Group V.: N, trivalent and pentavalent, but divalent in nitric oxide; P, As, Sb, Bi, trivalent and pentavalent, the last being possibly divalent in BiO and BiC1 2.
Group VI.: 0, usually divalent, but tetravalent and possibly hexavalent in oxonium and other salts; S, Se, Te, di-, tetraand hexa-valent; Cr, di-, triand hexa-valent; Mo, W, di-, tri-, tetra-, pentaand hexa-valent.
Group VII.: H (?), monovalent; the halogens F, Cl, Br, I, usually monovalent, but possibly also triand pentavalent; Mn, divalent and trivalent, and possibly heptavalent in permanganates.
Group VIII.: Fe, Co, divalent and trivalent; Ni, divalent; Os, Ru, hexavalent and octavalent; Pd, Pt, divalent and tetravalent; Ir, tri-, tetraand hexa-valent.
In many cases it may be connected with basic oxygen, and the salt formation is assumed to involve the passage of divalent into tetravalent oxygen.