MadSci Network: Chemistry
Query:

Re: What is the differance between an empirical formula and a molecular formula

Date: Mon Oct 25 11:00:31 2004
Posted By: Dan Berger, Faculty Chemistry/Science, Bluffton College
Area of science: Chemistry
ID: 1098317844.Ch
Message:

An empirical formula is the smallest whole-number ratio of the elements that make up a particular compound. A molecular formula is the actual number of each kind of atom that make up one molecule of a compound.

Obviously, if a compound doesn't have molecules of reasonable size, it can't have a molecular formula; for example, a diamond (empirical formula = C) is one big molecule.

Some examples of empirical and molecular formulas:
Substance Empirical formula Molecular formula
acetylene CH C2H2
benzene CH C6H6
oxygen O O2
ozone O O3
Senecialdehyde, a strongly-smelling irritant C5H8O C5H8O
Lineatin, an insect sex attractant C5H8O C10H16O2
Leukotriene B4, a bronchoconstrictor that plays a role in severe allergic reactions C5H8O C20H32O4

As you can see, two compounds with the same empirical formula can be quite different.

Dan Berger

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