1、How is base strength related to the availability of the electron-pair?

1.Base strength depends on the ability of the basic site (which always has an unshared electron pair) to accept a proton.This ability depends on the charge in an anion or electron density in a molecular base.For species with an identical charge,dispersal or delocalization of the electrons from the basic site to other parts of the molecule results in decreased electron density and decreased base strength.
2.molecules having atoms with high electron density are called nucleophiles or electron donors.
molecules having atoms with low electron density are called electrophiles or electron-acceptors.
3.The atom in question,called a nucleophilic site,may be the negative (delta -) end of a polar covalent bond,have an unshared electron pair,or be part of a pi bond.It may also have a combination of these features.
The atom in question,called an electrophilic site,may be capable of taking on more valence electrons or be the positive (delta +) end of a polar bond.
4.Coordinate covalent bonding,Nu:+ E -> Nu:E