Atomic charges, valencies and bond orders in six H-bonded systems, (H2O)2, (HF)2 and HnFn+1- (n = 1 to 4) have been calculated using 4-31G, 6-31G* and 6-31G** (only in the case of (HF)2 and HF2-) basis sets and employing definitions based on Mulliken and Löwdin SCF density matrices. The definitions based on the former and the 6-31G* basis set are found to give results in conformity with the classical valence theory. The covalent bonding is highly exaggerated by the alternative definitions based on the Löwdin density matrix. The H-bond formation is found to be accompanied by decrease in total valency, and the valency and atomic charge of bridging hydrogen. A clear distinction between normal and strong H-bonding can be made on the basis of bond order and overlap population of the intermolecular HX (X = F or O) bonds and the amount of charge transferred from the proton acceptor to the donor molecule. © 1987.