Hill-System

The Hill - system (also called Hill cal System) is a rule that specifies the order of the element symbols in chemical formulas.

Definition

The sum formula of a compound is written in the order of C, H and all other elements in alphabetical order. For compounds without carbon, the arrangement is strictly alphabetical, the hydrogen is then queued. Isotopes abbreviations such as D and T are treated as separate elements and sorted accordingly.

Sort by empirical formulas

For a lexicographic order the atomic frequencies are numerically in ascending order (C1, ..., C9, C10, ... instead of C1, C10, ..., C2, ...).

History

The Hill System is applied by Edwin A. Hill in 1900 at the U.S. Patent Office.

Examples

BH3, BaCl2, CH4, CHNaO3, ClNa, C2H4, C2H4O2, C2H6, HOT

Not to be confused with the sum formulas according to the Hill system, the semi- structural formulas are also commonly used. For example, the empirical formula of the Hill system for methanol CH4O, while the semi- structural formula is CH3OH. In this example, the characteristic of alcohols OH group jumps at the half structural formula clearer eye.

Applications

The Hill system is used by major scientific literature databases and referencing substance or reaction indices used (eg Chemical Abstracts, Beilstein 1958 ) as stringing aid to the formula tab.