The valence of some atoms exceeds the largest default valence. In these cases, subvalence is reported as zero. Consider sodium perchlorate (NaClO 4 ). The chlorine atom has a bond order sum of seven (2 + 2 + 2 + 1). From Table , the only default valence for chlorine is one. Subtracting seven yields a negative number (-6). Therefore, the subvalence is reported as zero.