The interactions of primary, secondary, and tertiary alkylamines with the Si(001) surface have been investigated using x-ray/ultraviolet photoelectron spectroscopy, Fourier transform infrared spectroscopy and scanning tunneling microscopy. Experimental and computational results show that alkylamines bond to the surface through the nitrogen atom. Primary alkylamines such as hexylamine bond to the surface by breaking only one N-H bond. Secondary alkylamines such as dimethylamine and N-methylpentylamine cleave only the N-H bond, leaving the N-C bonds intact. Tertiary alkylamines, such as trimethylamine and NN-dimethylbutylamine, can form stable dative-bonded adducts on the surface that are characterized by very high N(1s) binding energies of 402.2 eV The ability to form dative-bonded adducts between tertiary alkylamines and Si(001) stems from the capability of electron transfer from nitrogen to the surface. Our results show that this charge exchange controls the propensity for N-H vs N-C bond cleavage.