule is dependent on the arrangement of the terminal atoms around the central atom.

Explanation:

In the VSEPR, the terminal atoms are treated as electron pairs arranged around the central atom in such a way as to minimize repulsion between them. The number of terminal atoms around the central atom are counted as the electron pairs. Our major concern is how these electron pairs arrange themselves around the central atom.