Symbols for chemical elements shall be written in roman (upright) type. The symbol is not followed by a full-stop.
Examples:
: H He C Ca
Attached subscripts or superscripts specifying a nucleotide or molecule have the following meanings and positions:
* The nucleon number (mass number) is shown in the left superscript position (e.g., N)
* The number of atoms of a nucleotide is shown in the right subscript position (e.g., N)
* The proton number (atomic number) may be indicated in the left subscript position (e.g., Gd)
* If necessary, a state of ionization or an excited state may be indicated in the right superscript position (e.g., state of ionization Na)