Classification of Compounds (nomenclature)

International Union of Pure and Applied Chemistry IUPAC

Binary Ionic: two elements, a metal and non -metal. NaCl, KI, AlCl₃, CaF₂

Ternary ionic: three elements, at least one metal and a nonmetal. KNO₃, Al(NO₃)₃, MgSO₄

Binary molecular: two elements that are both nonmetals. H₂O, NH₃, CO₂

Binary Acids: compounds containing hydrogen and one other nonmetal. HCl, HI, H₂S

Ternary oxyacids: compounds containing hydrogen a nonmetal and oxygen. HNO₃, H₂SO₄, H₃PO₄

Nomenclature of Monoatomic Cations

Main-group metals usually form one cation. Cations are named for the parent metal followed by the word ion. Na⁺ ( sodium ion) Al³⁺ ( aluminum ion)

Transition metals often form more than one cation.

Ex. Fe²⁺ and Fe³⁺

It is necessary to specify the charge. Iron(II) and iron(III) ion. Cu⁺ is named copper(I) ion and Cu²⁺ is named copper(II) ion. This is called the Stock system.

Note that Al³⁺, Zn²⁺, and Cd²⁺ are exceptions (have fixed ionic charge) and do not require Roman numerals.

Latin System or Suffix System

This system takes the Latin name of the metal and adds an -ous or ic suffix. The lower of the two ionic charges receives the -ous suffix, and the higher charge recives the -ic sufix.

The Latin name for iron is ferrum. Fe²⁺ is ferrous while Fe³⁺ is ferric.

The Latin name for copper is cuprum. Add ous or ic to the cupr- stem.

Cu⁺ cuprous ion. Cu²⁺ cupric ion.

IUPAC convention for nonmetal ions use using the nonmetal stem + ide suffix.

Anion IUPAC Name

Br^- bromide ion

Cl^- chloride ion

F^- fluoride ion

I^- iodide ion

N^3- nitride ion

O^2- oxide ion

P^3- phosphide ion

Polyatomic ions

NH₄⁺ ammonium ion

C₂H₃O₂^- acetate ion

CO₃^2- carbonate ion

ClO₃^- chlorate ion

ClO₂^- chlorite ion

OH^- hydroxide ion*

CN^- cyanide ion*

SO₄^2- sulfate ion

SO₃^2- sulfite ion

NO₃^- nitrate ion

Nomenclature of Monoatomic Cations

Main-group metals usually form one cation. Cations are named for the parent metal followed by the word ion. Na⁺ ( sodium ion) Al³⁺ ( aluminum ion)

Most polyatomic anions end in an -ate or ite suffix. The -ite suffix has one less oxygen than that for the -ate ending.

There are three exceptions to memorize, OH^-, CN^- (ide) and the ammonium cation (NH₄⁺).

Hypo means under and per means over.

ClO^- hypochlorite ion

ClO₂^- chlorite ion

ClO₃^- chlorate ion

ClO₄^- perchlorate ion

Writing Chemical Formulas

A formula unit is the simplest representative particle in an ionic compound. The total positive charge must equal the total negative charge for the unit to be neutral.

CaCl₂ contains one Ca²⁺ and two Cl^-

Binary compounds

Name the most metallic (less electronegative) element first and the more electronegative element second.

The less metallic (more electronegative) element is named by adding an "-ide" suffix to the element’s unambiguous stem.

Si silic P phosph S sulf F fluor

Se selen Cl chlor

Te tellur Br brom

Compounds composed of nonmetals only

Nearly all binary molecular compounds involve two nonmetals bonded together. Although many nonmetals can exhibit different ionic charges (oxidation numbers), their oxidation numbers properly are not indicated by Roman numerals or suffixes. Instead, elemental proportions are indicated by using a prefix system for both elements.

Greek prefixes are used to indicate the number of each atom

Atoms Prefix Atoms Prefix

1 mono 6 hexa

2 di 7 hepta

3 tri 8 acta

4 tetra 9 nona

5 penta 10 deca

Formula Name

SO₂ sulfur dioxide

SO₃ sulfur trioxide

N₂O₄ dinitrogen tetroxide

Cl₂O₇ dichlorine heptoxide

CS₂ carbon disulfide

As₄O₆ tetraarsenic hexoxide

Compounds formed between metals and nonmetals.

Binary ionic compounds contain metal cations and nonmetal anions. The cation is named first and the anion second according to the rule described previously.

Formula Name

KBr potassium bromide

CaCl₂ calcium chloride

NaH sodium hydride

RbS rubidium sulfide

Al₂Se₃ aluminum selenide

SrO strontium oxide

Metals with multiple ionic charges

(oxidation states)

The preceding method is sufficient for naming binary ionic compounds containing metals that exhibit only one oxidation number other than zero. Most transition elements, and few of the more electronegative representative metals exhibit more than one oxidation number. To distinguish among all possibilities, the oxidation number of the metal is indicated by a Roman numeral in parentheses following its name.

Charge

Formula on metal Name

Cu₂O +1 copper(I) oxide

FeS +2 iron(II) sulfide

Compounds containing 3 or more atoms

Formula Name

NH₄I ammonium iodide

Ca(CN)₂ calcium cyanide

NaOH sodium hydroxide

NH₄CN ammonium cyanide

Cu(ClO₃)₂ copper(II) chlorate or

cupric chlorate

Fe₂(SO₄)₃ iron(III) sulfate or

ferric sulfate

Aqueous solutions

Binary acids are compounds in which H is bonded to the more electronegative nonmetals. These compounds act as acids when dissolved in water. The compounds are name as typical binary compounds. Their aqueous solutions are named by modifying the characteristic stem of the nonmetal with the prefix "hydro-" and the suffix "-ic" followed by the word "acid."

Name of Aqueous solutions

Formula Name of Compound solution

HCl hydrogen chloride hydrochloric acid

HF hydrogen fluoride hydrofluoric acid

H₂S hydrogen sulfide hydrosulfuric acid

HCN hydrogen cyanide hydrocyanic acid

For ternary and higher compounds, the word "hydrogen" is dropped, and the name of the polyatomic ion is used. "-ate" is replaced with "-ic" and "-ite" is replaced with "-ous"

Formula Name of Compound Aqueous solution

HNO₂ hydrogen nitrite nitrous acid

HNO₃ hydrogen nitrate nitric acid

H₂SO₄ hydrogen sulfate sulfuric acid

H₃PO₃ hydrogen phosphite phosphorous acid

H₃PO₄ hydrogen phosphate phosphoric acid