The following study guides are linked to Anne McKenna's website (http://employees.csbsju.edu/amckenna/CH123), with permission by the author.

Nomenclature

Nomenclature is the process of naming chemical compounds.  The names of these compounds are governed by rules set up by the International Union of Pure and Applied Chemistry (IUPAC).  This unit will teach you to determine the name of a compound from its formula and the formula of a substance from its name.

The Periodic Table

The periodic table is the first guide to the determination of the type of compound.  Metals are generally found on the left side of the table, nonmetals on the right, with metalloids (elements with both metallic and nonmetallic characteristics) appearing next to the dividing line between metals and nonmetal

Types of Compounds

The first step in naming a compound is to recognize the type.  Compounds are generally grouped into two types: covalent and ionic. 

Covalent compounds are composed of nonmetallic elements, bonded together with a covalent bond.  Some examples of covalent compounds are:  CO₂, H₂O and N₂O₅. 

Ionic compounds are composed of metallic cations (+ ions) and nonmetallic anions (- ions), held together by ionic bonds.  Some examples of ionic compounds are:  NaCl, MgF₂ and CaCO₃.

1.  Determine if the following compounds are ionic or covalent:

            a.  K₂O

            b.  FeS

            c.  CCl₄

            d.  SCl₂

Naming Covalent Compounds

Different covalent compounds, with different formulas, may exist between two nonmetals.  For example, two compounds can form between the nonmetallic elements carbon and oxygen.  These two compounds, CO and CO₂, must be named differently. 

Therefore, in order to name covalent compounds, you must give the number of each type of atom in the formula.  The general pattern of names is to use prefixes to indicate the number of atoms.  The first element listed is given its element name, while the second element is given the root of its element name + “ide”.

The prefixes used to indicate the number of each type of atom are listed below:

            1          mono  (not used for the first element, used infrequently for the second)

            2          di

            3          tri

            4          tetra

            5          penta

            6          hexa

            7          hepta

            8          octa

            9          nona

            10        deca

So, the two carbon-oxygen compounds above would be named

            CO      carbon monoxide

            CO₂     carbon dioxide

2.  Name the following covalent compounds:

            a.  SO₃

            b.  P₂O₅

            c.  H₂O

Charges of Ions

Some elements form ions with characteristic charges.  It is helpful to know these charges so that, if necessary, you can use these to determine charges of other ions.  For example, many groups in the periodic table have characteristic charges.  Elements in Group IA (H, Li, Na, K, Rb, Cs) have a characteristic charge of +1; elements in Group IIA (Be, Mg, Ca, Sr, Ba) have a characteristic charge of +2 and elements in Group IIIA have a characteristic charge of +3.  Elements in Group VIIA (F, Cl, Br, I) form –1 ions, elements in Group VIA (the oxygen group) form –2 ions and elements in Group VA (the nitrogen group) form –3 ions.

3.  Give characteristic charges of the following ions.

            a.  Sr

            b.  S

            c.  Al

            d.  K

Naming Ionic Compounds

Ionic compounds, composed of a metal and one or more nonmetals, may be classified into several categories.  It is much easier to name these compounds if you can classify them into categories first.

Binary Compounds

Binary compounds are composed of only two elements.  For example, NaCl and MgI₂ are both binary compounds.  These binary ionic compounds can be further classified into two types.

Binary type I compounds are composed of (usually) a main group metal with a nonmetal.  Main group metals are those in the A groups of the periodic table.  The formulas of these compounds are determined by the charges of the ions forming the compound.  For example, NaCl is a 1:1 compound because the Na ion is +1 and the Cl ion is –1.  The compound between magnesium and iodine is MgI₂ because the Mg ion is +2 and the I ion is –1.  It is not possible to have a compound between magnesium and iodine with a different formula because the ions can only have one charge. 

In naming binary type I compounds, the only name necessary is to name the cation and the anion.  Do not use the prefixes for covalent compounds to indicate the number of atoms in the formula because the number of atoms cannot vary.  So we name these compounds giving the full name of the cation (listed first) plus the anion name (root name of element + “ide”).  So, the name of the two ionic compounds above would be

            NaCl    sodium chloride

            MgI₂    magnesium iodide

3.  Name the following compounds:

            a.  CaO

            b.  K₂S

            c.  AlCl₃

Binary type II compounds are composed of a transition metal with a nonmetal.  Transition metals must be treated differently than main group metals because many transition metals can form ions with different charges.  For example, iron may form a +2 or a +3 ion.  In naming these compounds, we must have a way to distinguish between the different ions.  We do this by indicating the charge of the ion in the name.  The two iron ions would be named iron (II) and iron (III). 

Naming binary type II compounds is similar to naming type I, but the charge of the transition metal ion is included in the name.  So FeCl₂ and FeCl₃ would be named:

            FeCl₂   iron (II) chloride

            FeCl₃  iron (III) chloride

Remember that the Roman numerals are used only for compounds containing transition metals.  There are a few transition metals which only form a single ion (Zn, Ag, Cd).  For these metals, the Roman numeral is not used.

4.  Name the following compounds:

            a.  CuO

            b.  AgCl

            c.  Cr₂O₃

Ternary Compounds

Ternary compounds are composed of more than two elements.  They usually are composed of one or more polyatomic ions.  A polyatomic ion is a group of covalently bonded atoms bearing a charge.  This group of atoms is considered as a single unit –both in naming and in writing formulas.  Although there is a method for naming these polyatomic ions, it is easier at this point to memorize the most common ones.  Memorize the list below.  Be sure to learn the name, formula and charge of each ion.

Common Polyatomic Ions

These ternary compounds are named just like the type I and type II compounds discussed above, except the polyatomic ion names are used.  So, the names of the following compounds would be:

            Na₂CO₃           sodium carbonate

            Fe(NO₃)₃         iron (III) nitrate

5.  Name the following compounds:

            a.  Ba(OH)₂

            b.  NH₄Cl

            c.  Cu(CN)₂