What is the name of this ionic compound (Fr2SO4)

3.5: Ionic Compounds- Formulas and Names

Last updatedAug 25, 2020

3.4: An Atomic-Level Perspective of Elements and Compounds

3.6: Molecular Compounds- Formulas and Names

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6.9: Binary Ionic Compounds and Their Properties

6.18: Ionic Compounds Containing Polyatomic Ions

Learning Objectives

Derive names for common types of inorganic compounds using a systematic approach

Nomenclature, a collection of rules for naming things, is important in science and in many other situations. This module describes an approach that is used to name simple ionic and molecular compounds, such as NaCl, CaCO3, and N2O4. The simplest of these are binary compounds, those containing only two elements, but we will also consider how to name ionic compounds containing polyatomic ions, and one specific, very important class of compounds known as acids (subsequent chapters in this text will focus on these compounds in great detail). We will limit our attention here to inorganic compounds, compounds that are composed principally of elements other than carbon, and will follow the nomenclature guidelines proposed by IUPAC. The rules for organic compounds, in which carbon is the principle element, will be treated in a later chapter on organic chemistry.

Ionic Compounds

To name an inorganic compound, we need to consider the answers to several questions. First, is the compound ionic or molecular? If the compound is ionic, does the metal form ions of only one type (fixed charge) or more than one type (variable charge)? Are the ions monatomic or polyatomic? If the compound is molecular, does it contain hydrogen? If so, does it also contain oxygen? From the answers we derive, we place the compound in an appropriate category and then name it accordingly.

Compounds Containing Only Monatomic Ions

The name of a binary compound containing monatomic ions consists of the name of the cation (the name of the metal) followed by the name of the anion (the name of the nonmetallic element with its ending replaced by the suffix –ide). Some examples are given in Table  3.5.2 .

Table  3.5.1 : Names of Some Ionic Compounds

NaCl, sodium chlorideNa2O, sodium oxide

KBr, potassium bromideCdS, cadmium sulfide

CaI2, calcium iodideMg3N2, magnesium nitride

CsF, cesium fluorideCa3P2, calcium phosphide

LiCl, lithium chlorideAl4C3, aluminum carbide

Compounds Containing Polyatomic Ions

Compounds containing polyatomic ions are named similarly to those containing only monatomic ions, except there is no need to change to an –ide ending, since the suffix is already present in the name of the anion. Examples are shown in Table  3.5.2 .

Table  3.5.2 : Names of Some Polyatomic Ionic Compounds

KC2H3O2, potassium acetate(NH4)Cl, ammonium chloride

NaHCO3, sodium bicarbonateCaSO4, calcium sulfate

Al2(CO3)3, aluminum carbonateMg3(PO4)2, magnesium phosphate

Ionic Compounds in Your Cabinets

Ionic CompoundUse

NaCl, sodium chlorideordinary table salt

KI, potassium iodideadded to “iodized” salt for thyroid health

NaF, sodium fluorideingredient in toothpaste

NaHCO3, sodium bicarbonatebaking soda; used in cooking (and as antacid)

Na2CO3, sodium carbonatewashing soda; used in cleaning agents

NaOCl, sodium hypochloriteactive ingredient in household bleach

CaCO3 calcium carbonateingredient in antacids

Mg(OH)2, magnesium hydroxideingredient in antacids

Al(OH)3, aluminum hydroxideingredient in antacids

NaOH, sodium hydroxidelye; used as drain cleaner

K3PO4, potassium phosphatefood additive (many purposes)

MgSO4, magnesium sulfateadded to purified water

Na2HPO4, sodium hydrogen phosphateanti-caking agent; used in powdered products

Na2SO3, sodium sulfitepreservative

Table  3.5.3 : Names of Some Transition Metal Ionic Compounds

Transition Metal Ionic CompoundName

FeCl3iron(III) chloride

Hg2Omercury(I) oxide

HgOmercury(II) oxide

Cu3(PO4)2copper(II) phosphate

Naming Ionic Compounds

Name the following ionic compounds, which contain a metal that can have more than one ionic charge:

Fe2S3

CuSe

GaN

CrCl3

Ti2(SO4)3

Solution

The anions in these compounds have a fixed negative charge (S2−, Se2− , N3−, Cl−, and  SO2−4 ), and the compounds must be neutral. Because the total number of positive charges in each compound must equal the total number of negative charges, the positive ions must be Fe3+, Cu2+, Ga3+, Cr4+, and Ti3+. These charges are used in the names of the metal ions:

iron(III) sulfide

copper(II) selenide

gallium(III) nitride

chromium(III) chloride

titanium(III) sulfate

Exercise  3.5.1  

Write the formulas of the following ionic compounds:

(a) chromium(III) phosphide

(b) mercury(II) sulfide

(c) manganese(II) phosphate

(d) copper(I) oxide

(e) chromium(VI) fluoride

Answer

(a) CrP; (b) HgS; (c) Mn3(PO4)2; (d) Cu2O; (e) CrF6

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