Naming Ternary Ionic, Covalent and Acid Compound

A ternary compound is one containing three elements, from figure 2 and 2,1 in recent article, it should be apparent that ternary compounds are classified in a manner similar to binary compounds. First decide if the ternary compound is ionic or covalent. If it is ionic , check to see if the metal has a fixed or variable oxidation number. If it is covalent, determine if it is an acid or not.

We shall concentrate on naming ternary compounds composed of a metal and a polyatomic ion ( ionic ), and of hydrogen bonded to a polyatomic ion ( acid ).

Ionic ternary compounds are named like binary compounds, except that a polyatomic ion name is found in place of either the metal ion or nonmetal ion name. Study the table below and memorize the 12 polyatomic ions listed. Once these 12 polyatomic ions are learned, naming ternary compounds is simplified. When you learn ions, don’t forget about their charges. It is of no value to learn the ions without their charges !

Name of polyatomic ion Formula
Hydroxide OH-
Sulfate SO42-
Nitrate NO3-
Phosphate PO43-
Chlorate ClO3-
Cyanide CN-
Permanganate MnO4-
Carbonate CO32-
Chromate CrO42-
Borate BO33-
Acetate C2H3O2-
Ammonium NH4+

A. Naming Ternary Ionic Compound

When naming an ionic ternary compound , first determine if the metal in the ternary compound has a fixed or variable oxidation number. Depending on what metal is found, the compound is named in a similar manner to an ionic binary compound except there is a polyatomic ion name in the formula.

Lets illustrate the naming of ionic ternary compounds by considering Co(NO3)2 . Cobalt is a transition metal with a variable oxidation state . thus determine the oxidation state of Co and write its oxidation state in parentheses Cobalt(II). Then identify the polyatomic ion, NO3- , nitrate and add it to the metal’s name Cobalt(II)nitrate.

Co(NO3)2 = Cobalt(II)nitrate

Cobalt’s oxidation state is obtained by knowing the charge on the nitrate ion, -1. Since there are two nitrate ions, the cobalt exists in the +2 oxidation state.

Example :

Name the following compounds using the stock system a. K2CrO4 b. (NH4)2S c. FeCO3 d. Mn3(PO4)2

Answer :

a. K2CrO4 . The metal is potassium , an alkali metal with a fixed oxidation state , and the polyatomic ion is chromate. Thus :

K2CrO4 = Potassium chromate

A number is not written after potassium because it only exist in one oxidation state +1

b. (NH4)2S. In this compound , we find the ammonium ion in place of a metal, and the nonmetal is sulfur. Remove sulfur’s ending and attach ide.

(NH4)2S = Ammonium Sulfide

c. FeCO3. Iron is a metal with a variable oxidation state , consequently, the name must indicate which oxidation state iron is in. Given that carbonate, CO32-, has 2- charge , then iron’s oxidation number is +2 in order for the sum to equal zero. Accordingly :

FeCO3 = Iron(II)carbonate

d. Mn3(PO4)2. Once again, the oxidation state of the metal has to be expressed because manganese exists in a variety of states. Phosphate has a charge of 3-, therefore two phosphates have a total charge 6-. So the total oxidation number for the three Mn atoms is +6, or each Mn has an oxidation number of +2.

Mn3(PO4)2 = Manganese(II)phosphate

Example II

Write the fomulas for a.Zinc(II)hydroxide b. Silver(I)cyanide and c. Cobaltic Sulfate.

Answer :

a. Zinc(II)hydroxide , Zinc(II) is Zn2+ , and hyrdroxide is OH-. To produce a compound with a zero oxidation state, two hydroxides are required per zinc ion.

Zn2+ OH-

Zinc(II)hydroxide = Zn(OH)2

b. Silver(I)cyanide. Silver(I) is Ag+ and cyanide is CN-. Since they have equal but opposite charges, they are combined in a 1-to-1 ratio.

Ag+ CN-

Silver(I)cyanide = AgCN

c. Cobaltic Sulfate. Cobaltic represent the higher of cobalt’s oxidation states, Co3+. Sulfate’s formula is SO42-. Here we have to find the lowest common denominator between 3 and 2 ; it is 6. Cobaltic sulfate becomes Co2(SO4)3.

Co3+ SO42-

Cobaltic Sulfate = Co2(SO4)3

A group of polyatomic ions exists with one less oxygen than some of those listed in table 3 below . For example , in addition to sulfate , SO42- there is an an ion with the formula SO32-. How is this ion named ? If a polytatomic ion has one less oxygen than the ion ending in ate, it is given an ite ending. Consequently, SO32- is the sulfite ion since it has one less oxygen than sulfate , SO42- , look on the table below, there is found list other examples of ite oxyanions :

Oxyanion ion Name
SO42- Sulfate
SO32- Sulfite
NO3- Nitrate
NO2- Nitrite
PO43- Phosphate
PO33- Phospite
AsO43- Arsenate
AsO33- Arsenite
SeO42- Selenate
SeO32- Selenite

Once the formula for the ate ion is learned , it is only necessary to subtract an oxygen from the formula and replace the ending of the name with ite to obtain the correct formula and name of the ite ion.

