Chemists use a variety of notations to describe and
summarize the atomic constituents of compounds.
These notations, which include empirical, molecular, and
structural formulas, use the chemical symbols for the
elements along with numeric values to describe atomic
Empirical formulas are the simplest form of notation.
They provide the lowest whole-number ratio between the
elements in a compound.
Unlike molecular formulas, they do not provide
information about the absolute number of atoms in a
single molecule of a compound.
The molecular formula for a compound is equal to, or a
whole-number multiple of, its empirical formula.
An empirical formula lacks any structural information
about the positioning or bonding of atoms in a molecule.
It can therefore describe a number of different
structures, or isomers, with varying physical properties.
For butane and isobutane, the empirical formula for both
molecules is C2H5, and they share the same molecular
One structural representation for butane isCH3CH2CH2CH3, while isobutane can be described using
the structural formula3CH. Butane.
Empirical formulas can be determined using mass
A CHN analyzer can be used to find the mass fractions of
carbon, hydrogen, oxygen, and other atoms for a sample
of an unknown organic compound.
Once the relative mass contributions of elements are
known, this information can be converted into moles.