In most amines, the nitrogen atom is sp3 hybridized, with a pyramidal structure and bond...

In most amines, the nitrogen atom is sp³ hybridized, with a pyramidal structure and bond angles close to 109°. In urea, both nitrogen atoms are found to be planar, with bond angles close to 120°. Explain this surprising finding. (Hint: Consider resonance forms and the overlap needed in them.)