In Pauling's description (4) of a metallic bond, the bond number is defined as the number of bonding electrons
divided by the number of neighbors to which the specific atom bonds.
Current interests include low-temperature residual electron density studies to examine bonding electrons
and non-bonding electron pairs; crystal packing with an emphasis on the factors that influence the selection of the particular packing arrangements in a sequence of related compounds; packing dynamics in a crystal and its variation with changing temperature; hydrogen bonding studies and X-ray crystal structure determinations that look intriguing, interesting, odd, or that are needed by colleagues.
In the standard two-dimensional view, the table's row (horizontal) dimension specifies the number and arrangement of bonding electrons that occupy an element's outer, or valence, electronic shells, the region of all chemical bonding.
These values correspond to the amounts of energy required to remove bonding electrons from an atom's valence electron shells.