1.1. Understanding the history of quantum chemistry and mechanics

Knowing the development of quantum chemistry during the early part of the 20th century is important in order to understand how the postulates of quantum mechanics were discovered. It will also help you grasp the major approximations that have enabled us to achieve scientific milestones. We will mention concepts that will be discussed and described in later chapters of the book, so don't be concerned if you don't understand what the ideas mean or imply. We want to simply start using the terminology of quantum concepts to give some context to the five postulates of quantum mechanics presented in the rest of the book.

Figure 1.2 – Robert J. Oppenheimer – Ed Westcott (U.S. Government photographer), Public domain, via Wikimedia Commons

Quantum mechanics has been a disruptive topic of conversation in the scientific community for just over a century. The most notable controversy...