Naming Ionic Compounds

Core Concepts

In this tutorial, you will learn about nomenclature and naming ionic compounds. We will derive names from the chemical formulas of binary and polyatomic ionic compounds.

Topics Covered In Other Articles

• IUPAC Naming of Organic Compounds
• Naming covalent compounds   
• Molecule vs compound
• Naming alkanes
• Common Polyatomic Ions

Vocabulary 

• Compound: substance containing molecules that consist of atoms from two or more chemical elements (can be ionic or covalent)
• Ion: atom or group of atoms that possess an electric charge
• Charge: found by subtracting (protons-electrons); changes during ionic bonding due to electron transfer
  • Cation: positively charged ion; formed when neutral atom loses electrons
  • Anion: negatively charged ion; formed when neutral atom gains electrons 
• Ionic bond: compounds formed by the transfer of electrons between cations and anions
  • Cation participant is almost always a metal 
  • Anion participant is almost always a non-metal 
• Binary Ionic Compound: has two constituents, each of which is comprised of atoms from a single element
  • Monatomic: atoms of only one element  
• Polyatomic Ionic Compound: each constituent contains atoms from more than one element
  • Can stand alone as polyatomic cation and anion
    • Acts as a single, charged unit
  • Can combine to form compounds 

Introduction to Naming Compounds

What are ionic compounds? Ionic compounds form when atoms or molecules attract others with opposite charges. This interaction typically occurs between a metal, which carries positive charge, and a nonmetal, which carries negative charge. The electrostatic attraction between the participants facilitates electron transfer between them. 

These compounds arrange themselves into a “lattice” structure. The ionic lattice ensures that each ion forms regular patterns with the oppositely charged ions surrounding it. To name these compounds, you must consider their ion constituents.

Naming Binary Ionic Compounds 

First, we will learn how to name binary ionic compounds. The two participants may be monatomic. Or they may be composed of multiple atoms, respectively. Either way, the binary ionic naming process will apply. 

Compounds of metals with halides or oxygen are usually ionic solids, which have a lattice connecting the cations and anions, held together with electrostatic forces.

Steps to Naming Ionic Compounds

Here are general steps to naming compounds, let’s look at the steps and then discuss some of them in details.

1. Identify the elements present in the compound. The first step in naming a chemical compound is to identify all of the elements that are present in the compound. This may involve using a chemical formula to determine the elements and their ratios, or it may involve observing the physical and chemical properties of the compound to determine its composition.
2. Determine the ratio of the elements in the compound. Once you have identified the elements in the compound, the next step is to determine the ratio of those elements. This is important because many chemical compounds have multiple possible names depending on the ratio of their elements. For example, a compound with one carbon atom and one oxygen atom could be called either carbon monoxide or carbon dioxide, depending on the ratio of the elements.
3. Use the element names and the ratio to determine the compound’s name. Once you know the elements present in the compound and the ratio of those elements, you can use the naming conventions for chemical compounds to determine the compound’s name. In general, the name of a compound will consist of the names of the elements it contains, along with prefixes and suffixes that indicate the ratio of the elements. For example, if a compound contains one carbon atom and two oxygen atoms, it would be named “carbon dioxide” because the prefix “di-” indicates that there are two oxygen atoms present.

Ok, let’s look at some of the details in naming compounds:

Name the Cation First

The cation, or the positively charged particle, always begins the compound’s name. However, the specific naming conventions will vary between elemental groups. 

Groups One and Two

Elements found within the first and second groups on the periodic table always form ions with a charge equal to their group number. This steady trend means that compounds containing one of these elements will begin simply with its name. 

For instance, the potassium ion from group one always carries a charge of 1+. The name of its compound would thus begin with “potassium.” The same goes for group two. To name a compound containing a magnesium cation, which has a 2+ charge, you would start by writing “magnesium.”  

A few metals outside of these two groups also almost always carry the same charge. Aluminum, zinc, scandium, and silver will usually have a charge of +3, +2, +3, and +1 respectively and therefore no not use roman numerals like other metals do.

