How does the presence of lone-pair electrons affect the bond angles in a molecule?

• A. Lone-pair electrons always result in bond angles of 120 degrees.
• B. Lone-pair electrons have no effect on the bond angles.
• C. Lone-pair electrons increase the bond angles compared to the ideal geometry.
• D. Lone-pair electrons decrease the bond angles compared to the ideal geometry.

Answer: (D)

Verified step by step guidance

1. Understand that lone-pair electrons are pairs of valence electrons that are not involved in bonding and occupy space around the central atom.
2. Recall that electron pairs, both bonding and lone pairs, repel each other according to the VSEPR (Valence Shell Electron Pair Repulsion) theory, which helps predict molecular shapes and bond angles.
3. Recognize that lone pairs repel more strongly than bonding pairs because lone pairs are localized closer to the central atom, causing greater repulsion.
4. Because of this stronger repulsion, lone pairs push the bonding pairs closer together, which results in a decrease in the bond angles compared to the ideal geometry where only bonding pairs are considered.
5. Therefore, the presence of lone-pair electrons decreases the bond angles relative to the ideal bond angles predicted for the molecule's electron pair geometry.