The bond angle in a molecule of methane, ammonia and water decreases in the order 109.5, 107 and 104.5 degrees because
- A. the central atoms become larger in that order
- B. the number of lone pairs on the central atom increases from zero to one to two
- C. the bonds become more ionic
- D. the molecules become heavier
Explanation
Each additional lone pair exerts stronger repulsion than a bond pair, squeezing the remaining bonds closer together, so the angle falls by roughly two and a half degrees for each one added. The underlying arrangement of four electron regions is tetrahedral in all three cases. This trio is the classic demonstration that lone pairs must be counted but are not seen in the shape.
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