Formula
Definition and meaning of Formula in chemistry.
Formula is a notation that represents the composition of a chemical substance using element symbols and numerical subscripts showing the ratio or exact number of atoms of each element present.
In more detail
Chemists use several kinds of formulas depending on the detail needed. An empirical formula gives only the simplest whole-number ratio of atoms (e.g., CH2O), a molecular formula gives the actual number of atoms in one molecule (e.g., C6H12O6), and a structural formula additionally shows how atoms are bonded and arranged in space. For ionic compounds, the formula is always an empirical (formula) unit, since ionic solids do not exist as discrete molecules but as extended lattices in a fixed ratio.
Key facts
| Field | General Chemistry |
|---|---|
| Main types | Empirical, molecular, structural |
| Example formula | H2O (water) |
| Ionic compounds use | Formula unit (simplest ratio) |
Glucose has the molecular formula C6H12O6, meaning each molecule contains 6 carbon, 12 hydrogen, and 6 oxygen atoms; its empirical formula, CH2O, shows the same atoms in their simplest 1:2:1 ratio.
Frequently asked questions
What is the difference between an empirical and a molecular formula?
The empirical formula shows the simplest whole-number ratio of atoms, while the molecular formula shows the actual number of atoms in one molecule; the molecular formula is always a whole-number multiple of the empirical formula.
Why don't ionic compounds have molecular formulas?
Ionic compounds form continuous three-dimensional lattices of alternating cations and anions rather than discrete molecules, so their formula (e.g., NaCl) represents only the fixed ratio of ions, called a formula unit.