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For questions related to molecular formula, empirical formula, formula unit, representing the chemical proportions of atoms that constitute a particular chemical compound, molecule, ion, complex, crystal, etc. using chemical element symbols, numbers, and other symbols. NOT related to 'notation', 'composition', 'structure' or 'nomenclature'.

Definition:

Wikipedia

A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as parentheses, dashes, brackets, commas and plus (+) and minus (−) signs. These are limited to a single typographic line of symbols, which may include subscripts and superscripts. A chemical formula is not a chemical name, and it contains no words. Although a chemical formula may imply certain simple chemical structures, it is not the same as a full chemical structural formula. Chemical formulas can fully specify the structure of only the simplest of molecules and chemical substances, and are generally more limited in power than are chemical names and structural formulas.

The simplest types of chemical formulas are called empirical formulas, which use letters and numbers indicating the numerical proportions of atoms of each type. Molecular formulas indicate the simple numbers of each type of atom in a molecule, with no information on structure. For example, the empirical formula for glucose is $\ce{CH2O}$ (twice as many hydrogen atoms as carbon and oxygen), while its molecular formula is $\ce{C6H12O6}$ (12 hydrogen atoms, six carbon and oxygen atoms).

Applicability of the tag:

  • should be applied for questions related to molecular formula, empirical formula, formula unit of a crystal lattice. Its equally applicable for organic and inorganic compounds.
  • For representing a particular chemical compound (or its formula unit), molecule, ion, complex or other species, correctly according to IUPAC rules, when given a set of chemical elements taking care of their valencies and respective oxidation states and other necessary details.
  • This tag does NOT deal with the , or of the chemical species. Neither to be confused with of physical quantities related to chemistry or 'chemical composition' of a reagent. Again with special emphasis only on chemical formula.
  • This tag to some extent is loosely related to the usage of condensed-formula, nuclear notations; rigorousness depends on the user.

Further reading: