Lab and analysis
Molecular formula
Definition
The number of atoms of each element in a molecule, such as C2H6O for ethanol.
Chemical databases write formulas in Hill order: carbon first, then hydrogen, then the other elements in alphabetical order. Compounds without carbon are written fully alphabetically.
Different compounds can share a formula. Ethanol and dimethyl ether are both C2H6O, so a formula alone does not identify a product. Use the CAS number or structure to be sure.
Related terms
- Molecular weight (molar mass)The mass of one mole of a substance in grams per mole, calculated from its formula and standard atomic weights.
- CAS registry number (CAS RN)A unique numeric identifier assigned by the Chemical Abstracts Service to a chemical substance, such as 7732-18-5 for water.
- SMILESA line notation that writes a chemical structure as a short text string, such as CCO for ethanol.