4.1 Representing Ionic Compounds

Forming Ionic Compounds• Ionic compounds are formed when one or more valence electrons

(electrons in the outer energy level) are transferred from a metal atom to a non-metal atom. – Example: sodium chloride (NaCl)

• they are made up of positive ions (cations) and negative ions (anions) that are attracted to each other.

• the two oppositely charged ions are attracted to each other by a force called an ionic bond.

The Periodic Table and Valence Electrons

•Each column is called a “group”

Except for He, it has 2 electrons

•Octet Rule: The loss and gain of electrons allows each atom to form a full outer energy level of electrons and, therefore, become stable (with the same number of electrons as the closest noble gas)•Scientists often refer to this arrangement as a stable octet.

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Ionic structure / properties• Ionic compounds are solids at SATP. In

their solid form they form ionic crystals. These are more commonly known as salts.

• high melting and boiling points

• many are brittle

• when ionic compounds are dissolved in water, they dissociate into their ions and the solutions conduct electricity. – NaCl(s) Na+

(aq) + Cl-(aq)

Types of Ionic Compounds…Binary Ionic Compounds: composed of only 2 different elements (a metal cation and a non-metal anion)

some binary ionic compounds contain a multivalent metal – these have more than one ion charge (listed in the periodic table)

Ternary Ionic Compound: composed of 3 different elements (one of the ions is polyatomic – made up of more than one element)

Naming Binary Ionic Compounds…

Binary Ionic Compounds

1.The metal ion is always written first and keeps its whole name

1.The non-metal is written second and has a slight change, the ending (suffix) is changed to –ide

-example: Na2S – sodium sulfide

Writing Formulas for Binary Ionic Compounds…

-example: magnesium chlorideStep 1: Write the symbols with the metal first

Mg Cl

Step 2: Write the ionic charge above each symbol to indicate the stable ion that each element forms

2+ 1-Mg Cl

Step 3: Determine how many ions of each type you need so that the total ionic charge is zero

One Mg2+ ion will balance the charge of two Cl- ions(2+) + 2(1-) = 0

Step 4: Write the formula using subscripts to indicate the number of ions of each type MgCl2

Binary Ionic Compounds

Writing Formulas for Binary Ionic Compounds…

-example: lithium oxideStep 1: Write the symbols with the metal first

Li O

Step 2: Write the ionic charge above each symbol to indicate the stable ion that each element forms

1+ 2-Li O

Step 3: Determine how many ions of each type you need so that the total ionic charge is zero

Two Li1+ ions will balance the charge of one O- ion2(1+) + (2-) = 0

Step 4: Write the formula using subscripts to indicate the number of ions of each type Li2O

The Cross-Over Method

-example: lithium oxideStep 1: Write the symbols with the metal first

Li O

Step 2: Cross-Over Rule – Write the ionic charge above each symbol andcross over the amount of charge.

1+ 2-Li O

The formula is Li2O

The Cross-Over Method

-example: calcium oxideStep 1: Write the symbols with the metal first

Ca O

Step 2: Cross-Over Rule – Write the ionic charge above each symbol andcross over the amount of charge

2+ 2-Ca O

The formula is Ca2O2

Step 3: Reduce the Chemical Formula - Dividing by common factor of 2, we get:

CaO

The Zero-Sum RuleThe sum of all the charges in the chemical formula of the compound MUST EQUAL ZERO.

Example: Al2S3

Ratio of 2 Al atoms : 3 S atoms

Al cation +3 charge S anion -2 charge

2(+3) + 3(-2) = ZERO! Al S

Naming Binary Ionic Compounds having Multivalent Metals…

Binary Ionic Compounds

-example: FeSStep 1: Identify the metal

Iron (Fe)

Step 2: Verify that the metal can form more than one kind of ion by checking the periodic table.

2+ 3+Fe and Fe

Step 3: Determine the ratio of the ions in the chemical formula 1 iron : 1 sulfide

Step 4: Note the charge of the anion 2-

-example: FeSStep 5: The positive and negative charges must balance out so that the net charge is 0.

Total negative charge: 2-Total positive charge: 2+

Step 6: Determine what charge the metal ion must have to balance the anion.

