ABSTRACT
A metric is a standard measurement of some parameter or property. The acid dissociation constant is a metric of the propensity of a chemical substance to produce protons in aqueous solution. The bond dissociation energy is a metric of bond strength. The Celsius scale is a metric for temperature. Whenever a metric exists there is always a standardized scale associated with it that has de“ned units. It is important to know what the reference state is for that standardized scale. For example, the hydrogen electrode is the reference electrode against which the pH scale and oxidation potential scales are de“ned. A direct consequence of making up scales for things is ranking. In chemistry, it is more meaningful to talk about relative acidity than absolute acidity, for example. Hence, chemists ask the question, is substance A more or less acidic than substance B if the molecular structure of substance A has a particular kind of functional group in it?
