Q.Explain the trend in oxidation state of elements from nitrogen to bismuth.

Step 1. State group 15's oxidation states. Table 9.5: group oxidation state +5 (ns2np3, all five valence electrons used), other stable state +3 (or -3).

Step 2. Nitrogen and phosphorus (lighter members). For N, the group +5 state is genuinely accessible (e.g. N2O5, HNO3) and, along with +3 (NF3) and -3 (NH3), nitrogen shows the widest range of oxidation states of the group because it lacks d-orbitals and behaves differently from the rest (e.g. no NCl5/NF5, Problem 9.6). Phosphorus similarly shows a stable +5 (PCl5, H3PO4) alongside +3 (PCl3). …

Applying the general group-15 oxidation-state trend (Table 9.5, section 9.4.1) …

• Treating N and P identically to As/Sb/Bi; nitrogen in particular is a special case because it altogether lacks valence d-orbitals (so it cannot form a pentahalide at all), which is a …