Third-law entropies, although they come purely from thermal measurements, tell us something about molecular structure if we know how to interpret them. These trends in entropies are summarized below, and the entropies of the pure elements as they ordinarily are encountered at room temperature are listed on the periodic table on the right. All of the trends in this table now should be understandable. Although entropy originally began as a rather abstract concept involving heat, it has a definite and visualizable meaning. Entropy is a direct and quantitative measure of disorder.