Common Chemical Formulas

A chemical formula expresses the chemical composition of a compound using chemical symbols. This is done by assigning special meaning to subscripts and superscripts. Some molecules are so similar that they share the same chemical formula. Therefore, different forms of chemical formulas have been developed to aid in this distinction, including pictorial representation.

Like E=mc^2 in physics, some chemical formulas are known all over the world. H2O, CO2 and HCl are probably the most recognized.

Everyday Substances

Of everyday substances, the symbol for water, H2O, is probably the most known. Table salt (NaCl) may be the next, far ahead of the related base sodium hydroxide (NaOH). Ammonia (NH3) and methane (CH4) are well-known as a cleanser and a gaseous fuel respectively. Table sugar, or glucose, is C6H12O6. And air is a mixture of several gases, mostly diatomic nitrogen gas (N2), diatomic oxygen gas (O2) and a little carbon dioxide (CO2), plus some other trace gases. Carbon monoxide (CO), although widely known, is not an everyday substance, since it is lethal in enclosed areas. Hydrogen peroxide, used as a disinfectant and to bleach hair, is H2O2. C9H8O4 is the chemical formula for aspirin.

Common Acids

Some common acids and their chemical formulas are as follows: hydrochloric acid (HCl); nitric acid (HNO3); hydrocyanic acid (HCN); perchloric acid (HClO4); sulfuric acid (H2SO4); and carbonic acid (H2CO3).

How readily an acid transfers a proton to water determines the strength of an acid. One may presume that the acids above with two hydrogens to give up are the strongest. Sulfuric acid is indeed a strong acid, but perchloric acid is the strongest listed here. Carbonic acid can be either a weak or a strong acid, depending on the partial pressure of carbon dioxide (CO2) in the air above the solution.

Common Chemicals in the News

Free radicals and ozone are some common chemicals in the news. Ozone, a toxic light-blue gas that protects us by absorbing ultraviolet (UV) light from space, has a chemical formula of O3. When UV hits it, it splits up into dioxygen (O2) and a free oxygen atom (O).

Free radicals are molecular fragments having one or more unpaired electrons. Paired electrons are more stable than unpaired electrons, so free radicals are short-lived and highly reactive. They can therefore alter the structure of organic compounds and impair health. Superoxide (O2-) is a potent free radical created in the normal process of metabolism. The hydroxyl radical (HO) is a free radical produced when hydrogen peroxide (H2O2) degrades. A negative sign is used to indicate a net negative charge.

Multiple Kinds of Chemical Formulas

When people think of chemical formulas, they think of CO2 and H2O. These are called molecular chemical formulas. They show the exact number and type of atoms in a molecule. There are two other kinds, though: empirical formulas and structural formulas.

Empirical formulas give the type of atoms present and ratio between them, but not the actual number of atoms per molecule. For example, the empirical formula of glucose is not C6H12O6 but instead CH2O. If it conveys less information, what is the point of this form? A molecule's structure may not be discernible, but the ratios of the atoms in it may be determinable empirically. So the best that can be recorded is the ratio between elements.

The molecular formula of two molecules may be the same. For example, the molecular formula for the common chemicals ethanol and dimethyl ether is C2H6O. Therefore, a structural formula to distinguish the two is desirable. (Note that each bar in the image represents an electron pair.)

Isotope Form

Other well-known substances are distinguished by their nuclear structure instead of their electron structure, e.g. uranium-238 or carbon-14. Chemical formulas have a certain form to distinguish isotopes. While the right side of a chemical element is to label charge count and atom count, the left side is reserved for proton and neutron count. The superscript on the left gives the sum of protons and neutrons, while the subscript on the left give the proton count.

References

• Chemistry; Raymond Chang; 1984

Resources

• Erik's Chemistry Page
• Argonne National Lab: Nomenclature
• Chemical Nomenclature