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
  1. Carbon
  2. Hydrogen
  3. Other elements in alphabetical order
C7H4Br2O2
 No carbon Elements in alphabetical order H2O4S

Special representations

Formulas for some chemical substances have special representations:

Chemical substance description Example
 Salts of acids Sodium acetate
 Salts of amines Trimethylammonium chloride
 Homopolymers Polystyrene
 Copolymers Vinyl acetate-vinyl chloride-vinyl fluoride copolymer


Salts of acids

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

 1
Write the chemical formula as it is known.  CH3COONa

 2
Remove the metal from the formula to create two fragments.
  • CH3COO
  • Na

 3
Add H to the fragment where the metal was removed to create the formula for the neutral acid.
  • CH3COOH
  • Na

 4
Arrange elements of each fragment in Hill System Order.
  • C2H4O2
  • Na

 5
Combine the acid formula with the metal formula, separating each formula by a period. The carbon-containing formula comes first  C2H4O2.Na

Salts of amines

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

 1
Write the chemical formula as it is known.  (CH3)3-NH-Cl

 2
Move the H from the N to the anion to create two fragments.
  • (CH3)3-N
  • HCl

 3
Arrange elements of each fragment in Hill System Order.
  • C3H9N
  • ClH

 4
Combine the amine formula with the acid formula, separating each formula by a period. The carbon-containing 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

 1
Write the chemical formula for the monomer as it is known. H2C=CH-C6H5

2
Arrange elements of the monomer in Hill System Order. C8H8

3
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

 1
Write the chemical formulas for each monomer as it is known.
  • CH3CO-O-CH=CH2
  • H2C=CH-Cl
  • H2C=CH-F

 2
Arrange elements of each fragment in Hill System Order.
  • C4H6O2
  • C2H3Cl
  • C2H3F

3
Arrange formulas in order of decreasing carbon count, separating each formula by a period.  C4H6O2.C2H3Cl.C2H3F

 4
Enclose the copolymer formula in parentheses, followed by X.  (C4H6O2.C2H3Cl.C2H3F)X


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