Lewis acids and bases studied chemical bonding. In 1923, Lewis wrote "An acid substance is one which can employ an electron lone pair from another molecule in completing the stable group of one of its own atoms." The Brønsted–Lowry acid–base theory was published in the same year. The two theories are distinct but complementary. A Lewis base is also a Brønsted–Lowry base, but a Lewis acid doesn't need to be a Brønsted–Lowry acid. The classification into hard and soft acids and bases (HSAB theory) followed in 1963. The strength of Lewis acid-base interactions, as measured by the standard enthalpy of formation of an adduct
Internet-related prefixes as a cultural reference to the rising popularity at that time of the prefix in product names. The word "virtual" is used in a similar way to the prefixes above, but it is an adjective instead of a prefix. For example, it is used in the terms "virtual reality", "virtual world", and "virtual sex". These prefixes are productive. Michael Quinion notes that most of these formations are nonce words that will never be seen again. He writes that new terms such as "e-health" are unneeded; in this case "telemedicine" already exists to describe the application of telecommunications to medicine. He