Naming the Anion Second

After writing the name of the cation, you can place the name of the monatomic anion followed by the suffix “ide.” For example, the chemical formula KCl produces the name “potassium chloride.”

Naming Transition Metal Cations

But things get a bit more challenging once you expand beyond groups one and two. Recall that compounds desire a neutral, or zero, net charge. The cation’s positive charge must balance the anion’s negative charge. 

Elements in groups three-twelve, called the transition metals, lose different numbers of electrons depending on the situation. They form cations with different charges, generating unique compounds with dissimilar properties. You determine the charge of a transition metal cation by equating it to the opposite value of its given anion constituent, taking all atoms into account.

The Stock System

To address these variations, use the Stock System. This method employs roman numerals to indicate the cation’s charge in a compound. You must place the numerals in parenthesis and follow that with the word “ion.”

Fe²⁺ and Fe³⁺ are key examples; iron can carry either a 2+ charge or a 3+ charge. If the anion carries a 3- charge, choose a 3+ charge for the cation. If the anion carries a 2- charge, choose a 2+ charge for the cation. You can clarify which is the case by calling the cation either “iron(II)” or “iron(III).” 

To reiterate, elements that form ions with only one charge need not be written this way. The method eliminates ambiguity specifically around transition metal charges.

The process for writing the anion in this case remains unchanged. You place name of the anion element after the transition element cation and its charge. For instance, the compound Co₂Cl would translate to the name “cobalt(II) chloride.” 

Examples of Binary Ionic Compounds: 

• NaCl: sodium chloride
• ZnI₂: zinc iodide
• Al₂O₃: aluminum oxide 
• FeCl₃: iron (III) chloride
• PbO: lead (II) oxide

For more help, please enjoy our animated lecture on naming ionic compounds!

Polyatomic Ionic Compounds 

Polyatomic compounds contain more than one type of atom.

They might have one monoatomic component and one polyatomic component, as exemplified by NaNO₃, sodium nitrate. Or they could have two polyatomic components, as seen in (NH₄)₂SO₄, ammonium sulfate. 

Polyatomic ionic compounds may initially seem complex. Because they themselves are compounds, their titles include conventionalized names. But their naming process also involves writing the cation first, followed by the anion.

For instance, NaNO₃ is called “sodium nitrate.” Sodium is named in accordance with the same rules above. But NO₃ , being its own compound, must be referred to as “nitrate.” (NH₄)₂SO₄ contains two polyatomic ions, ammonium and sulfate. Combining the cation and the anion component gives “ammonium sulfate.”

Examples of Polyatomic Ionic Compounds: 

• CaCO₃: calcium carbonate 
• NH₄NO₃: ammonium nitrate 
• KNO₃: potassium nitrate
• Fe(OH)₂: iron (II) hydroxide 
• Na₃PO₄: sodium phosphate 
• Sn₃(PO₄)₄: tin (IV) phosphate 

You should be familiar with common polyatomic cations and anions, so that you can use them while naming ionic compounds. The chart below provides a summary of the cations and anions to be aware of. 

Common Polyatomic Ions:

Simplified Steps to Naming Ionic Compounds 

To review this information on naming ionic compounds, consult the following flowchart. It includes the steps of the naming process in different scenarios. You can also try an ionic compound worksheet.

Properties of Ionic Compounds

Ionic compounds share a lot of similar properties. Let’s look at what they are:

• They are crystalline solids
• They are hard and brittle, often breaking along smooth planes when shattered
• They have high melting and boiling points, because of their strong crystal lattices
• If they are soluble in water, they are often insoluble in nonpolar solvents
• They have high enthalpies of vaporization and fusion
• As solids, they are insulating and do not conduct electricity, but they do conduct when molten, or when dissolved in water

Practice Problems

Section I. Name the following ionic compounds:

Section II. Provide the chemical formula for the following ionic compounds:

1. Mercury(I) Chloride
2. Sodium Permanganate
3. Lead(II) Oxide

Practice Problem Solutions

Section I.

1. Copper(II) Chloride
2. Zinc Hydroxide
3. Silver Nitrate

Section II.