2. Определите валентность по формулам: CaCl2, HF, Na2S, NO2, Cu2O, PbS2, P2O5, SO3, Cl2O7.

1. CaCl2 (Ca-II, Cl-I), HF (H-I, F-I), Na2S (Na-I, S-II), NO2 (N-IV, O-II), Cu2O (Cu-I, O-II), PbS2 (Pb-IV, S-II), P2O5 (P-V, O-II), SO3 (S-VI, O-II), Cl2O7 (Cl-VII, O-II).