Example :

Write the stock name for a. Fe3(PO3)2 and b. Ba(NO2)2

Answer :

a. Fe3(PO3)2 . Looking at the oxyanion , we notice that it has one less oxygen than phosphate , PO43- ; thus it is the phosphite ion PO33- . since there are two phosphite ions in the formula, each with a charge of 3-, their total charge is 6-. Each iron has a charge of 2+ ( 3 x 2+ = 6+ ) to balance the charge of the phosphite ions. Accordingly , the name of Fe3(PO3)2 is iron(II)phosphite.

Fe3(PO3)2 = iron(II)phosphite

b. Ba(NO2)2. Barium is an element in group IIA ; thus it has a fixed charge of +2. NO2- has one less oxygen than nitrate, NO3- , nitrate; so its name is nitrite, thus :

Ba(NO2)2 = Barium nitrite

B. Naming Binary and Ternary Covalent Compounds

Covalent compounds are formed when two or more nonmetals combine.

Nonmetal + Nonmetal > Covalent compound

Frequently encountered covalent compounds include water, H2O, ammonia, NH3, carbon dioxide, CO2, and sulfur dioxide , SO2. In each of these binary examples of covalent compounds two different nonmetallic elements are chemically combined together.

Naming binary covalent compounds is somewhat different from naming ionic compounds. If there is only one atom of the nonmetal that appears first in the formula , write its name with no change . As In naming ionic compounds replace the ending of the second non metal with ide. In adition , a prefix indicating the quantity of that element in the compound is also written .

Consider CO2 as an example . it is named by writing the first nonmetal, carbon, and then modifying the second nonmetal , oxygen, by adding the prefix di, meaning two and dropping the ending ygen and attaching ide. Hence , CO2 is carbon dioxide.

CO2 = Carbon ( di + oxygen – ygen + ide )

= Carbon Dioxide

An additional prefix is needed in the name of covalent compounds because nonmetals can combine in a variety of ways. For instance, there is a second oxide of carbon, carbon monoxide, CO. the prefix mono or just mon is added to indicate that this oxide of carbon only contain one oxygen. Look on table 3 below ! There is found list the prefixes that are utilized in naming covalent compounds.

Prefix Number of atoms indicated
Mono 1
di 2
Tri 3
Tetra 4
Penta 5
hexa 6
Hepta 7
Octa 8
Nona 9
Deca 10

If there are two or more of the first nonmetal in a covalent compound. It is necessary to add a prefix indicating how many are in the formula . Example on table 3 illustrates naming different types of covalent compounds.

Example :

Name the following compounds a. SCl2 b. N2O c. P2O5

Answer :

a. SCl2 = Sulfur ( di + chlorine-ine + ide ) = sulfur dichloride
b. N2O = ( di + nitrogen ) + ( oxygen – ygen + ide ) = dinitrogen oxide
c. P2O5 = ( di + phosphorus ) + ( pent + oxygen – ygen + ide ) = diphosphorus pentoxide

Covalent compounds are markedly different from ionic compounds. Most covalent compounds are either liquids or gases; some are rather soft solids. Compared with average ionic compounds , covalent compounds have lower melting and boiling points , and lower densities. Covalent compound are poor conductors of both heat and electricity.

A. Naming Binary Covalent Compound Metals-Non Metals

Two write the formula of an ionic compound , write each ion with its correct oxidation state and then determine the quantity of each ion that produces a zero oxidation state for the compound.
What is the formula of chromium(III)oxide ? given the stock formula, the oxidation state of the metal is readily obtained. Oxygen belongs to group VI A and has a -2 oxidation number in binary compounds. Write both elements with their oxidation numbers.

+3 2-

Cr O

Since the sum of all oxidation numbers adds up to zero , ask yourself what number or Cr and O atoms would give the same total oxidation numbers. This is easily accomplished by finding the lowest common multiple for the two oxidation numbers. For Cr and O the lowest common multiple is 6.

Then, divide each individual oxidation number into the lowest common multiple to obtain the correct formula subscript.

Lowest common multiple = 6

The two Cr atoms and three O atoms are found in Chromium(III)oxide

Example :

Write the formulas for each of the following a. Cobaltous oxide b. Lead(II)chloride c. Titanium(III)sulfide

Answer :

a. Cobaltous Oxide . = CoO

b. Lead(II)chloride = PbCl2

c. Titanium(III)sulfide = Ti2S3

B. Naming Binary Ionic Acid

Various covalent binary hydrogen compounds are classified as acids. When dissolved, acids ionize and add hydrogen ions, H+, and anions to water. In the following equation, hyphothetical acid HA breaks up into H+ and A- ( anion ) :

HA > H+ + A-

To name binary acid , the prefix hydro is added to the nonmetal name, the ending is droped , and ic acid is attached in its place.

Acid Name = hydro + nonmetal – ending - ic acid

Examples of binary acids include hydrochloric acid HCl, Hydroflouric acid HF and etc.

Okay guys, that’s all about naming binary and covalent compound, In the next article we will discuss about naming covalent or polyatomic acid .

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