This historical review traces the origins of the Kimball free-cloud model of the chemical bond, otherwise known as the charge-cloud or tangent-sphere model, and the central role it played in attempts to reform the introductory chemical curriculum at both the high school and college levels in the 1960s. It also critically evaluates the limitations…

In response to a reader query, this article traces the origins of the ionic-radius ratio rules and their incorrect attribution to Linus Pauling in the chemical literature and to Victor Goldschmidt in the geochemical literature. In actual fact, the ionic-radius ratio rules were first proposed within the context of the coordination chemistry…

Presents two illustrations and accompanying text about carbon dioxide toxicity taken from an 1886 textbook. (MLH)

Discusses major events leading to the development of the octet rule. Three conclusions based on the work of Mendeleev, Abegg, Thompson, Kossel, Lewis, and Langmuir are considered as is the debate over the rule's validity. (JN)