Use the octet rule as a guide to determine the
charge on ions formed by main group elements
Non-metals gain electrons to attain a
noble gas configuration
Metals can readily attain a full octet (noble gas configuration)
by losing electrons
-1
• metals form positive ions (cations)
+
17 p+
-1
17 p+
Non-metals can readily attain a full octet (noble gas configuration)
by gaining electrons
• non-metals form negative ions (anions)
Cl – ion
1s2 2s2 2p6 3s2 3p6
[Ar]
Cl atom
1s2 2s2 2p6 3s2 3p5
[Ne] 3s2 3p5
Determining ion charge: Non-metals
Non-metals gain electrons to attain a
noble gas configuration
Group 8A elements: Noble gases
• these elements have very stable electron configurations
and do not form ions
-2
-1
8A
1A
2A
8 p+
+
3A
5A
6A
7A
He
Ne
8 p+
-1
4A
3B
4B
5B
6B
7B
8B
1B
2B
Ar
Kr
Xe
O atom
1s2 2s2 2p4
[He] 2s2 2p4
O2– ion
1s2 2s2 2p6
[Ne]
Rn
Transition elements
Main Group elements
Determining ion charge: Non-metals
Determining ion charge: Non-metals
Group 7A elements: Halogens
• these elements only form one kind of negative ion (-1 charge)
• gain of one electron results in noble gas structure (octet)
Group 6A elements
• these elements only form one kind of negative ion (-2 charge)
• gain of two electrons results in noble gas structure (octet)
8A
1A
2A
3A
3B
4B
5B
6B
7B
8B
1B
4A
5A
6A
2B
7A
He
F-
Ne
Cl -
Ar
Br -
Kr
I-
Xe
8A
1A
2A
3A
3B
4B
5B
6B
7B
8B
1B
4A
5A
2B
7A
O 2-
F-
Ne
S2-
Cl -
Ar
Se2- Br -
Kr
I-
Rn
Transition elements
Main Group elements
Main Group elements
Determining ion charge: Non-metals
Determining ion charge: Non-metals
Group 5A elements
• the non-metals in this group only form one kind of negative ion (-3 charge)
• gain of three electrons results in noble gas structure (octet)
8A
1A
2A
3A
4B
5B
6B
7B
8B
1B
2B
4A
5A
6A
7A
He
N 3- O 2-
F-
Ne
P3-
Cl -
Ar
Se2- Br -
Kr
S2-
I-
Group 4A elements
• the non-metal in this group (carbon) does not form ions
8A
1A
2A
3A
3B
4B
5B
6B
7B
8B
Xe
Main Group elements
1B
2B
6A
7A
He
4A
5A
C
N 3- O 2-
F-
Ne
P3-
Cl -
Ar
Se2- Br -
Kr
S2-
I-
Rn
Transition elements
Xe
Rn
Transition elements
3B
He
6A
Xe
Rn
Transition elements
Main Group elements
Ionic bonds
Reaction between sodium and chlorine
An ionic bond is formed by the attraction between two
oppositely charged ions
• Ionic bonds are formed whenever electrons are
transferred from one ion to another
• Metals (which have relatively weak attraction for their
valence electrons) tend to form ionic bonds when they
combine with non-metals
• The attraction between ions is very strong, which results in
high melting points for ionic compounds (often > 300°C)
11 p+
17 p+
Na +
Cl –
Na+
Cl-
NaCl (ionic compound)
Strong attraction between positive Na+ and negative Clforms an ionic bond
Ionic substances are not truly molecular
Ions in an ionic compound are packed
closely together in an orderly, repeating
arrangement (crystal structure)
Example:
Sodium chloride bonds ionically
• it consists of a large aggregate of
positive and negative ions
• individual molecules of NaCl do not exist
• NaCl represents the formula unit for
sodium chloride (i.e., the smallest,
simplest neutral unit of the compound)
Properties of Ionic Compounds
• crystalline solids at room temperature
• high melting and boiling points
• hard and brittle (will shatter if struck sharply)
• often soluble in water or other polar solvents
• will conduct electricity when melted or dissolved in water
Formulas of ionic compounds
Formulas of ionic compounds
The formula of an ionic compound shows the number and types
of ions that make up the compound
The formula of an ionic compound shows the number and types
of ions that make up the compound
• element symbols indicate the type of ions in the compound
• subscripts indicate the number of each ion in the compound
• the overall charge from the positive and negative ions in the
• element symbols indicate the type of ions in the compound
• subscripts indicate the number of each ion in the compound
• the overall charge from the positive and negative ions in the
Example:
Example:
Magnesium chloride
sodium sulfide
compound must be equal to zero
MgCl2
compound must be equal to zero
Na2S
Mg loses 2e-
Each Cl
gains 1e-
One
Two
magnesium ion chloride ions
Mg2+
2 Cl–
Each Na
loses 1e-
S gains 2e-
Charge Balance: (2+) + [ 2 x (1–) ] = 0
Two
sodium ions
2 Na+
One
sulfide ion
S2–
Charge Balance: [ 2 x (1+) ] + (2–) = 0
Rules for writing formulas of ionic compounds
Rules for writing formulas of ionic compounds
1. Identify the types and numbers of ions that make up the
compound
1. Identify the types and numbers of ions that make up the
compound
•
the overall charge from the positive and negative ions in the
compound must be equal to zero
•
the overall charge from the positive and negative ions in the
compound must be equal to zero
2. List the cation first, then the anion
