Ionic compounds contain positive and negative ions. They are held together by electrostatic...

• Ionic compounds contain positive and negative ions. They are held together by electrostatic attraction. Most of the negative ions have only one possible oxidation state. This is not the case with the positive ions. Many of these ions have several oxidation states. The use of prefixes in naming these compounds could lead to confusion. Consequently a new method “the stock system” is very specific in the naming of ionic compounds.

Ionic compounds may contain (1) a metal and a non-metal, (2) a metal and a polyatomic ion or (3) a positive polyatomic ion and a negative polyatomic ion. No matter which is used the procedure for the “stock system is the same. The most difficult issue when using the “stock system” is the memorization of polyatomic ions and their oxidation states. The most common must be committed to memory. Look for trends....

• Note location of metals (lower left) and non-metals (upper right) on the periodic chart. Metaloids which border the stair-step transition line may behave as either positive or negative ions.

For example the oxy-salts of chlorine, bromine and iodine have many trends in common. Look for them below……

perchlorate ClO4-1

chlorate ClO3-1

chlorite ClO2-1

hypochlorite ClO-1

perbromate BrO4-1

bromate BrO3-1

bromite BrO2-1

hypobromite BrO-1

periodate IO4-1

iodate IO3-1

iodite IO2-1

hypoiodite IO-1

The next table contains the polyatomic ions that need to be committed to memory. Remember to learn the name, formula and oxidation number

POLYATOMIC IONS

Ions with -1 chargeperbromate BrO4

-1

bromate BrO3-1

bromite BrO2-1

hypobromite BrO-1

perchlorate ClO4-1

chlorate ClO3-1

chlorite ClO2-1

hypochlorite ClO-1

periodate IO4-1

iodate IO3-1

iodite IO2-1

hypoiodite IO-1

nitrate NO3-1

nitrite NO2-1

hydroxide OH-1

cyanide CN-1

thiocyanate SCN-1

acetate C2H3O2-1

Permanganate MnO4

-1

bicarbonate HCO3-1

Ions with a -2 Chargecarbonate CO3

-2

phthalate C8H4O4-2

sulfate SO4-2

sulfite SO3-2

chromate CrO4-2

dichromate Cr2O7-2

oxalate C2O4-2

peroxide O2-2

Ions with a -3 Chargephosphate PO4

-3

phosphite PO3-3

arsenate AsO4-3

Ions with +1 chargeammonium ion

NH4+1

POLYATOMIC IONS


-1

bromate BrO3-1

bromite BrO2-1

hypobromite BrO-1

perchlorate ClO4-1

chlorate ClO3-1

chlorite ClO2-1

hypochlorite ClO-1

periodate IO4-1

iodate IO3-1

iodite IO2-1

hypoiodite IO-1

nitrate NO3-1

nitrite NO2-1

hydroxide OH-1

cyanide CN-1

thiocyanate SCN-1

acetate C2H3O2-

1

Permanganate MnO4-1

bicarbonate HCO3-1


-2

phthalate C8H4O4-

2

sulfate SO4-2

sulfite SO3-2

chromate CrO4-2

dichromate Cr2O7-2

oxalate C2O4-2

peroxide O2-2


-3

phosphite PO3-3

arsenate AsO4-3


NH4+1

BrO4-1

BrO3-1

BrO2-1

BrO-1

ClO4-1

ClO3-1

ClO2-1

ClO-1

IO4-1

IO3-1

IO2-1

IO-1

Ions with -1 chargeperbromatebromatebromitehypobromiteperchloratechloratechloritehypochloriteperiodateiodateioditehypoiodite

It is also important to memorize the oxidation of the monatomic ions that

have fixed oxidation numbers (positive or negative). In particular, those

from groups 1A, 2A, 3A, 4A, 5A, 6A, 7A, 8A and the elements: Zn, Cd and Ag. Use the following periodic chart to determine their oxidation numbers. Just click on the element symbol…

N

Elements with Fixed Oxidation Numbers

La Hf Ta Re OsCe Ba Tl Pb Bi Po At RnIr Pt Au Hg

Y Zr Nb Mo Tc RuRb Sr In Sn Sb Te I XeRh Pd Ag Cd

Sc Ti V Cr Mn FeK Ca Ga Ge As Se Br KrCo Ni Cu Zn

Al Si P S Cl ArNa Mg

B C O F NeLi Be

H H He

Ac Rf Db Sg Rh HsFr Ra Mt

+1+2+31A

2A

8A

0-4-3-2-17A

6A5A4A3A

W

Nd Pm Sm Eu Gd TbCe Pr Yb LuDy Ho Er Tm

Np Am Cm BkTh Pa No LrCf Es Fm MdU Pu

Click on element to see its oxidation number(s)

Next Slide

Naming Ionic Compounds• The positive ion (usually a metal) is named first while

the negative ion (a non-metal or a polyatomic ion) is named last.

