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3.1: Background - Naming Ionic Compounds

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    Ionic compounds contain cation and anions. At the simplest level, to name an ionic compound is simply to name its cation and to name its anion, in that order. Cations have a positive charge. Anions have negative charge. The charges of ionic compounds balance to give a neural charge. We can determine the cation-to-anion ratio simply by balancing the charges to determine the structure. Typically, if a compound is a mixture of a metal and a nonmetal, we will use the naming convention for ionic compounds.

    Naming Cations

    For single atom cations in groups 1A, 2A, and 3A, the name is the same as the atomic name. The charge is the same as the group number. Examples are shown in Table 1.

    Table \(\boldsymbol{\PageIndex{1}}\) – Examples of Single Atom Cations with Consistent Charge

    Element

    Cation

    Ion Name

    Sodium

    Na+

    Sodium

    Magnesium

    Mg2+

    Magnesium

    Aluminum

    Al3+

    Aluminum

    For single atom cations that are transition metals, the charge can vary. Thus, the name of the cation also needs to include the charge. This is shown as a parathesis after the name with a Roman numeral that indicates the charge. These ions also have had common names in the past. These are listed in the table as they are still in use in some places, but you do not need to memorize them! They are there for your reference.

    Table \(\boldsymbol{\PageIndex{2}}\) – Examples of Single Atom Cations with Variable Charge

    Element

    Cation

    Ion Name

    Common Name

    Iron

    Fe2+

    Iron(II)

    Ferrous

    Iron

    Fe3+

    Iron(III)

    Ferric

    Copper

    Cu+

    Copper(I)

    Cuprous

    Copper

    Cu2+

    Copper(II)

    Cupric

    Manganese

    Mn2+

    Manganese(II)

    N/A

    Manganese

    Mn4+

    Manganese(IV)

    N/A

    Manganese

    Mn7+

    Manganese(VII)

    N/A

    A polyatomic ion contains a group of atoms that are covalently bonded together. The charge is for the overall group of atoms. We discuss one polyatomic cation, ammonium. The ammonium ion is NH4+. This is the one exception we will see to ionic compounds being a mixture of nonmetals and metals.

    Naming Anions

    We will discuss two types of anions: single atom ions and polyatomic ions. Single atom ions are typically nonmetals. The charge of these single atom ions is determined by the number of electrons an atom needs to gain to become a stable anion. For hydrogen, this is one electron. For group 5A elements, this is 3 electrons. For group 6A elements, this is 2 electrons. For group 7A elements, this is one electron. To name a single atom anion, first list the prefix and “-ide.” The prefix is determined by dropping letters from the end of the chemical name. Table 3 demonstrates how to name single atom anions.

    Table \(\boldsymbol{\PageIndex{3}}\) – Single Atom Anions

    Element

    Anion

    Ion Name

    Hydrogen

    H-

    Hydride

    Nitrogen

    N3-

    Nitride

    Phosphorus

    P3-

    Phosphide

    Oxygen

    O2-

    Oxide

    Sulfur

    S2-

    Sulfide

    Fluorine

    F-

    Fluoride

    Chlorine

    Cl-

    Chloride

    Bromine

    Br-

    Bromide

    Iodine

    I-

    Iodide

    Naming Polyatomic Ions

    Polyatomic ions are groups of atoms that are covalently bonded together and have an overall charge on the structure. The names for polyatomic ions are more variable, but a few trends exist. For oxygen containing polyatomic ions, for ions with the same central atom (non-oxygen atom), the ion with more oxygen atoms in the structure will end in “-ate” while the one with fewer will end in “-ite.” If even more oxygen atoms can be added, it will have a prefix of “per-” added to the “-ate” ion. If even fewer oxygen atoms are present than in the “-ite” ion, the prefix of “hypo-” is added. Hypochlorite (ClO-), chlorite (ClO2-), chlorate (ClO3-), and perchlorate (ClO4-), are examples of this style of naming polyatomic ions.

    Another common change to polyatomic ions is to add a hydrogen cation and the charge becomes more positive by one. This change can be indicated by adding the word “hydrogen” in front of the polyatomic ion name or by adding the prefix “bi-” to the polyatomic ion name. For example, carbonate has a formula of CO32- while bicarbonate has a formula of HCO3-. Bicarbonate is also called hydrogen carbonate.

    Be very careful with spelling! For example, nitride (N3-) is chemically very different from nitrite (NO2-), although the spelling is similar.

    Table \(\boldsymbol{\PageIndex{4}}\) – Common Polyatomic Ions

    Polyatomic Ion

    Ion Name

    NH4+

    Ammonium

    ClO-

    Hypochlorite

    ClO2-

    Chlorite

    ClO3-

    Chlorate

    ClO4-

    Perchlorate

    NO2-

    Nitrite

    NO3-

    Nitrate

    CO32-

    Carbonate

    HCO3-

    Bicarbonate (Hydrogen Carbonate)

    PO43-

    Phosphate

    OH-

    Hydroxide

    O22-

    Peroxide

    CH3COO-, C2H3O2-

    Acetate

    SO42-

    Sulfate

    CN-

    Cyanide

    This page titled 3.1: Background - Naming Ionic Compounds was last modified on Mon, 03 Nov 2025 03:24:11 GMT and is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by Georgia Fritz.