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The Rule for Naming Ionic Compounds

Ionic Compounds are made up from metals and nonmetals. When you intend to label them in terms of names you need to follow a simple rule for naming ionic compounds.

Naming Ionic Compounds is putting the names of metals first and then writing the names of nonmetals. For example, if you want to name the compound that forms with the result of a reaction of lithium and sulfur, you need to write the name of metal at the first place i.e. lithium, and then the name of nonmetal by adding –ide- at the end. With this sulfur becomes sulfide – Li2S (Lithium sulfide)

Naming Ionic Compounds – Polyatomic Ions.

Ionic compounds that contain polyatomic ions follow the same fundamental rule that has been explained in the above lines. That rule states that put the name of the metal at the first place and then adding the name of the nonmetal, simply, with the polyatomic anions. The ending –ide- will be replaced with –ate- in this case. For example, (NH4)2CO3 will be named as Ammonium Carbonate, K3PO4 will be named as potassium Phosphate and so on..

Naming Ionic Compounds – Roman numerals

If the involved metal is a transition metal that has more than one oxidation state, these compounds can be correctly named in more than one way.

For example, let us suppose that you want to name the compound that is formed in the result of a reaction between cations Fe+3 and CN- which is cyanide ion. The standard or preferred method is to write the name of the metal followed by the ionic charge in parentheses. Note that the ionic charge should be written in Roman numerals, like Iron(III).

There is a traditional method also available for naming ionic compounds, which is still in use, that is, to use –ous and –ic in the end. The ion that has the lower oxidation state or lower numeral charge (ignore the + or -) should be given with an ending of –ous. Whereas the ion that has higher oxidation state (with higher numeral charge) is given an –ic ending.

Hence the iron and cyanide compound can be named as Fe(CN)3 or Iron(III) cyanide or ferric cyanide.

At times, you will feel that figuring out charge on an ion is a bit challenging, and fun as well. For example, let us suppose that you took the task to name the following ionic compound:


In this compound, sulfate ion has a -2 charge and from the above formula, you can observe that there are two present. It means that you have a total of four negative charges on sulfate. On the other hand, ammonium has a +1 charge, so you can determine the charge on the iron as cation.

Since you have a -4 charge for the sulfates and a +1 for ammonium, the iron must be a +3 to make the resulting compound a neutral one. Hence, the iron is in a higher oxidation state, that is iron(III) or ferric. So you can name the compound as:

Iron(III) ammonium sulfate or ferric ammonium sulfate or FeNH4(SO4)2.


Simultaneously, you can derive the formula and charge on the ions if you have the name of the compound. For example, let us suppose naming ionic compounds in the case that you have the name cuprous oxide and you know that cuprous ion is Cu+ and the oxide ion is O2-

By applying traversed rule, we get the formula as Cuprous oxide Cu2O.

Naming ionic compounds – a further brief

The chemicals most students encounter during chemistry course(s) certainly fall into a number of categories. These are acid, binary, coordination, ionic, molecular and organic compounds. Each of these categories of compounds uses a unique “naming ionic compounds” system. You will be asked to name and write formulas for acids and binary molecular compounds, common ionic compounds and simple organic compounds in your chemistry class.

As you already came to know that each of these classes of compounds uses a unique system for naming ionic compounds, the foremost step to correctly name them is to identify the type of that particular compound. You can step forward in naming ionic compounds by looking at the formula.


Naming Ionic Compounds – a rule of thumb to follow

    • Ionic Compounds: Remember as a simple rule of thumb; ionic compounds usually consist of a metal and one, or more than one, non-metals. The main exceptions to this are those ionic compounds that enclose the ammonium ion (NH4+). Also, remember that all those compounds whose formulas begin with NH4+ are also accepted as ionic compounds.
    • Binary Molecular Compounds: Remember as a general rule that binary molecular compounds comprise of two different non-metals.
    • Acids: Inorganic acids that do not contain a C-C skeleton will start with "H" (or H2 or H, etc)
    • .


This means that to name an ionic compound one simply required to find the names of the positively charged cation and negatively charged anion present in that compound.

Naming Ionic Compounds: How to Identify the cation

As we have already discussed the cation is always written in the first place in the formula for any ionic compound.

Cations are mostly monoatomic; they consist of only one atom that has lost its electrons to become positively charged, metal ions. In such types of compounds, the cation will be the first element that needs to be written.

Numerous, but not all, evolutionary metals including tin(Sn), bismuth(Bi), and lead(Pb) can outline more than one cations. You can use Roman numerals in parentheses following the name of that element to signify the charge on such ions.

The single common polyatomic ion that you will encounter in your chemistry course is the ammonium ion which is denoted as: (NH4+).

How to Identify the anion in Naming Ionic Compounds

Hide the cation and what will be leftover will be the anion.

Put down the name of the ionic compound by writing down the name of the cation, the name of the anion will follow the name of the cation.

Make use of the list of names of ions from your course book, from your chemistry syllabus or from the hand-out that your teacher has provided. Remember that chemistry students are supposed to know the names and formulas of ions listed in their syllabus and the names of the ions as well.

Things to remember- atoms, cations and anions

Atoms are neutral basically and electrically because the number of protons and electrons is equal in the atom. Protons carry 1+ charge and electrons carry1- charge so they cancel out each other and making the net charge of an atom as zero. However, most atoms can gain or lose electrons and whenever they do so the number of electrons differs from the number of protons present in the nucleus. The result is a formation of charged species known as ‘ion’.p>

When an atom that possesses a zero or neutral charge loses one or more electrons the total number of electrons decreases in the nucleus. On the other hand, the number of protons remains the same. This activity makes an atom cation – an ion that has a net positive charge.

An opposite process can also happen, for example, when a zero charged or neutral atom gains one or more electrons, the total number of electrons in the nucleus increases while the total number of protons remains the same. This makes an atom an anion with a net negative charge.

Understand this basic activity and you will find your exercise of naming ionic compounds an easy task.

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