Abegg's rule

Abegg's rule states the sum of the absolute values of the maximum positive and negative valence of an atom is often equal to eight.

Abegg’s rule is sometimes referred to as "Abegg’s law of valence and countervalence".
for a given chemical element (as sulfur) Abegg’s rule states that the sum of the absolute value of its negative valence (such as −2 for sulfur in H₂S) and its positive valence of maximum value (as +6 for sulfur in H₂SO₄) is often equal to 8.
The rule used a historic meaning of valence which resembles the modern concept of oxidation state in which an atom is an electron donor or receiver.

January 9, 1869 – April 3, 1910
Danish chemist, major work on chemical valence
Trained as organic chemist (student of August Wilhelm von Hofmann at the University of Berlin); but practiced physical chemistry with Friedrich Wilhelm Ostwald in Leipzig, Germany

Abegg, R. (1904). "Die Valenz und das periodische System. Versuch einer Theorie der Molekularverbindungen (The valency and the periodical system - Attempt on a theory of molecular compound)". Zeitschrift für anorganische Chemie 39 (1): 330–380. doi:10.1002/zaac.19040390125.
Lewis, Gilbert N. (1916-04-01). "THE ATOM AND THE MOLECULE". Journal of the American Chemical Society 38 (4): 762–785. doi:10.1021/ja02261a002.
Pauling, Linus (1960-06). The Nature of the Chemical Bond and the Structure of Molecules and Crystals; An Introduction to Modern Structural Chemistry. (3 ed.). Cornell University Press. ISBN 0-8014-0333-2.
http://en.wikipedia.org/wiki/Abegg%27s_rule
http://www.springerreference.com/docs/html/chapterdbid/206127.html
http://en.wikipedia.org/wiki/Richard_Abegg

ORGANIC SYNTHESIS INSIGHT