Question

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?

Answer 1

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

Step-by-step 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.

Answer 2

Because only the electrons groups on the central atom contribute to the repulsion.

Step-by-step explanation:

The geometry of a molecule is determined by the theory of the repulsion of the pairs of the electrons. This theory states that the electrons shared at the bonds and the lone pairs of electrons intend to be as far as possible, so the energy at the molecule will be the minimum. Because the terminal atoms are too far away in the molecule, the lone pairs in them don't affect the energy as the lone pairs of the central atom, so only these last are considered.