Naming Ionic Compounds (Nomenclature)

Transcript for Formula Units

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Naming Ionic Compounds using KembloX

In this segment, we’ll discuss the naming of ionic compounds using the KembloX™ system, which is a system comprising a color-coded chart of common ions (monatomic and polyatomic) and a set of color-coded complementary blocks, used for building models of ionic compounds, as discussed in a different segment.

Naming ionic compounds can be sometimes confusing, because of the long history of chemistry. Along this history, naming rules changed and, in the times of alchemy, were sometimes intentionally garbled. Not only the rules, but the very language of chemistry changed along history; after Latin was abandoned as the universal language of science in general, and of chemistry in particular, a true Babel of rules and words was created. In 1919, the International Union of Pure and Applied Chemistry (IUPAC) has been founded, and most chemists today obey its guidelines.

In general, the names of Ionic Compounds will be formed as

CATION NAME (always cation first) followed by ANION STEM and a SUFFIX which make one word

For example Sodium Chlor (the STEM) ide(Suffix). Together they make sodium Chloride

Using KembloX™ we’ll have a sodium ion (blue block with well) and chloride ion (blue block with little pyramid). They come together by electrostatic forces and make SODIUM CHLORIDE.

Let’s talk about the cations.

Many elements have only one preferred charge. In this case, their cation name is usually the name of the element (or polyatomic ion). Their ionic compounds are called Type I ionic compounds. The names of the corresponding ionic compounds will be straightforward:

e.g. Calcium followed by the anion name (we’ll tackle anion names a little later)

If we look at the KembloX chart, however, we notice that some elements may result in two different cations with different charge (more than one color associated with them in the chart).

The ionic compounds of these elements are called Type II ionic compounds. In this case one must have, in the name, a way to show the actual charge of the ion. In modern chemistry this way is called the Stock notation. It must be used when naming ionic compounds in which the cation can have multiple charges. In the Stock notation, the charge of the ion is indicated as a Roman numeral in parentheses, following the element name. Thus Iron(III) is Fe3+, while Iron(II) is Fe2+. Iron(III) Sulfide is a different compound than Iron(II) Sulfide.

KembloX™ is very useful in this respect, because very different blocks will represent the two different ions:

Fe(II) , a block with two wells,

will be very different from Fe(III) , a block with three wells, and we’ll give some examples of both type one and type II ionic compounds after we had discussed the anions.

Let us turn our attention to the anions

In addition to the Type I and Type II classification by the type of cation presented above, one can classify the ionic compounds into “binary”, in which only two kinds of atoms occur, and “polyatomic”, in which the number of atom kinds is larger than two. In binary ionic compounds, we encounter not two atoms, but two TYPES of atoms. For example, the ionic compound formed by sodium and chlorine, NaCl, named “sodium chloride”, is a binary compound that contains two ions: Sodium is the cation (as can be also ascertained from the KembloX™ chart), and Chloride is the anion (notice the –ide suffix). Another example is “calcium iodide”, CaI2. In calcium iodide, the formula unit is made up from one divalent cation of calcium (as per the KembloX™ chart), and two monovalent ions of Iodide: Ca+2 and I–. We notice that CaI2 is still a binary compound, although it contains a total of three ions. Other examples of binary compounds would be sodium nitride (Na3N) – 4 ions, calcium phosphide (Ca3P2) – 5 ions.


Many ionic compounds contain polyatomic anions, i.e. more than one atom type. Their naming is a little more complicated. They are still named as a stem + suffix, but the suffix or the prefic is not always obvious. In the KembloX™ system, the names of the most common polyatomic ions are listed in the chart, and the chart can be used by students until the names of the polyatomic ions are memorized. Many experienced chemists know those names by heart, also as the general naming rules. The KembloX™ Chart is a useful aid, because the rules can be confusing at times. For example, “nitrates” (NO3–), and “nitrites” (NO2–), have the same charge, but a different number of oxygen atoms, hence different suffixes. The same is valid for “sulfates” and “sulfites”: they differ by one oxygen atom. It becomes confusing, however, when we realize that “sulfates” (SO42–) have a different number of oxygen atoms than “nitrates” (NO3–), but share the same suffix.

Here is an example of three polyatomic ions with the same suffix, but different charge, meaning that three different blocks will be necessary to represent each of them:

Nitrate, Sulfate, and Phosphate

And we can see the corresponding blocks.

Here is another example of several ions, for which both suffixes and prefixes are necessary, with the same charge, but different number of oxygen atoms, which means that the same type of block will be used to represent each of them:

Chloride, hypochlorite, chlorite, chlorate, and perchlorate

Cl–, ClO–, ClO2–, ClO3–, ClO4–

In conclusion it’s suggested to use the KembloX™, chart or another list, until memorization takes hold.

Let us look at several examples that illustrate the naming principles discussed above.

First, let’s look at some common ionic compounds: sodium chloride, calcium iodide, iron(II) sulfate, iron(III) sulfate, copper(I) oxide, and copper(II) oxide.

Sodium Chloride (table salt), type I compound is one of the simplest binary ionic compounds, containing one sodium ion and one chloride ion, is obviously going to be


The KembloX™ model is …

Calcium iodide, also Type I, is easy to build, using the chart, from one calcium ion (Ca+2) and TWO iodide ions; we notice that it still is a BINARY compound, although it contains a total of three ions, but only two types.

The KembloX™ model for calcium iodide is

Iron(II) sulfate will contain, according to the chart, one iron +2, Fe+2 ion, and one divalent sulfate ion, SO4-2.

The KembloX™ model for FeSO4 is as such

On the other hand, the formula for Iron(III) sulfate, also Type II, will look totally different: it will contain trivalent iron ions, Fe+3 and the balancing number of sulfate ions, Fe2(SO4)3, as detailed in a different segment of the KembloX™ series.

The KembloX™ model for Fe2(SO4)3 is as such

The two compounds, iron(II) sulfate and iron(III) sulfate are vastly different in properties and that’s why specifying the charge of the cation in Type II ionic compounds is VERY important.

What needs to also be emphasized is that the Roman numerals in the name of the ionic compound are NOT related to the number of atoms in the formula unit. The oxides of copper are good examples.

For example, copper(I) oxide, whose formula is Cu2O, contains TWO copper ions, each with a charge of + ONE.

The KembloX™ model for Cu2O is

On the other hand, copper(II) oxide, whose formula is CuO, contains ONE copper ion, with a charge of + TWO.

The KembloX™ model for CuO is

In summary, there are general guidelines for naming ionic compounds, but the actual naming requires a lot of practice.

In other segments KembloX™ is used to build models of formula units, illustrate the concepts of ionic equation, net ionic equation, spectator ions, and limiting reagent.