1. The problem statement, all variables and given/known data Prove that if bonding-pair repulsions were maximized in CH3X, then the sum of the bond angles would be 450°. 2. Relevant equations In a perfect tetrahedral molecule (e.g. methane), the sum of the bond angles is about 438 degrees (109.5° times 4). 3. The attempt at a solution Well, if the tetrahedron were flattened as to give us a trigonal planar base and one attachment sticking off perpendicular to the base, we would have three 90 degree bond angles. That's not very helpful in achieving the 450 degree sum. So I'm guessing that the base of the tetrahedron has been very nearly flattened. In addition, a sum of 450 degrees implies an average bond angle of 112.5 degrees. How do we go about proving this though? There are bent molecules with bond angles of approximately 112.5 degrees, and these approximate this tetrahedron - bent molecules have two lone pairs and lone pair/lone pair repulsion is rather great.