1. I shall provide few references to specific textbooks and other materials. Most of them have been out of print for two or more decades and many have even disappeared from public and institutional libraries. Some live on on the bookshelves of chemistry teachers of a certain age, but are pretty much unavailable to most readers of this chapter. (A few of them continue into their Nth edition, with minuscule morphing from one to the next while often accreting additional authors.) The conceptual basis for the content of the majority of textbooks currently available is imperceptibly different from that of the generation following Sputnik, so little is missed by not being able to access these predecessors.