Name Ions

Naming ions is a fairly simple process when you understand the rules. The first thing to consider is if the ion is positively or negatively charged and if it is a monoatomic ion or a polyatomic ion. You also must consider whether the ion has more than one oxidation state (charge). Once you have answered all of these questions, you can follow a few simple steps to correctly name any ion.

Steps

Naming a Monoatomic Ion With a Single Oxidation State

1. Memorize the periodic table. In order to remember the names of ions, you will need to remember the names of the elements that form them. Commit the periodic table to memory, and you will have a much easier time naming ions.
   • It's fine to consult the periodic table if you can't remember the name for an element.
2. Remember to add the word ion. In order to distinguish an ion from an atom, you must use the word ion at the end of the name.
3. Use element names for positive ions. The simplest ions to name are positively charged monoatomic ions with single oxidation states. These simply take the same name as the element that forms them.
   • For example, the name for the element Na is sodium, so the name for Na+ is sodium ion.
   • Positively charged ions are also known as cations.
4. Add the -ide suffix for negative ions. Monoatomic ions with a negative charge and a single oxidation state are named using the stem form of the element name, with the addition of the suffix -ide.
   • For example, the name for the element O2 is oxygen, so the name for O2- is oxide ion. The name for the element F is fluorine, so the name for F- is flouride ion.
   • Negatively charged ion are also known as anions.

Naming a Monoatomic Ion With Multiple Oxidation States

1. Know which ions can have more than one oxidation state. The oxidation state of an ion simply means how many electrons it gains or loses. Most transition metals, which are grouped together in the periodic table of elements, have more than one oxidation state.
   • The oxidation state of an ion is equal to its charge, which is the number of electrons the ion has.
   • Scandium and zinc are the only two transition metals that do not have more than one oxidation state.
2. Use the roman numeral system. The most common way to indicate the oxidation state of an ion is to use roman numeral in parentheses to indicate the charge.
   • Continue to use the element name as you would for any positive ion. For example, Fe2+ is called iron (II) ion.
   • Transition metals do not carry negative charges, so you will not have to worry about adding the -ide suffix.
3. Be familiar with the old system. While the roman numeral system is more common today, you may encounter the older naming system, especially on labels. This system adds the suffix -ous to the ion with the lower positive charge, and the suffix -ic to the ion with the higher positive charge.
   • The suffixes -ous and -ic are relative, which means they do not correspond directly to numbers. For example, iron (II) ion would be called ferrous ion using the old system, and iron (III) ion would be called ferric ion, because iron (II) has a lower positive charge than iron (III). Similarly, copper (I) ion would be called cuprous ion and copper (II) ion would be called cupric ion because copper (I) has a lower positive charge than copper (II).
   • This system does not work well for ions that can have more than two possible charges, which is why the roman numeral system is preferred.

Naming a Polyatomic Ion

1. Understand what a polyatomic ion is. Polyatomic ions are simply ions that contain more than one type of element. These are distinct from ionic compounds, which are formed when positively charged ions bond with negatively charged ions.
   • As with ions, there is a system for naming ionic compounds.
2. Memorize the names of common polyatomic ions. The naming system for polyatomic ions is quite complex, so you may want to start by memorizing the ones that you will need to recall most often.
   • Common polyatomic ions include bicarbonate ion (HCO3-), hydrogen sulfate ion or bisulfate ion (HSO4-), acetate ion (CH3CO2-), perchlorate ion (ClO4-), nitrate ion (NO3-), chlorate ion (ClO3-), nitrite ion (NO2-), chlorite ion (ClO2-), permanganate ion (MnO4-), hypochlorite ion (ClO-), cyanide ion (CN-), hydroxide ion (OH-), carbonate ion (CO32-), peroxide ion (O22-), sulfate ion (SO42-), chromate ion (CrO42-), sulfite ion (SO32-), dichromate ion (Cr2O72-), thiosulfate ion (S2O32-), hydrogen phosphate ion (HPO42-), phosphate ion (PO43-), arsenate ion (AsO43-), and borate ion (BO33-)
   • The ammonium ion (NH4+), is the only positively charged polyatomic ion (or polyatomic cation).
3. Learn the pattern for negatively charged polyatomic atoms. Although complex, there is a pattern to the naming system for negatively charged polyatomic ions (or polyatomic anions). Once you understand the pattern, you will be able to name any ion.
   • Use the -ite suffix to indicate a low oxidation state. For example, the NO2- ion is the nitrite ion.
   • Use the -ate suffix to indicate a high oxidation state. For example, the NO3- ion is the nitrate ion.
   • Use the hypo- prefix to indicate the very lowest oxidation state. For example, the ClO- ion is the hypochlorite ion.
   • Use the per- prefix (as in hyper-) to indicate the very highest oxidation state. For example, the ClO4- ion is the perchlorate ion.
   • Exceptions to the pattern include hydroxide (OH-), cyanide (CN-), and peroxide (O22-) ions, which have the -ide ending because they were once thought to be monatomic ions.

Related Articles

• Find Oxidation Numbers
• Study the Elements of the Periodic Table
• Name Ionic Compounds
• Memorize Common Polyatomic Ions

Sources and Citations

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