where m corresponds to the respective bond order (e.g. 7 for Xp -7dv, encompassing m + 1 atoms) for which fragments (ch = chains or p = paths) within the molecule are counted, taking into account all A heavy atoms. For each fragment, c m i is computed, where p k represents the number of sigma or valence electrons and h k the number of bonded hydrogens of each atom k within the corresponding subgraph .