What are the necessary conditions for formation of a Hydrogen Bond?

Usually Hydrogen bonds are associated with N,O,F as the atoms involved. In some cases OH---Cl bond is observed as in case of o-chlorophenol.


According to the updated IUPAC definition a Hydrogen bond can be formed between molecules having EN greater than hydrogen (which explains the H-bond in DCM(aq) and chloroform(aq)).


My first question is -How is the EN decided for concluding the formation of H-bond between two **General** atoms?
Is it the Pauling scale(defined for sp3 hybrids), or an application of Bent's Rule for determining s% in a bonded orbital.By General I mean not N,O, or F as the only participants and a definition that can be extended for C, Cl etc.


My second question is- Is it possible to quantitively determine the strength of a H bond with minimal data like EN between atoms , or at least sufficient to conclude the formation of a H-bond between them?


