Unit 1: Back to the Basics

Section 4: Naming Compounds

• Introduction
• Binary Ionic Compounds - Type I
• Binary Ionic Compounds - Type II
• Polyatomic Ions
• Binary Covalent Compounds
• Acids
• Conclusion

Introduction

The most important aspect of Chemistry is not finding new chemical processes or to be on the leading edge of technology, but to be able to communicate this new information to other chemists. Because of this, the scientific community came up with a set of rules to name compounds so that EVERYBODY would understand what reaction was taking place.

Binary Ionic Compounds - Type I

Binary ionic compounds means two ions, one that is positive in charge (cation) and one that is negative in charge (anion) that react to form a compound. In this case, the rules are:

1. The ion with the positive charge (cation) is always written before the ion with the negative charge (anion)
2. The first word is the name of the element of which the cation originally came. (Example: Na⁺ would be called Sodium)
3. The last word is the name of the element of which the anion originally came. (Example: Cl^- would become chlorine, but the first part of the word is used and -ide is added to the end, so the last word would be Chloride.)
4. Put the two words together and that is the name of the compound. (Example: Na⁺ and Cl^- would become Sodium Chloride.)

TRY IT YOURSELF: Examples and Practice Problems

Binary Ionic Compounds - Type II

As defined above, binary ionic compounds occur when two ions of opposite charge react with each other. The difference between type II and type I, occurs when ions that have the potential to have different charges react. Type II occurs when ions with the possibility to have two or more charges react.

When there is a possibility to have different charges, there are two ways of determining what the name will be. The oldest version, called the alternate name, was to use -ic and -ous endings on the end of the elements names to show what the charges were. -ic was used for the ion with the higher charge and -ous was used for the ion with the lower charge. This probably makes no sense, so here is an example. In the table above, Co (Cobalt) can have the charge of +2 or +3, so Cobaltic is Co⁺³ and Cobaltous is Co⁺². The problem with this system is the everyone must know all the possible ions for each element to know which one is the bigger one or the smaller one, so another method was created. This method is called the systematic name method. (I like this method better!!) Anyway in parentheses after the name of the element, a Roman numeral is written that indicates what the charge of the ion is. Using the example above with Cobalt, Co⁺³ would be written Cobalt (III) and Co⁺² would be written Cobalt (II).

So if Co⁺² were to react with O^-2 (Oxygen), it could be written as Cobaltous Oxide, or Cobalt (II) Oxide. (Remember, the last word ends in -ide.) Below are a few examples that incorporate both methods.

TRY IT YOURSELF: Examples and Practice Problems

Polyatomic Ions

Polyatomic Ions are ions that contain a number of ions. There is a list of polyatomic ions below. There is no way to learn how to write their names, except to commit them to memory. (When you commit them to memory, remember the charges, names, and formulas.)

Common Polyatomic Ions
Ion	Name	Ion	Name
NH4+	Ammonium	O2-2	Peroxide
NO2-	Nitrite	CrO4-2	Chromate
NO3-	Nitrate	Cr2O7-2	Dichromate
SO3-2	Sulfite	MnO4-	Permanganate
SO4-2	Sulfate	C2H3O2-	Acetate
HSO4-	Hydrogen Sulfate	ClO4-	Perchlorate
OH-	Hydroxide	ClO3-	Chlorate
CN-	Cyanide	ClO2-	Chlorite
PO4-3	Phosphate	ClO-	Hypochlorite
HPO4-	Hydrogen Phosphate	HCO3-	Hydrogen Carbonate
H2PO4-	Dihydrogen Phosphate	CO3-2	Carbonate

Binary Covalent Compounds

Binary covalent compounds are those that do not involve metals or ions. An example of the difference between a covalent compound is that CO₂ is a covalent compound, but NaCl is not, because it contains Na⁺, a metal and an ion.) Here are the rules for naming a binary covalent compound.

1. The first element in the formula uses the whole name of the element, much like binary ionic compounds. (Example: In NO, the first word would be Nitrogen.)
2. The second element in the formula only uses the first half of the word and -ide is added in place of the removed ending, much like binary ionic compounds. (Example: In NO, the first part of the second word would be -oxide.)
3. So the person reading the name can determine what the subscript is on each element, a prefix is added to show how many of each element are used. The first word of the formula does not use momo, so CO (Carbon Monoxide), NOT (Monocarbon Monoxide).

TRY IT YOURSELF: Examples and Practice Problems

Acids

Acids will be discussed in depth later in this On-Line Text Book, but for now, acids are defined as any substance with a H⁺ in it. For example, H⁺ and Cl^- form HCl, which is an acid. Naming acids depends on whether or not there is oxygen in the acid. If there is no oxygen, take away the first word, which is hydrogen, and add hydro- to the beginning of the last word and and add -ic or sometimes -ric to the last word. For example, HCl, in the binary ionic compound format would be Hydrogen Chloride, but as an acid it is Hydrochloric Acid.

If there is oxygen in the anion, then there is another set of rules. This set of rules involves adding -ic or -ous to the end of the second word, and taking away the first word, which is hydrogen. If the anion ends in -ate then -ate is replaced by -ic. If the anion ends in -ite, then the -ite is replaced by -ous. An example is HNO₂ and HNO₃. HNO₂ is called hydrogen nitrite by the binary ionic compound rules, and when it is named as an acid the name is nitrous acid. HNO₃ is called hydrogen nitrate by the binary ionic compound rules, and when it is named as an acid it is called nitric acid.

TRY IT YOURSELF: Examples and Practice Problems

Conclusion

This particular section contains a lot of important information, and this information is used over and over and over again. It is very important to know these rules inside and out. It is also important to know how to write the chemical name from the chemical formula and vice versa.