Lesson 2.5 Chemical Nomenclature
Suggested Readings:

Zumdahl Chapter 2 Section 2.8
Essential Question: Why is it important to have a system
for naming chemical compounds?
Learning Objectives:



State the names of compounds using oxidation numbers.
Name and write the formula of ionic compounds, molecular compounds
and acids.
Become familiar with common simple acids, oxyacids and
oxyanions.
Before the structural basis of chemical substances became established,
compounds were named after people, places or particular characteristics.
Examples are Glauber's salt (sodium sulfate, discovered by J.R. Glauber),
sal ammoniac (ammonium chloride, named after the ancient Egyptian
deity Ammon from the temple near which the substance was made) and
washing soda (sodium carbonate, used for the softening of wash water.
Today several million compounds are known and thousands of new ones
are discovered every year. Without a system for naming compounds,
coping with this multitude of substances would be a hopeless task.
Chemical nomenclature is the systematic naming of chemical compounds.
Chemical compounds are classified as either organic or inorganic. Organic
compounds are compounds that contain carbon combined with other
elements such as hydrogen, oxygen and nitrogen. Inorganic compounds are
compounds composed of elements other than carbon. However, a few simple
compounds of carbon, including carbon monoxide, carbon dioxide,
carbonates and cyanides are generally considered to be inorganic.
In this lesson we will discuss the nomenclature of some simple inorganic
compounds. We will look at both ionic and molecular compounds, acids and
hydrates. The naming of organic compounds will be discussed later in this
course.
Your study guide contains a lot of helpful information about this topic. Please
study it carefully. You must be able to both apply the naming rules to a
variety of compounds and to derive chemical formulas from names. There will
be many problems throughout this course and on the AP & IB exams where
these skills will be required.
Naming Monatomic Ions:
Watch the following video on naming ions.
Rules for Naming Ionic Compounds:
1. The cation is always named first and the anion second.
2. The cation takes its name from the name of the element. For
example, Na+ is called sodium in the names of compounds
containing this element.
3. Use a roman numeral to indicate the charge on a cation when the
cation forms more than one ion. For example, the compound FeCl₂
contains Fe2+ ions and and is called Iron(II)chloride (pronounced
iron "two" chloride).The use of roman numerals in this way is
sometimes called the stock system.
4. The anion is named by taking the root of the element and adding ide. For example, Cl- is called chloride.
Ionic Compounds Containing
Polyatomic Ions:
Recall that a polyatomic ion is an ion consisting of two or more atoms
chemically bonded together and carrying a net electric charge. Polyatomic
ions are assigned special names that must be memorized to name the
compounds containing them.
Oxyanions:
Many polyatomic anions are also oxyanions (aka oxoanions) because they
contain oxygen with another element called the characteristic or central
element. These anions are grouped by the characteristic element and are
distinguished from one another with prefixes and/or suffixes. Here's is how
they are named:
1.
2.
3.
4.
Oxyanions have a stem name from the characteristic element.
The suffix -ate is given to the oxoanion with the greater number of
oxygen atoms.
The suffix -ite is given to the oxyanions with the lesser number of
oxygen atoms (See the table below).
When there are more than two oxyanions, the prefixes hypo- and perare used in addition to the suffixes. The two oxyanions with the least
number of oxygen atoms are named using the suffix -ite and the prefix
hypo- is added to the one of these two ions with the fewer oxygen
atoms. The two oxyanions with the greatest number of oxygen atoms
are named using the suffix -ate and the prefix per- is added to the one
of these two ions with greater number of oxygen atoms (see the
oxyanions of chlorine for an example).
The Prefix ThioThe prefix thio- means that that an oxygen atom in the root ion name has
been replaced by a sulfur atom.
Sulfate and Thiosulfate Ion
Watch the video on naming ionic compounds. Then, watch the video on on
writing formulas from the names of ionic compounds.
Hydrates:
A hydrate is a compound that contains water molecules weakly bound in its
crystals. Watch the following video on hydrates to learn how to name
and write formulas for these types of compounds.
Rules for Naming Molecular
Compounds:
Binary compounds containing two nonmetals or two metalloids are usually
molecular compounds and are named using a prefix system. The rules for
naming are very similar to the rules for ionic compounds.
1.
2.
3.
4.
The first element in the formula is named first, using the full element
name.
The second element is named as if it were the anion.
Prefixes are used to denote the numbers of atoms present.
The prefix mono- is never used for naming the first element. For
example, CO is carbon monoxide, not monocarbon monoxide (See
table below, but remember the prefix mono- is used with the second
element).
Watch the video about names and formulas for molecular compounds.
Now try some more practice problems!
Acids:
Acids are an important class of compounds, and we will look closely at them
later in this course. Here we want merely to see how we name these
compounds and how they are related to the anions we encounter in some
ionic compounds. For our present purposes, an acid is a molecular compound
that yields hydrogen ion, H+, and an anion for each acid molecule when the
acid dissolves in water. For example, when nitric acid, HNO₃, is dissolved in
water it yields one H+ ion and one nitrate ion, NO₃-.
In general, the rules for naming acids depends on whether the anion
contains oxygen.
If the anion does not contain oxygen the acid is named with the prefix
hydro- and the suffix -ic. For example, when HCl(g) is dissolved in water is
forms hydrochloric acid.
Oxyacids are oxyanions bonded to one or more hydrogen ions (H+). These
are essentially polyatomic ions to which hydrogen has been bonded. When
the anion contains oxygen, the acidic name is formed from the root name of
the anion with a suffix of -ic or -ous, depending on the name of the anion.
1. If the anion name ends in -ate, the suffic -ic is added to the root
name. For example, H₂SO₄ contains the sulfate ion and is called
sulfuric acid.
2. If the anion name ends in -ite, the -ite is replaced by -ous. For
example, H₂SO₃ contains the sulfite ion and is called sulfurous
acid.
Prefixes may be used to denote the number of hydrogen atoms for some
oxyacids. For example, monohydrogen phosphate ion is essentially a
phosphate ion to which one hydrogen ion has bonded. Similarly, dihydrogen
phosphate ion is a phosphate ion to which two hydrogen ions have bonded.
Types of Phosphate Ions