Why is the bond angle in a water molecule (H_2O) less than the bond angle in a methane molecule (CH_4)?

• A. Because water forms a linear molecular geometry, resulting in a smaller bond angle.
• B. Because the hydrogen atoms in water are larger than the hydrogen atoms in methane, causing a smaller bond angle.
• C. Because water has two lone pairs on the oxygen atom, which repel the bonding pairs more strongly and decrease the bond angle.
• D. Because methane has a double bond between carbon and hydrogen, increasing its bond angle.

Answer: (C)

Verified step by step guidance

1. Identify the molecular geometries of water (H\_2O) and methane (CH\_4). Water has a bent shape due to two lone pairs on oxygen, while methane has a tetrahedral shape with no lone pairs on carbon.
2. Recall that bond angles in molecules are influenced by the repulsions between electron pairs around the central atom, according to the VSEPR (Valence Shell Electron Pair Repulsion) theory.
3. Understand that lone pairs of electrons occupy more space than bonding pairs because lone pairs are localized closer to the central atom, causing greater repulsion.
4. Recognize that in water, the two lone pairs on oxygen repel the bonding pairs of electrons more strongly, pushing the hydrogen atoms closer together and reducing the bond angle from the ideal tetrahedral angle of 109.5°.
5. In methane, there are no lone pairs on carbon, so the bonding pairs repel each other equally, maintaining the larger tetrahedral bond angle of approximately 109.5°.