Chapter 9Chemical Names and Formulas

Section 9.1Naming Ions

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Monatomic Ions

Ionic compounds consist of a positive metal ion and a negative nonmetal ion combined in a proportion such that their charges add up to a net charge of zero.

NaCl – consists of one Na+ and one Cl-.

Monatomic ions consists of a single atom with a positive or negative charge resulting from the loss or gain of one or more valence electrons.

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Monatomic Ions - CationsCations tend to lose valence electrons. (1+ charge – lose 1 electron, 2+ charge – lose 2 electrons, etc. )

When the metals in Groups 1A, 2A, and 3A lose electrons, they form cations with positive charges equal to their group number.

The name of the cations of the Group 1A, 2A and 3A are the same as the name of the metal, followed by the word ion or cation.

Na+ is sodium ion, Ca2+ is calcium ion, Al3+ is aluminum ion.

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Monatomic Ions - AnionsNonmetals tend to gain electrons to form anions, so the charge of a nonmetallic ion is negative.

The charge of any ion of a Group A nonmetal is determined by subtracting 8 from the group number.

Group 7A form anions with a 1- charge (7-8 = -1)

Anion names start with the stem of the element name and end in –ide.

Anion of fluorine is fluoride ion (F-), anion of chlorine is chloride ion (Cl-)

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Ions of Transition MetalsMany of the transition metals (Group 1B – 8B) form more than one cation with different ionic charges.

Two methods are used to name these ions.

1. Stock System – a roman numeral in parentheses is placed after the name of the element to indicate the numerical value of the charge.

Fe2+ is iron(II) ion Fe3+ is iron(III) ion.

2. Classical – name of the element is used to form the root name for the element.

Fe2+ is ferrous ion Fe3+ is ferric ion

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Symbols and Names of common Metal Ions

Cu + Copper (I) ion Cuprous ion

Cu 2+ Copper (II) ion Cupric ion

Hg + Mercury (I) ion Mercurous ion

Hg 2+ Mercury (II) ion Mercuric ion

Fe 2+ Iron (II) ion Ferrous ion

Fe 3+ Iron (III) ion Ferric ion

Cr 2+ Chromium (II) ion Chromous ion

Cr 3+ Chromium (III) ion Chromic ion

Mn 2+ Manganese (II) ion Manganous ion

Mn 3+ Manganese (III) ion Manganic ion

Co 2+ Cobalt (II) ion Cobaltous ion

Co 3+ Cobalt (III) ion Cobaltic ion

Pb 2+ Lead (II) ion Plumbous ion

Pb 4+ Lead (IV) ion Plumbic ion

Sn 2+ Tin (II) ion Stannous ion

Sn 4+ Tin (IV) ion Stannic ion

Cd 2+ Cadmium ion

Zn 2+ Zinc ion

Ag + Silver ion

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Polyatomic Ions

Polyatomic Ions are composed of more than one atom.

Sulfate ions (SO4 2-) is composed of one sulfur atom and

four oxygen atoms.

Polyatomic ions are a tightly bound group of atoms that behave as a unit and carry a charge.

The names of most polyatomic anions end in –ite or –ate.

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Common Polyatomic Ions

Charge 1 +

NH4 + Ammonium

Charge 1 ─

ClO ¯ Hypochlorite OH ¯ Hydroxide

ClO2 ¯ Chlorite CH3COO ¯ Acetate

ClO3 ¯ Chlorate CN ¯ Cyanide

ClO4 ¯ Perchlorate OCN ¯ Cyanate

lO2 ¯ Iodite HSO3 ¯ Bisulfite

lO3 ¯ Iodate HSO4 ¯ Bisulfate

lO4 ¯ Periodate HCO3 ¯ Bicarbonate

NO2 ¯ Nitrite BrO3 ¯ Bromate

NO3 ¯ Nitrate MnO4 ¯ Permanganate

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Common Polyatomic Ions

Charge 2 ─

CO3 2− Carbonate CrO4 2− Chromate

SO3 2− Sulfite Cr2O7 2− Dichromate

SO4 2− Sulfate C2O4 2− Oxalate

S2O3 2− Thiosulfate SiO3 2− Silicate

O2 2− Peroxide

Charge 3 ─

PO3 3− Phosphite AsO3 3− Arsenite

PO4 3− Phosphate AsO4 3− Arsenate

BO3 3− Borate

Charge 4 ─

P2O7 4− Pyrophosphate

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Section 9.2

Naming Ionic Compounds

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Naming Binary Ionic Compounds

A binary compound is composed of two elements and can be either ionic or molecular (covalent).

To name any binary ionic compound, place the cation name first, followed by the anion name.

Cs2O is cesium oxide NaBr is sodium bromide

Cu2O is copper(I) oxide CuO is copper(II) oxide

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Writing Formulas Binary Ionic Compounds

Write the symbol of the cation and then the anion. Add whatever subscripts are needed to balance the charges.

The positive charge of the cation must balance the negative charge of the anion so that the net ionic charge of the formula is zero.

