Using VSEPR, predict the shapes of ammonia and water and explain lone-pair effects.

• A. NH3: trigonal pyramidal (3 bonding, 1 lone pair) ~107°; H2O: bent (2 bonding, 2 lone pairs) ~104.5°
• B. NH3: tetrahedral; H2O: linear
• C. NH3: seesaw; H2O: trigonal planar
• D. NH3: linear; H2O: square planar

Answer: (A)

VSEPR shows that the arrangement of electron pairs around a central atom determines molecular shape, and lone pairs occupy more space than bonding pairs, pushing bonding pairs closer together and changing angles.

In ammonia, nitrogen has three N–H bonds and one lone pair, giving four electron domains around N. The electron-domain geometry is tetrahedral, but the presence of the lone pair slightly compresses the bonding pairs, yielding a trigonal pyramidal shape with a bond angle of about 107 degrees.

In water, oxygen has two N–H bonds and two lone pairs, also giving four electron domains. The two lone pairs repel each other and the bonding pairs, producing a bent shape with a bond angle of about 104.5 degrees.

These results match the described shapes and angles: NH3 is trigonal pyramidal with ~107°, and H2O is bent with ~104.5°. The other options miss the correct combination of bonding vs. lone pairs and the resulting angles.