The formula alone may be used subsequently. To avoid ambiguity, it is preferable to spell out the word tungsten. However, if the word is used heavily within the same document, use of the symbol W saves time and space, and alleviates repetition. Isotopes may be written as carbon-14 or 14C. When written out, names of chemical elements and compounds are written in lowercase letters. The chemical symbols are capitalized as they appear in the periodic table of elements.
Many abbreviations use the same form whether plural or singular.
Most abbreviations do not end with a period. Exceptions include abbreviations that may be confused with a word, are personal titles, or traditionally end with periods. When an abbreviation that normally ends with a period appears at the end of a sentence, do not add a second period. Set off i.e. , e.g. , and etc. , as you would the full phrases they abbreviate. Both i.e. and e.g. should be immediately followed by commas.