1(Fe ?) = 2+Therefore, the charge on the iron must be 2+.

Step 7: Write the name of the metal ion – include a roman numeral to show which charge the ion has in brackets, after the name. See Table 4.5 on pg. 147.

The name of the metal ion is iron(II)

Step 8: Write the name of the compound.iron(II) sulfide

Naming Ionic Compounds having Multivalent Metals…

Binary Ionic Compounds

-example: Fe2S3

Step 1: Identify the Metal

Iron (Fe)

Step 2: Verify that the metal can form more than one kind of ion by checking the periodic table

2+ 3+Fe and Fe

Step 3: Determine the ratio of the ions in the chemical formula 2 iron : 3 sulfide

Step 4: Note the charge of the anion 2-

-example: Fe2S3

Step 5: The positive and negative charges must balance out so that the net charge is 0.

Total negative charge: 6- (3 X 2-)Total positive charge: 6+

Step 6: Determine what charge the metal ion must have to balance the anion.2(Fe ?) = 6+

Therefore, the charge on the iron must be 3+.

Step 7: Write the name of the metal ion – include a roman numeral to show which charge the ion has in brackets after the name.

The name of the metal ion is iron(III)

Step 8: Write the name of the compound.iron(III) sulfide

Writing Formulas for Binary Ionic Compounds having Multivalent Metals…

Binary Ionic Compounds

-example: tin(IV) sulfideStep 1: Write the symbols with the metal first

Sn S

Step 2: Cross-Over Rule – Write the ionic charge above each symbol andcross over the amount of charge

4+ 2-Sn S

The formula is Sn2S4

Step 3: Reduce the Chemical Formula - Dividing by common factor of 2, we get:

SnS2

• naming compounds with polyatomic ions is similar to naming other ionic compounds

• You should note that compounds with polyatomic ions have names ending in -ate or –ite, not -ide

• Note that most are negative, except ammonium, NH4

+ (see table 4.7 on pg. 148)

• Name Ca(OH)2, CuSO4, NH4NO3, Co2(CO3)3

Ternary Ionic Compounds:Ionic Compounds with Polyatomic Ions

- calcium hydroxide

- copper(II) sulfate

- ammonium nitrate

- cobalt(III) carbonate

Ca(OH)2

CuSO4

NH4NO3

Co2(CO3)3

Answers

Ionic Compounds with Polyatomic Ions

Most Common Polyatomic IonsOne extra oxygen"per-____-ate"

Common/NormalJust memorize this one and you’ll know the rest

One less oxygen”-ite"

Two less oxygens"hypo-____-ite"

NO41-

pernitrate

NO31-

nitrate

NO21-

nitrite

NO1-

hyponitrite

CO42-

percarbonate

CO32-

carbonate

CO22-

carbonite

CO2-

hypocarbonite

ClO41-

perchlorate

ClO31-

chlorate

ClO21-

chlorite

ClO1-

hypochlorite

SO52-

persulfate

SO42-

sulfate

SO32-

sulfite

SO22-

hyposulfite

PO53-

perphosphate

PO43-

phosphate

PO33-

phosphite

PO23-

hypophosphite

Writing Formulas …

-example: aluminum carbonateStep 1: Using the periodic table and a table of common polyatomic ions,

identify each ion and its charge.

Aluminum: Al3+

Carbonate: CO32-

Step 2: Cross-Over Rule – Cross over the amount of charge.

3+ 2-Al CO3

Step 3: Use subscripts to show the ratio of ions. Place the polyatomic ion in brackets, if it needs a subscript.

Al2(CO3)3

Ionic Compounds with Polyatomic ions

Writing Formulas …

-example: ammonium sulfateStep 1: Using the periodic table and a table of common polyatomic ions,

identify each ion and its charge.

Ammonium: NH4 +

Sulfate: SO4 2-

Step 2: Cross-Over Rule – Cross over the amount of charge.

1+ 2-NH4

SO4

Step 3: Use subscripts to show the ratio of ions. Place the polyatomic ion in brackets, if it needs a subscript.

(NH4)2SO4

Ionic Compounds with Polyatomic ions