Nomenclature of inorganic chemistry

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Nomenclature is a set of guidelines for giving names. In the scope of inorganic chemistry, the guidelines set by the International Union of Pure and Applied Chemistry, also known as IUPAC, give way to the conventions that are commonly used the in world of chemistry. Fortunately for these rules, we would not have to remember a unique name for every single substance that we came across, like how we give name to other people.

In order to consider the name of an ionic compound, it is helpful to identify the elements within it.

Binary compounds consist of two elements. Perhaps you have heard the term binary before, which may refer to the computer logic of 1's and 0's. In this case, a binary ionic compound would consist of a cation and anion. Cation refers to ions with positive charges. Anion refers to ions with a negative charge. Generally, ionic compounds are written with cations justified to the left and anions justified to the right.

Let's take for example:

NaCl

This is Sodium chloride, also commonly known as table salt.

Na⁺

Cl^-

It has been deconstructed into individual Sodium and Chlorine ions. In order to understand the name behind Sodium chloride, we notice that it is composed of Sodium and Chlorine elements. Thus the cation in the naming scheme is held the same while the anion is drops the -ine ending and adds a -ide ending. Thus instead of Sodium chlorine, we have Sodium chloride

Now consider the presence of multiple anions.

CaI₂

First, we identify the cation and anion.

Ca⁺²

I₂^-

The compound has been deconstructed into individual Calcium and Iodine ions. We then follow the naming convention of a binary ionic compound. Drop -ine and add -ide. Thus the name becomes Calcium iodide. Notice that although the subscripts have magnitude, the charges are equalized.

Notice how when symbolizing Iodine, that the charge is not multiplied for an increasing subscript. The charge represents the charge magnitude on a single element.

In order to form chemical compounds using chemical symbols when given the name, one must again identify the elements. Let's take for example the name Calcium phosphide. Now the first element we identify would customarily be Calcium. Calcium on the period table is located in Group II and has a +2 charge. However, something different has occurred. When dropping -ide from phosphide and adding -ine yields Phosphine. This is incorrect. Phosphine is a completely different substance, and a compound for that matter symbolized with PH₃. When Phosphorous is named, it drops the -ous ending and adds the -ide ending.

Thus, when given Calcium phosphide we identify the elements symbolized as Ca and P. However, one important idea to keep in mind is that ionic compounds have charges that add up to 0. Hence, the charges in NaCl, with Na⁺ and Cl^- (+1 and -1, respectively), add to 0. We know that Ca has a +2 charge and P has a -3 charge. In order for the charges to add to 0, the Calcium charge must be multiplied by 3 and the Phosphorous charge must be multiplied by 2. A simple method for finding binary compound subscripts is to use the opposing ion's charge as the subscript.

Therefore, the symbol for Calcium phosphide is Ca₃P₂.

Compounds containing Polyatomic ions are simply compounds that have multiple atoms in one ion. Compounds containing polyatomic ions are simply compounds that have multiple atoms in one ion. They follow the same naming scheme as compounds with monatomic ions, however the -ide ending is not dropped.

Thus when given a compound such as CaSO₄, we first identify the ions. We see a Ca⁺² (Calcium ion) and a SO₄⁺² (sulphate ion), when the compound is deconstructed. Do not confuse the sulphate ion with a sulpharous ion. Thus, the name becomes Calcium Sulphate. Remember the metal is named the same in this case, with the exception of metallic metals. And since this a polyatomic ion, there is no need for an -ide ending.

Here is a list of common polyatomic ions that you may see in the future.^[1] You should commit these to memory.

Naming compounds within the Transition metals varies just by a little bit, but still remains in the same conventions as a binary ionic compound. Let us consider Al₂O₃. Following the naming conventions of binary ionic compounds above, we identify that the ions in this compound are Aluminum (+3) and Oxygen (-2). Notice, that elements in the transition series have variable charge, meaning that the charge may be +2, +3, or anything of the like depending on the metal. In this case, Aluminum carries a +3 charge, so in order for us to denote charges by nomenclature, we include the charge immediately following the naming of the cation.

Therefore, the name would be represented as Aluminum(III) oxide. A few things to note about this name:

• There is no space after the naming of the cation.
• Roman numerals are used to denote charge of the cation.
• Only the cation requires charge to represented.

This is because with binary ionic compounds, we are able to infer the charge of a respective anion. Let us go back to our previous examples. Sodium chloride (NaCl) can be easily inferred. We know that Sodium carries a +1 charge and Chlorine with a -1 charge. When only given the name of the compound rather than the symbol, we also already know the charges and are easily able to construct a symbolic representation of it. When considering elements with variable charge, we cannot infer with the same accuracy and require additional information. But we only need to know the cation's charge from the naming scheme, because we then know to use the simplest whole number form of a compound by allowing the charges of a compound to equal 0.

• Flowers, Paul, Klaus Theopold, Richard Langley, William R. Robinson, Mark Blaser, Simon Bott, Donald Carpenetti, Andrew Eklund, Emad El-Giar, Don Frantz, Paul Hooker, George Kaminski, Jennifer Look, Carol Martinez, Troy Milliken, Vicki Moravec, Jason D. Powell, Thomas Sorensen, and Allison Soult. Chemistry. N.p.: n.p., 2015. Chemistry. OpenStax College, Mar. 2015. Web.

Official Website for the IUPAC