Q1(a)(i). Bond angle of F₂O smaller than that of H₂O

Answer in brief

Both are bent AX₂E₂ molecules. F is more electronegative than O, so the O–F bonding pairs are drawn away from O; they repel each other less and the lone pairs close the angle to 103.3°. In H₂O the bonding pairs sit near O and the angle stays at 104.5°.

Key points

• In both molecules O has four electron pairs (two bond pairs, two lone pairs) in a tetrahedral arrangement: the molecule is bent, and lone-pair repulsion closes the angle below 109.5°.
• The angle then depends on how close the bonding pairs lie to O. Electronegativities (Allen scale, Miessler): F 4.19, O 3.61, H 2.30 (Pauling: 3.98, 3.44, 2.20).
• H₂O: O is more electronegative than H, so the O–H bonding pairs are held close to O. Near the centre they repel each other strongly and resist the lone pairs: H–O–H=104.5°
• F₂O: F is more electronegative than O, so the O–F bonding pairs are pulled out towards F. There is less electron density near O, bp–bp repulsion is smaller, and the lone pairs push the bonds closer: F–O–F=103.3°