K+ + Cl- KCl

Ca2+ + Br - CaBr2

Fe3+ + O2- Fe2O3

Use the crisscross method – the numerical value of the charge of each ion is crossed over and becomes the subscript for the other ion.

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Writing Formulas Polyatomic Ionic Compounds

An –ate or –ite ending on the name of a compound indicates that the compound contains a polyatomic anion that includes oxygen.

Write the symbol for the cation followed by the formula for the polyatomic ion and balance the charges.

Ca2+ + NO3- Ca(NO3)2

Sr2+ + SO32- SrSO3

Li+ + CO32- Li2CO3

Use the crisscross method – the numerical value of the charge of each ion is crossed over and becomes the subscript for the other ion.

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Naming Polyatomic Ionic Compounds

First recognize that the compound contains a polyatomic ion.

State the cation first and then the anion

NaClO

sodium hypochlorite

(NH4)2C2O4

ammonium oxalate

Li2CO3

lithium carbonate14

Section 9.3

Naming and Writing Formulas for

Molecular Compounds

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Naming Molecular Compounds

Binary ionic compounds are composed of the ions of two elements, a metal and a nonmetal.

Binary molecular compounds are composed of two elements, two nonmetals and they are not ions.

Binary molecular compounds are composed of molecules, not ions, so ionic charges cannot be used to write formulas or to name them.

In addition, when two nonmetallic elements combine, they often do so in more than one way. (CO, CO2)

Prefixes in the names of binary molecular compounds help distinguish compounds containing different amounts of the same two elements. 16

Naming Molecular CompoundsThe prefix in the name of a binary molecular compound tells how many atoms of each element are present in each molecule of the compound.

Prefix Number

mono- 1

di- 2

tri- 3

tetra- 4

penta- 5

hexa- 6

hepta- 7

octa- 8

nona- 9

deca- 10 17

Naming Molecular Compounds

The names of all binary molecular compounds end in –ide.

CO is carbon monoxide

CO2 is carbon dioxide

If just one atom of the first element is in the formula, omit the prefix mono-

•Name the elements in order listed in the formula

•Use prefixed to indicate the number of each kind of atom

•The suffix of the name of the second element is –ide.

N2O is dinitrogen monoxide

SF6 is sulfur hexafluoride.18

Writing FormulasMolecular Compounds

Use the prefixes in the name to tell you the subscript of each element in the formula.

Then write the correct symbols for the two elements with the appropriate subscripts.

Dinitrogen tetraoxide

N2O4

Diphosphorus trioxide

P2O3

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Section 9.4

Naming and Writing Formulas for

Acids and Bases

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Naming Acids

Acid is a compound that contains one or more hydrogen atoms and produces hydrogen ions (H+) when dissolved in water.

When naming acids, the acid consists of an anion combined with as many hydrogen ions as needed to make the molecule electrically neutral.

The general chemical formulas of acids is HnX.

X is a monatomic or polyatomic anion

n is a subscript indication the number of hydrogen ions combined with the anion.

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Naming Acids

Three rules are used to name acids. The name depends on the name of the anion and its suffix (-ide, -ite, -ate)

1. a. When the name of the anion ends in –ide, the acid name begins with the prefix hydro-.

b. The stem of the anion has the suffix –ic and is followed by the word acid.

H+ + Cl - HCl

Hydrogen ion chloride ion hydrochloric acid

H+ + S2- H2S

Hydrogen ion sulfide ion hydrosulfuric acid22

Naming Acids

Three rules are used to name acids. The name depends on the name of the anion and its suffix (-ide, -ite, -ate)

2. a. When the anion name ends in –ite, the acid name is the stem of the anion with the suffix –ous, followed by the word acid

H+ + SO32- H2SO3

Hydrogen ion sulfite ion sulfurous acid

H+ + CIO2- HCIO2

Hydrogen ion chlorite ion chlorous acid

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Naming Acids

Three rules are used to name acids. The name depends on the name of the anion and its suffix (-ide, -ite, -ate)

3. a. When the anion name end in –ate, the acid name is the stem of the anion with the suffix –ic followed by the word acid.

H+ + NO3- HNO3

Hydrogen ion nitrate ion nitric acid

H+ + SO42- H2SO4

Hydrogen ion sulfate ion sulfuric acid

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Writing Formulas for Acids

Use the rules for writing the names of acids in reverse to write the formula for acids.

Hydrobromic acidHydro indicates the bromide ion

HBr

Phosphorous acid-ous indicates the phosphite ion

H3PO3

phosphoric acid -ic and beginning with the anion name indicates the phosphate ion

H3PO425

BasesA base is an ionic compound that produced hydroxide

ions (OH-) when dissolved in water.

Bases are named the same way as other ionic compounds – the name of the cation is followed by the name of the anion.

NaOH is sodium hydroxide

To write the formulas for bases, write the symbol for the cation followed by the formula for the hydroxide ion. (then use the crisscross method to write the formula as you do as you do for any ionic compound)

Aluminum hydroxide – Al3+ + OH- Al(OH)3

Ammonium hydroxide – NH4+ + OH- NH4OH

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