• The charge on the negative ion is used to determine the charge on the positive ion. The oxidation state of a compound is always zero, otherwise it would be a polyatomic ion. In-order for the total oxidation state to be zero the total positive charge must equal the total negative charge. A simple algebraic equation can be used to determine the charge on a single metal ion. This charge is expressed as a “Roman Numeral” in parenthesis that immediately follows the name of the metal.

• If the positive ion is one that has a fixed oxidation number then no Roman Numeral is used. Everyone should know the charge of that ion. These include metals in group 1A, 2A and the specific metals: Al, Zn, Cd & Ag.

• If the ionic compound is binary it will end in “-ide”. However, not all compounds that end in “-ide” are binary. For example sodium hydroxide has the formula…NaOH (three different kinds of atoms).

• If the negative ion is a polyatomic ion the compound is no longer binary. The ending will be that carried by the polyatomic ion. These endings are either “-ate” or “-ite.”

• Hydrated compounds are named using a combination of both the stock system and prefixes. A prefix is used to denote the number of water molecules attached to the ionic formula. “hydrate” is used as the name indicating that water is attached. For example, copper(II) sulfate pentahydrate has the formula CuSO4

.5H2O

Examples #1- Formulas to Names

CuSO3

copper

I’m a polyatomi

c ion

1. Write the names of the ions

Final Name

sulfite(II)

x

X + (- 2) = 0

X = +2

Cu SO3

= 0

You must know the charge on the sulfite ion is -2

The sum of the positive and negative charges must equal zero

2. Determine the charge of the positive ion

-

2

+2 +2

Next

+2


KMnO4

potassium

I’m a polyatomi

c ion



Final Name

permanganate

Kx (MnO4)-1 = 0

X + (-1) = 0

(I)

X = +1

If the positive ion has a fixed charge, it is not shown


NH4NO3

ammonium

I’m a polyatomi

c ion



Final Name

nitrate(I)

NH4x (NO3)-1 = 0

X + (-1) = 0

X = +1



SnF2

tin

I’m not a polyatomi

c ion



Final Name

fluoride(II)

Snx (F-1)2 = 0

X + 2(-1) = 0

X = +2


Ba(ClO4)2

barium

I’m a polyatomi

c ion



Final Name

perchlorate(II)

Bax (ClO4-1)2 = 0

X + 2(-1) = 0

X = +2



Cu2S

copper

I’m not a polyatomi

c ion



Final Name

sulfide(I)

2Cux (S)-2 = 0

2X + (-2) = 0

X = +1


Cu2S

copper

1.Write the names of the ions

Final Name

sulfide(I)

x

2X + (- 2) = 0

2X = +2

(Cu )2 S

You must know the charge on the sulfide ion is -2

The sum of the positive and negative charges must equal zero


-2

+2 +2

Next

+1

2 2

X = +1


Na2Cr2O7

sodium

I’m a polyatomi

c ion



Final Name

dichromate(I)

2(Nax)(Cr2O7)-2 = 0

2X + (-2) = 0

X = +1



Na2O2

sodium

I’m a polyatomi

c ion



Final Name

peroxide(I)

2(Nax) (O2-2) = 0

2X + (-2) = 0

X = +1


FePO3 .3H2O


iron

I’m a polyatomi

c ion



Final Name phosphite(III)

Fex (PO3 -3) = 0

X + (-3) = 0

X = +3

hydrate

I’m a hydrated compound, this

part will be named last

.3H2O3

tri


LiCN

lithium

I’m a polyatomi

c ion



Final Name

cyanide(I)

Lix (CN-1) = 0

X + (-1) = 0

X = +1


Writing Ionic Formulas• It is easier to write the formula of an

ionic compound from its name than the reverse. The oxidation state (or charge) of all compounds is zero. This is the first naming system that requires the balancing of the positive and negative charges such that the result is zero.

• The oxidation number of the negative ion must be memorized in all cases. Refer to the table of polyatomic ions.

• The positive ion is either one of those that has a fixed oxidation number or a “Roman Numeral” will follow the positive ion. Metals that have only one oxidation number must be memorized. These include metals in group 1A, 2A and the specific metals: Al, Zn, Cd & Ag. If there is a “Roman Numeral” is in the name, it represents the charge of one of the positive ions.

• Remember the total positive charge must equal to the total negative charge. The result is a compound which has no charge. Multiply the oxidation numbers of both the positive and negative ions by a number that will result in the smallest identical numbers of positive and negative charges. These multipliers represent the number of atoms of each ion required to give a neutral ionic compound.

