In the context of molecular geometry, how does adding an atom to a central atom affect the positions of existing atoms or lone pairs around it?

• A. It increases electron repulsion, causing existing atoms or lone pairs to adjust their positions to minimize repulsion.
• B. It decreases electron repulsion, so existing atoms or lone pairs move closer together.
• C. It has no effect on the positions of existing atoms or lone pairs.
• D. It always forces existing atoms or lone pairs into a linear arrangement.

Answer: (A)

Verified step by step guidance

1. Understand that molecular geometry is determined by the arrangement of electron groups (bonding atoms and lone pairs) around a central atom to minimize electron repulsion.
2. Recall the Valence Shell Electron Pair Repulsion (VSEPR) theory, which states that electron groups repel each other and arrange themselves as far apart as possible to minimize repulsion.
3. When a new atom (bonding group) is added to the central atom, the total number of electron groups increases, which increases the overall electron repulsion around the central atom.
4. Because of this increased repulsion, the existing atoms and lone pairs must adjust their positions to maintain the greatest possible distance from each other, thereby minimizing repulsion.
5. This adjustment changes the molecular geometry by altering bond angles and positions of atoms and lone pairs, but it does not necessarily force a linear arrangement unless dictated by the number of electron groups.