posted by Joseph .
NH2-, NH3, and NH4+ have H-N-H bond angles of 105, 107 and 109. Explain this variation in bond angles.
The difference lies in the number of lone pair electrons. Lone pair electrons take up more room than paired electrons; therefore, the atoms "on the other side" of the lone pair have less room and the angles are smaller. The NH4^+ has no unpaired electrons and the angle is that of a tetrahedral angle.