bonds and connectivities in molecule?

[li guo hui <chenhua[ AT ]ms.dicp.ac.cn>]

Dear Netters:
 i would like to know what is the true definition of bond, this question can also
 be given in the following:
 given a file only including coordinates of atoms in molecule, there are not
 connectivities between atoms in molecule, just from
 this file how can i find the bonds or connectivities? using Van der walls radius
 or covalance radius of atoms or some results of
 population analysis from theoretical calcualtion?
 thank you
 Li Guo Hui
 State Key Laboratory of Molecular Reaction Dynamics
 Dalian Institute of Chemical Physics
 Liao Ning Province, P.R.China
 Mailing Address:
 Room 715
 Xing Hai Third Street, 59 #
 Sha He Kou District
 Dalian, Liaoning Province
 P.R.China, 116023