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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 |
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Carbon |
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C7H4Br2O2 |
No carbon | Elements in alphabetical order | H2O4S |
Special representations |
Formulas for some chemical substances have special representations:
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Salts of acids |
Follow these steps to determine the formula for salts of acids. |
Step | Do the following: | Example |
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Write the chemical formula as it is known. | CH3COONa |
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Remove the metal from the formula to create two fragments. |
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Add H to the fragment where the metal was removed to create the formula for the neutral acid. |
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Arrange elements of each fragment in Hill System Order. |
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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 |
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Write the chemical formula as it is known. | (CH3)3-NH-Cl |
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Move the H from the N to the anion to create two fragments. |
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Arrange elements of each fragment in Hill System Order. |
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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 |
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Write the chemical formula for the monomer as it is known. | H2C=CH-C6H5 |
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Arrange elements of the monomer in Hill System Order. | C8H8 |
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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 |
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Write the chemical formulas for each monomer as it is known. |
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Arrange elements of each fragment in Hill System Order. |
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Arrange formulas in order of decreasing carbon count, separating each formula by a period. | C4H6O2.C2H3Cl.C2H3F |
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Enclose the copolymer formula in parentheses, followed by X. | (C4H6O2.C2H3Cl.C2H3F)X |