1. 4.1 Representing Ionic Compounds

2. 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.

4. The Periodic Table and Valence Electrons
Group 8 = 8 valence electrons
Except for He, it has 2 electrons
Group 1 = 1 valence electron
Group 2 = 2 valence electrons
Each column is called a “group”
13, 14, 15, 16, 17
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.

5. 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)

6. 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)

7. Naming Binary Ionic Compounds…
The metal ion is always written first and keeps its whole name
The non-metal is written second and has a slight change, the ending (suffix) is changed to –ide
-example: Na2S – sodium sulfide

8. Writing Formulas for Binary Ionic Compounds…
-example: magnesium chloride Step 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 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

9. Writing Formulas for Binary Ionic Compounds…
-example: lithium oxide Step 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 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- ion 2(1+) + (2-) = 0 Step 4: Write the formula using subscripts to indicate the number of ions of each type Li2O

10. The Cross-Over Method
-example: lithium oxide Step 1: Write the symbols with the metal first Li O Step 2: Cross-Over Rule – Write the ionic charge above each symbol and cross over the amount of charge The formula is Li2O

11. The Cross-Over Method
-example: calcium oxide Step 1: Write the symbols with the metal first Ca O Step 2: Cross-Over Rule – Write the ionic charge above each symbol and cross over the amount of charge Ca O The formula is Ca2O2 Step 3: Reduce the Chemical Formula - Dividing by common factor of 2, we get: CaO

12. The Zero-Sum Rule
The 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

13. Naming Binary Ionic Compounds having Multivalent Metals…
-example: FeS 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 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-

14. -example: FeS Step 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 The name of the metal ion is iron(II) Step 8: Write the name of the compound. iron(II) sulfide

15. Naming Ionic Compounds having Multivalent Metals…
Binary Ionic Compounds
Naming Ionic Compounds having Multivalent Metals…
-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 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-

16. -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

17. Writing Formulas for Binary Ionic Compounds having Multivalent Metals…
-example: tin(IV) sulfide Step 1: Write the symbols with the metal first Sn S Step 2: Cross-Over Rule – Write the ionic charge above each symbol and cross over the amount of charge Sn S The formula is Sn2S4 Step 3: Reduce the Chemical Formula - Dividing by common factor of 2, we get: SnS2

18. Ternary Ionic Compounds: Ionic Compounds with Polyatomic Ions
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

19. Ionic Compounds with Polyatomic Ions
Answers
Ca(OH)2
CuSO4
NH4NO3
Co2(CO3)3
- calcium hydroxide
- copper(II) sulfate
- ammonium nitrate
- cobalt(III) carbonate

20. Most Common Polyatomic Ions
One extra oxygen
"per-____-ate"
Common/Normal
Just 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

21. Ionic Compounds with Polyatomic ions
Writing Formulas …
-example: aluminum carbonate
Step 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.
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

22. Ionic Compounds with Polyatomic ions
Writing Formulas …
-example: ammonium sulfate
Step 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.
NH SO4
Step 3: Use subscripts to show the ratio of ions. Place the polyatomic ion in brackets, if it needs a subscript.
(NH4)2SO4