Unit 15: Ionic Nomenclature

 

Unit Overview:

In the previous 2 units, you built on your understanding of both the electronic structure and the periodic table to explore the role of the electron in chemical bonding.  Ionic bonding is the result of a transfer of electrons; covalent bonding is the result of a sharing of electrons.

 

In the next 2 units, you will explore the writing of formulas and the naming of compounds that result from these ionic and covalent bonds.

 

 

What is Chemical Nomenclature?

Our world is made up of millions of substances - substances that occur naturally and substances that are synthesized by us.  How do we keep track of all of these substances?   Chemical nomenclature refers to the systematic naming of and writing the formulas of  chemical substances.  It needs to be systematic, so that scientists can be sure to accurately describe the substances that they are using in reactions, regardless of language.  Chemical nomenclature, which builds from the universal symbols of elements on the periodic table,   becomes a universal language for chemists. Different sets of rules are used to govern the naming and writing formulas for different types of substances.  These rules are developed by the International Union of Pure and Applied Chemists and is often referred to as the IUPAC System of Nomenclature.  There are rules that govern the writing of ionic compounds and a different set of rules for the writing of covalent molecules.

 

What makes up an ionic compound?

Remember that an ionic compound is a substance that is held together by an ionic bond, which refers to the transfer of electrons between atoms. When the atom transfers electrons, an ion is formed.  An ion is a charged atom or group of atoms. It is important to remember that:

1.   Ions can either be positively or negatively charged, depending on whether or not electrons have been gained or lost:

a.   A cation is s positively-charged ion because it has lost electrons. Metals form cations.

b.   An anion is a negatively-charged ion because it has gained electrons. Nonmetals form anions.

2.   Ions can be formed by single atoms or by groups of atoms.

a.   A monatomic ion is formed by a single atom gaining or losing electrons.

b.   A polyatomic ion is formed when a group of atoms has gained or lost electrons.

 

How do you know the charge of ions?

The charge of the ion, also sometimes referred to as the oxidation number, indicates how many electrons have been lost or gained by the atom or group of atoms in order for it to achieve greater stability.  When electrons have been lost, the overall charge is positive; when electrons have been gained, the overall charge is negative.

 

For monatomic ions, the charge of the ion can generally be determined by its location on the periodic table:

●     Group 1 elements (alkali metals and Hydrogen) have a +1 charge

●     Group 2 elements (alkaline earth metals) have a +2 charge.

●     Group 13 metals have a +3 charge

●     Group 15 nonmetals have a -3 charge

●     Group 16 elements have a -2 charge

●     Group 17 elements (halogens) have a -1 charge

●     Group 18 elements (noble gases) are stable and do not enter into ionic bonds

●     Groups 3 - 12 elements (transition elements) can have multiple oxidation numbers

○     There are several exceptions:

■     Silver, Ag, has an oxidation number of +1

■     Cadmium, Cd, has an oxidation number of +2

■     Zinc, Zn, has an oxidation number of +2

■     Tin, Sn, and Lead, Pb, both have multiple oxidation numbers but are not transition elements

The Periodic Table chart below summarizes the charges of monatomic ions:

 

The following chart also summarized the names and charges of common monatomic ions:

 

 

There are two essential things to notice about these monatomic ions:

1.   For elements that can have more than one oxidation number, their charge is included in the name as a Roman numeral.

2.   For anions, the name of the ion is not the same as the element name; instead, they end in -ide.

 

 

For polyatomic ions, the periodic table cannot be directly used to know the names and charges.  Instead, names and charges can be looked up.

 

The following chart summarizes the names and charges of common polyatomic ions:

 

 

There are two critical things to notice about these polyatomic ions:

1.   The most common polyatomic ions are anions.

Exception: ammonium, NH4+1; mercury (I), Hg2+2

2.   The names of most common polyatomic ions end with -ate or or -ite.

Exceptions: cyanide, CN-1; hydroxide, OH-1; peroxide, O2-2; ferrocyanide, Fe(CN)6-3

 

How is an ionic formula written?

The writing of ionic formulas is governed by the principle of electric neutrality, which describes that a compound is formed so that it has no overall charge.  Therefore, the total amount of positive charge must equal the total amount of negative charge. So, in order to write formulas correctly, it is essential to know the charges of the ions that make it up.

 

Let’s Try Some!     Write the formula for each of the following ionic compounds:

 

 

         

 

 

 

Watch the following video for a verbal and visual description of writing formulas of ionic compounds.  Writing Ionic Formulas

 

Practice 1:  Complete this online practice quiz of writing the formulas of ionic compounds from their names.

 

 

Let’s Try Some!   Write the name of each of the following ionic compounds

 

 

 

 

 

Watch the following video for a verbal and visual description of naming ionic compounds from their formulas:  Naming Ionic Compounds

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Practice 2:  Complete this online practice quiz of naming and writing ionic formulas.

 

 

ChemLab: Mystery Powder Analysis

Overview:

In this lab, you will not directly explore ionic nomenclature.  Instead, you will use scientific methods to identify an unknown substance. You will perform multiple experiments using several common powders (that include ionic compounds). The results of the research on the known powders will be used to analyze and identify several unknowns. The unknowns can be a single powder or a combination of the known powders.

 

Directions:

1.   Download the Student Exploration and Vocabulary sheets for the Mystery Powder Analysis.

2.   Familiarize yourself with the words on the vocabulary sheet.

3.   Log-in to your Explore Learning account.

4.   Click on “Mystery Powder Analysis” and launch the gizmo.

5.   Answer the Prior Knowledge Question.

6.   Practice using the Gizmo, using the Gizmo warm-up instructions.

7.   After you are comfortable using the Gizmo, begin the activity. Use the lab sheet as a guide to complete the 2 activities:

a.   Activity A: Known Substances

b.   Activity B: Unknown Substances