Valence

Abstract

IN an article on “Types of Valence” in Science for July 22 Dr. Irving Langmuir develops still further the views on this subject which are associated with his name. He points out that the term “valence” has been used to describe (1) positive valence, or the number of electrons an atom can give up; (2) negative valence, or the number of electrons an atom can take up; and (3) covalence, or the number of electrons an atom can share with its neighbours. He brackets the first two under the name of “electrovalence,” and accounts for them by the tendency to form a complete layer of 2, 8, 8, 18, 18, or 32 electrons (First postulate). The outer incomplete layer of electronegative elements, such as oxygen and the halogens, which tend to take up electrons, is distinguished as a sheath, and this term is used even when the atom has taken up electrons, so that the outer layer has become for the time a completed sheath in the negatively charged ion. The same term is also used in the case of the electropositive elements to describe the small excess of electrons which are lost when the atom becomes a positively charged ion.