Alkyl amines characteristically feature tetrahedral nitrogen centers.  C-N-C and C-N-H angles approach the idealized angle of 109°.  C-N distances are slightly shorter than C-C distances.  The energy barrier for the nitrogen inversion of the stereocenter is about 7 kcal/mol for a trialkylamine. The interconversion has been compared to the inversion of an open umbrella into a strong wind.
Amines of the type NHRR and NRR′R″ are chiral: the nitrogen center bears four substituents counting the lone pair. Because of the low barrier to inversion, amines of the type NHRR cannot be obtained in optical purity.  For chiral tertiary amines, NRR′R″ can only be resolved when the R, R, and R″ groups are constrained in cyclic structures such as N'-substituted aziridines (quaternary ammonium salts are resolvable).