The inversion of nitrogen requires a change of hybridization. 

(a) What is the approximate energy difference between pyramidal nitrogen (sp³ hybridized) and trigonal planar nitrogen (sp² hybridized) in ammonia and simple amines? 

(b) Compare the nitrogen atom in ammonia with the carbon atom in each of the following species: methyl cation, methyl radical, and methyl anion. Compare the most stable geometries and the hybridizations of each of these species. Using fundamental notions of orbital energies and bond strengths, explain the similarities and differences among them.