A Python dictionary of atomic weights in Decimal objects.
Measurements come from IUPAC's Comission on Isotopic Abundances and Atomic Weights (IUPAC-CIAAW). This dictionary uses measurements from IUPAC-CIAWW's Atomic weights of the elements: Review 2000.
See ciaaw.org for updated measurements.
Per IUPAC-CIAAW, only elements with stable isotopes are included.
Using an element's chemical symbol (e.g., "H") as a key returns a sub-dictionary. The sub-dictionary contains two keys (1) standard for the atomic weight and (2) abundant for the atomic mass of the element's most-abundant isotope.
Standard atomic weight or atomic weight refers to the weighted average mass of an element's isotopes.
The most-abundant isoptope of an element is important for high resolution mass sepctromentry. For biologically relevant molecules, an elements most-abundant isotope is usually the lightest isotope. An exact mass can be calculated from these values.
Tab characters are used as whitespace in the dictionary to simplify regex manipulation.
A for loop iterates through all chemical element's weights.
Care should be taken when applying these measurements. Standard weights may not be applicable to high-resolution mass spectrometry. Some elements have multiple stable isotopes with similar relative abundances. For instance, 50.69% of Bromine is 79Br and the other 49.31% is 81Br. Chlorine's isotope abundances are particularily relevant to biochemists: 75.76% 35Cl (34.9688527 71 Da) and 24.24% 37Cl (36.96590260 Da).