Naming Compounds
Naming compounds is an important part of chemistry. Most compounds fall in to one of three categories- ionic compounds, molecular compounds, or acids.
Part One: Naming Ionic Compounds
Identifying Ionic Compounds
Ionic compounds consist of combinations of positively charged ions called cations (usually metals), and negatively charged ions called anions (usually non-metals). In general, you can identify an ionic compound because it contains a metal (these are usually found in the left and center areas of the periodic table) and a non-metal (these are generally found in the right hand area of the periodic table). Also, a compound will have no charge. For example, NaCl and Fe2O3 are ionic compounds; they each contain a metal (Na and Fe) and a non-metal (Cl and O), and they do not have charges. MnO4- is NOT an ionic compound; it does contain a metal (Mn) and a non-metal (O), but it has a charge. Thus, it is a polyatomic ion, not a compound. A compound will NEVER have a charge!
Naming Ionic Compounds
There are three steps involved in naming ionic compounds- naming the cation, naming the anion, and naming the entire compound.
1. Name the cation.
i. Cations formed from metal atoms have the same name as the metal.
Examples: Na+= sodium ion; Al3+= aluminum ion ii. If a metal can form ions of different charges (i.e., is one of the central transition metals), specify the charge with Roman numerals in parentheses. Examples: Fe+= iron (I) ion; Fe2+= iron (II) ion; Fe3+= iron (III) ion iii. Cations formed from nonmetal ions have names ending in –ium.
These are not common; the main ones are NH4+ (ammonium ion) and H3O+ (hydronium ion)
2. Name the anion.
i. Monoatomic anions (those formed from a single atom) have names formed by replacing the end of the element name with –ide.
Examples: F- = fluoride ion; O2-= oxide ion. A few simple polyatomic anions (those formed from multiples atoms) also have names ending in –ide. Examples: CN- = cyanide ion; OH- = hydroxide ion; O22-= peroxide ion. ii. Most polyatomic ions contain oxygen, and have names ending in ate or -ite. They are known as oxyanions. The ending –ate is used for the most common oxyanion form. The ending –ite is used for an

Provided by Tutoring Services

1

Naming Compounds

oxyanion that has the same charge, but one less oxygen atom.
Examples: SO42- = sulfate; SO32- = sulfite (same charge, but one less oxygen). iii. The suffixes per- and hypo- are added to the names of oxyanions to show the addition or subtraction of additional oxygen atoms. Perindicates the addition of one oxygen to the -ate form. Hypo- indicates the subtraction of one oxygen from the –ite form. Thus –ate is the most common form, per-_-ate has one extra oxygen, -ite has one less oxygen, and hypo-_-ite has two less oxygen. Example:
ClO4- = perchlorate (one more oxygen than regular form)
ClO3- = chlorate (regular form)
ClO2- = chlorite (one less oxygen than regular form)
ClO- = hypochlorite (two less oxygen than regular form) iv. Anions formed by adding H+ to an oxyanion have the word
“hydrogen” in front of their names (or “dihydrogen,” if two hydrogens are present.) Examples: CO32- = carbonate ion; HCO3- = hydrogen carbonate ion (notice that the addition of hydrogen lessens the negative charge by one). PO43- = phosphate ion; H2PO4- = dihydrogen phosphate.
3. Name the compound.
i. To name the compound, simply put the names of the ions together.
The name of an ionic compound is always the cation name followed by the anion name. Examples: CaCl2= calcium chloride; Al(NO3)3= aluminum nitrate ii. If you are dealing with a transition metal, don’t forget to specify its charge. iii. If you are dealing with an oxyanion, be sure you have the right name for the form you are using. Example: Cu(ClO4)2 = copper (II) perchlorate iv. If you are having trouble determining the charge on an ion, look at the subscript on the opposite ion. In the