Estimate of two general relationships between the number of atoms and the volumes of the unit cells of compounds containing only non-metallic p-block elements

Compounds with the general formula C a H b N c O d X x (where X=boron and/or a non-metallic element of the third to fifth period; b≥1; a, c, d, e... x≥0) have been studied using the Cambridge Structural Database as a source of data and a search tool. Two relationships between the volume (V) and the number of formula units (Z) in the unit cell have been established that account for the individual contributions of elements to the cell volume in terms of their element period number. The two improved relationships have 84.3 and 82.7% of entries, respectively, within the 10% error boundary, and they are more accurate than other expressions described in the literature