The shape of a molecule is affected by the arrangement of electrons, but does not describe that arrangement. The “shape” of a molecule is how the outside atoms are arranged around the central atom. The lone pairs of electrons affect this arrangement, but are not part of it.
Herein, how do you predict molecular geometry?
- VSEPR Rules:
- Identify the central atom.
- Count its valence electrons.
- Add one electron for each bonding atom.
- Add or subtract electrons for charge (see Top Tip)
- Divide the total of these by 2 to find the total.
- number of electron pairs.
- Use this number to predict the shape.
How can you determine the molecular geometry of a molecule?
VSEPR PRINCIPLES: The repulsion between valence electron pairs in the outer shell of the central atom determines the shape of the molecule. You must determine the steric number (SN) — the number of bonding pairs and lone pairs about the central atom. Lone pairs repel more than bond bonding pairs.