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Account for the difference in bond angle between water (104.5°) and methane (109.5°). - Leaving Cert Chemistry - Question g - 2008
Question g
Account for the difference in bond angle between water (104.5°) and methane (109.5°).
Worked Solution & Example Answer:Account for the difference in bond angle between water (104.5°) and methane (109.5°). - Leaving Cert Chemistry - Question g - 2008
Step 1
Lone pairs of electrons in water
Answer
Water has two lone pairs of electrons that occupy space around the oxygen atom. These lone pairs exert greater repulsion against the bonding pairs of electrons compared to the bonding pairs in methane, which has no lone pairs. This is due to the fact that lone pairs are positioned closer to the nucleus and have a higher electron density, leading to stronger repulsion.
Step 2
Greater repulsion in water
Answer
The greater repulsion from the lone pairs pushes the hydrogen atoms closer together, resulting in a bond angle of 104.5°. In methane, the absence of lone pairs allows for a more symmetrical arrangement of the hydrogen atoms, leading to the ideal tetrahedral bond angle of 109.5°.