Abegg's rule

Abegg's rule, proposed by the chemist Richard Abegg in 1904, states that the difference between the maximum positive and maximum negative valence an element can show is frequently eight. It applies an older valence concept resembling the modern idea of oxidation states, in which atoms are treated as donating or accepting electrons; for sulfur, for example, its negative valence of minus two in hydrogen sulfide and its maximum positive valence of plus six in sulfuric acid sum to eight, the pattern the rule describes. The relationship is also known as Abegg's law of valence and countervalence.