
Formatting Chemical Formulas 
Introduction 
This section gives tips for formatting chemical formulas for effective searching in STN Easy. 
Chemical formulas 
Elements in a chemical formula and their counts are arranged in a standardized order called Hill System Order. 
Hill System Order 
Hill System Order rules are given. Element counts follow the element symbol. No count is used for element counts of 1. 
For chemical formulas containing  Then elements are arranged as follows:  Example 

Carbon 

C7H4Br2O2 
No carbon  Elements in alphabetical order  H2O4S 
Special representations 
Formulas for some chemical substances have special representations:

Salts of acids 
Follow these steps to determine the formula for salts of acids. 
Step  Do the following:  Example 


Write the chemical formula as it is known.  CH3COONa 

Remove the metal from the formula to create two fragments. 


Add H to the fragment where the metal was removed to create the formula for the neutral acid. 


Arrange elements of each fragment in Hill System Order. 


Combine the acid formula with the metal formula, separating each formula by a period. The carboncontaining formula comes first  C2H4O2.Na 
Salts of amines 
Follow these steps to determine the formula for salts of amines. 
Step  Do the following:  Example 


Write the chemical formula as it is known.  (CH3)3NHCl 

Move the H from the N to the anion to create two fragments. 


Arrange elements of each fragment in Hill System Order. 


Combine the amine formula with the acid formula, separating each formula by a period. The carboncontaining formula comes first.  C3H9N.ClH 
Homopolymers 
Homopolymers are macromolecules formed by linking together one type of monomer. Follow these steps to determine the formula for homopolymers. 
Step  Do the following:  Example 


Write the chemical formula for the monomer as it is known.  H2C=CHC6H5 

Arrange elements of the monomer in Hill System Order.  C8H8 

Enclose the monomer formula in parentheses, followed by X.  (C8H8)X 
Copolymers 
Copolymers are macromolecules formed by linking together more than one type of monomer unit. Follow these steps to determine the formula for copolymers. 
Step  Do the following:  Example 


Write the chemical formulas for each monomer as it is known. 


Arrange elements of each fragment in Hill System Order. 


Arrange formulas in order of decreasing carbon count, separating each formula by a period.  C4H6O2.C2H3Cl.C2H3F 

Enclose the copolymer formula in parentheses, followed by X.  (C4H6O2.C2H3Cl.C2H3F)X 