• The formulas of hydrated compounds are written using a combination of both the stock system and prefixes. A prefix is used to denote the number of water molecules attached to the ionic formula. “hydrate” is used as the name indicating that water is attached. For example, copper(II) sulfate pentahydrate has the formula CuSO4

.5H2O (notice a dot separates the ionic compound from the water of hydration)

Example #1-Names to Formulas

aluminum chloride

AlCl3

2. Determine number of ions

1. Write symbols of elements

Final Formula

(Al )x(Cl-1)y= 0

3X = 1y

X(+3) + y(-1) = 0

Y 3X 1=

1Choose the lowest set of integers that

satisfies the equationIf there is only one atom

the “1” is not shown

If there is no Roman Numeral, you need to know the fixed oxidation number of the positive ion.

+3


What is the Lowest Common Multiple “LCM” of 3 and 1. Do not worry about the sign(+/-)

Next


aluminum chloride

Al Cl3



Final Formula

X(+3) + y(-1) = 0

1

For aluminum, a 1 is multiplied

times the +3 to give a +3 charge

If there is only one atom the “1” is not shown

If there is no Roman Numeral, you must know the oxidation number of the positive ion.

+3

If there is no Roman Numeral, you must know the oxidation number of the positive ion.


(Al )x(Cl-1)y


For chloride, a 3 is multiplied

times the -1 to give a -3 charge

1(+3) + 3(-1) = 0

Remember all compounds are neutral, thus

the total positive charge must equal the

total negative charge

Next

This formula says that the +3 charge of one Alatom will cancel the-3

charge from 3 Cl atoms


cobalt(II) bromate

Co BrO3



Final Formula

(Co+2)x(BrO3-1)y

= 0

2X = 1y

X(+2) + y(-1) = 0

X 1Y 2=


satisfies the equation

(BrO3)

2If there is only one atom

the “1” is not shownNext


nickel(III) acetate

Ni C2H3O2



Final Formula

(Ni+3)x(C2H3O2-1)y

= 0

3X = 1y

X(+3) + y(-1) = 0

X 1Y 3=



(C2H3O2)3


Next


lithium phosphate

Li PO4



Final Formula

(Li )x(PO4-3)y

= 0

1X = 3y

X(+1) + y(-3) = 0

X 3Y 1=

3

+1

Choose the lowest set of integers that


(PO4)1




Next

Practice Problems

By now you should have an idea of what is expected when naming covalent binary compounds using prefixes.

In order to master this naming system you need to practice until you feel proficient in naming compounds using prefixes.

Practice Problem #1Fe(NO3)3

Choose the correct name for the compound

1. Iron trinitrate

2. iron(I) nitrate

3. iron(III) nitrite

4. iron(III) nitrate

5. none of the abovenext

problemPolyatomic

IonsPeriodic Chart

Practice Problem #2sodium chlorite

Choose the correct formula for the compound

1. NaCl

2. NaClO

3. NaClO2

4. Na(ClO)2

5. none of the above

next problem

PrefixesPeriodic Chart

POLYATOMIC IONS


-1

bromate BrO3-1

bromite BrO2-1

hypobromite BrO-1

perchlorate ClO4-1

chlorate ClO3-1

chlorite ClO2-1

hypochlorite ClO-1

periodate IO4-1

iodate IO3-1

iodite IO2-1

hypoiodite IO-1

nitrate NO3-1

nitrite NO2-1

hydroxide OH-1

cyanide CN-1

thiocyanate SCN-1

acetate C2H3O2-1

Permanganate MnO4

-1

bicarbonate HCO3-1


-2

phthalate C8H4O4-2

sulfate SO4-2

sulfite SO3-2

chromate CrO4-2

dichromate Cr2O7-2

oxalate C2O4-2

peroxide O2-2


-3

phosphite PO3-3

arsenate AsO4-3


NH4+1

return

N

Oxidation Numbers (most common)

La Hf Ta Re OsCe Ba Tl Pb Bi Po At RnIr Pt Au Hg

Y Zr Nb Mo Tc RuRb Sr In Sn Sb Te I XeRh Pd Ag Cd

Sc Ti V Cr Mn FeK Ca Ga Ge As Se Br KrCo Ni Cu Zn

Al Si P S Cl ArNa Mg

B C O F NeLi Be

H H He

Ac Rf Db Sg Rh HsFr Ra Mt

+1+2+31A

2A

8A

0-4-3-2-17A

6A5A4A3A

W

Nd Pm Sm Eu Gd TbCe Pr Yb LuDy Ho Er Tm

Np Am Cm BkTh Pa No LrCf Es Fm MdU Pu

Click on element to see its oxidation number(s)

+1 +2 +2 +3 +2 +4

return

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