2. List the cation first, then the anion
3. Do not write the charges for the ions in the formula
3. Do not write the charges for the ions in the formula
4. Use parentheses around polyatomic ion groups if a subscript is
necessary
4. Use parentheses around polyatomic ion groups if a subscript is
necessary
Example: Magnesium chloride
CHARGE BALANCE
Example: Iron (III) hydroxide
CHARGE BALANCE
Cation: Magnesium ion (Mg2+)
One Mg2+ ion: 1 x (+2) = +2
Cation: Iron (III) ion (Fe3+)
One Fe3+ ion: 1 x (+3) = +3
Anion: Chloride ion (Cl–)
Two Cl– ions: 2 x (–1) = –2
Anion: Hydroxide ion (OH–)
Three OH– ions: 3 x (–1) = –3
Formula: MgCl2
2+
–
[ not Cl2Mg or Mg Cl2 ]
Formula: Fe(OH)3
3+
–
[ not FeOH3 or (OH)3Fe or Fe (OH )3 ]
Naming ionic compounds: Compounds containing
metals that form only one type of cation
Naming ionic compounds: Compounds containing
metals that form only one type of cation
Step 1
Identify the cation (metal)
and anion (nonmetal)
Step 1
Identify the cation (metal)
and anion (nonmetal)
Step 2
Name the cation from its
element name
Step 3
Name the anion from its
element name plus the
ending -ide
Step 4
Write the name of the
cation first and the name
of the anion second
Example:
Na+
Cl -
Step 2
Name the cation from its
element name
Formula: NaCl
Metal: sodium
Non-metal: chlorine
Cation name:
sodium
Anion name:
chloride
Compound
name:
sodium chloride
Naming ionic compounds: Compounds containing
metals that form more than one type of cation
Step 1
Identify the cation (metal)
and anion (nonmetal)
Example:
Cu+
Cl -
Step 2
Determine the charge of the cation
Step 3
Name the cation from its
element name, followed by a
Roman numeral in parentheses
indicating its charge
Step 4
Name the anion from its element
name plus the ending -ide
Step 5
Write the name of the cation first
and the name of the anion second
Step 3
Name the anion from its
element name plus the
ending -ide
Step 4
Write the name of the
cation first and the name
of the anion second
Example:
Br -
Ca2+
Br -
Formula: CaBr2
Metal: calcium
Non-metal: bromine
Cation name:
calcium
Anion name:
bromide
Compound
name:
calcium bromide
Naming ionic compounds: Compounds containing
metals that form more than one type of cation
Step 1
Identify the cation (metal)
and anion (nonmetal)
Example:
Cl -
Cu+
Cl -
Step 2
Determine the charge of the cation
Formula: CuCl
Metal: copper
Non-metal: chlorine
Cation charge:
+1 (Cu+1)
Cation name:
copper(I)
Anion name:
chloride
Compound
name:
copper(I) chloride
Step 3
Name the cation from its
element name, followed by a
Roman numeral in parentheses
indicating its charge
Step 4
Name the anion from its element
name plus the ending -ide
Step 5
Write the name of the cation first
and the name of the anion second
Formula: CuCl2
Metal: copper
Non-metal: chlorine
Cation charge:
Cation name:
Anion name:
Compound
name:
+2 (Cu+2)
copper(II)
chloride
copper(II) chloride
Polyatomic ions
Naming review
monoatomic ions -- ions composed of a single atom (e.g., Na+, S2-)
CaO
calcium oxide
polyatomic ions -- ions composed of more than one atom
CoCl3
cobalt(III) chloride
–
H
ZnCl2
+
zinc chloride
N
SnO2
O
O
H
H
tin(IV) oxide
–
N
O
H
–
O
peroxide ( O22- )
nitrate ( NO3– )
ammonium ( NH4 )
+
Polyatomic ions
Positively charged polyatomic ions
Most common polyatomic ions are negatively charged
Name
Name
Formula
-1
Cyanide
CN-
-
-1
Formula
Hydroxide
OH-
Nitrate
NO3
Nitrite
NO2-
Sulfate
Charge
Charge
-1
Chlorate
ClO3
-
-1
-1
Bromate
BrO3-
-1
SO42-
-2
Permanganate
MnO4-
-1
Sulfite
SO32-
-2
HS-
-1
Phosphate
PO43-
-3
Hydrogen
sulfide
Carbonate
CO32-
-2
Acetate
C2H3O2-
-1
Chromate
CrO4
-2
Hydrogen
carbonate
HCO3
Dichromate
Cr2O7
-
-1
commonly called “bicarbonate”
22-
-2
O
Thankfully, there are only a couple of positively charged
polyatomic ions that are commonly encountered, so these
are pretty easy to remember:
ammonium
NH4+
-- don’t confuse this with
ammonia (NH3, neutral)
hydronium
ion
H3O+
-- we’ll see this more when
we talk about acids and
aqueous solutions
Rules for naming ionic compounds
1. Based on the compound formula, identify the ions that make up
the compound
•
for elements that can form more than one type of positive ion,
include Roman numeral in parentheses indicating charge
-- most transition metals (exceptions: Zn, Ag, Cd)
-- Pb and Sn
2. Name the cation(s) first
3. Follow with the name of the anion
Compound
Cation(s)
CuSO4
Cu2+
[ copper (II) ]
Na2O
Na+ [sodium]
NH4NO3
NH4+ [ammonium]
Anion
SO4
2–
[sulfate]
Compound name
copper (II) sulfate
O2– [oxide]
sodium oxide
NO3– [nitrate]
ammonium nitrate
Homework Assignment
Chapter 4:
Problems 4.60, 4.64, 4.65, 4.66, 4.68, 4.70, 4.72,
4.74, 4.75, 4.97
Naming review
KMnO4
Al2(CrO4)3
potassium permanganate
aluminum chromate
CuCO3
copper(II) carbonate
NaKSO4
sodium potassium sulfate
MgNH4PO4
magnesium ammonium phosphate
Ba(NO2)2
barium nitrite
Cu2SO4
copper(I) sulfate